Pressure Compensated Control Valve

Abstract

Each spool of a control valve has its own pressure compensated flow controlling mechanism, and a single unloading valve serves to divert the pump output to tank when all of the valve spools are in neutral positions. In a control valve of sectional construction, pressure signals necessary for operation of the flow controlling mechanism and/or the unloading valve are obtained through pilot passageways having portions formed as grooves in the surfaces of the sections at their junctions. The flow controlling mechanisms can be provided with pressure responsive valve plungers which adapt their respective spool sections for parallel operation, or for series-parallel operation, or even a mixture of both; and with a minimum of modification, series operation is also made possible.

Description

BACKGROUND OF THE INVENTION

This invention relates to pressure compensated control valves which, as is well known, not only govern the operativeness of a fluid motor and the direction of its operation, but which also maintain the motor in operation at a constant selected speed despite variations in the load thereon or in the pressure of supply fluid available for motor operation.

In general, a conventional pressure compensated control valve comprises a valve spool which is movable from a neutral position to at least one operating position to direct pressure fluid from a supply passage to a motor port of the valve via a feeder passage having portions upstream and downstream of the bore containing the valve spool, and a pressure actuatable flow controlling plunger to regulate fluid flow from the supply passage to the upstream feeder passage portion in accordance with variations in the pressure differential between said feeder passage portions.

In the above described arrangement, the valve spool is provided with throttle notches to define an orifice in the feeder passage, through which fluid flow to the motor can be metered. The size and flow limiting effect of the orifice, of course, if determined by the extent the valve spool is displaced from neutral. The pressure compensated flow controlling plunger is automatically actuatable to regulate flow of supply fluid to the upstream side of the orifice in accordance with variations in the pressure drop thereacross. The result is that a substantially uniform pressure drop is maintained across the orifice set by the valve spool, to assure a substantially uniform speed of motor operation, at least until the valve spool is adjusted to make the orifice larger or smaller.

When the pressure compensated plunger is in a flow regulating position maintaining flow of a metered amount of pressure fluid to a selected motor port of the control valve at a constant rate, excess supply fluid is ordinarily diverted by the plunger to a bypass for return to tank. This bypass is wide open when the valve spool is in its neutral position, so that all pump fluid then entering the control valve can flow to tank via the pressure compensated flow control mechanism and unload the pump.

For this reason, the pressure compensated plunger of a conventional control valve was held in its bypass open position under force exerted thereon by pump fluid entering the control valve, and the pressure compensating valve mechanism also served as a pump unloading valve.

Since the plungers of pressure compensating mechanisms were normally urged toward bypass closing positions under substantial spring force, the pump normally had to overcome such spring force before its output could be returned to tank in the neutral condition of the control valve.

This posed a particularly serious problem in multi-spool control valves having a pressure compensated flow control plunger for each valve spool, with pump output fluid flowing serially past all of the plungers to unload the pump when all of the valve spools were in their neutral positions. To avoid having the pump pressure largely dissipated in overcoming the load represented by the combined forces of the several plunger springs in neutral, it was customary to provide only very weak springs on the plungers. As a result, the pressure compensated plungers then failed to dependably maintain fluid flow to an associated motor port at the precisely metered rate desired. It has been proposed to use a separate bypass valve in combination with a pressure compensated control valve, to relieve the pressure compensating valve mechanism of its pump unloading function. The U.S. Pat. to McMillen No. 3,592,216, issued July 13, 1971, discloses such an expedient, but in an arrangement that is far from satisfactory.

The bypass valve used in U.S. Pat. No. 3,592,216 has a valve member which must be urged toward a bypass closing position by a strong spring. The force of that spring, of course, must be overcome by the pump when all of the control valve spools are in their neutral positions. The patent mentions that the unloading valve member could be biased toward closed position by a 50 psi spring, which force is augmented by the pressure of the load on the cylinder to which pressure fluid is directed by any of the control spools of the valve mechanism. However, the unloading valve will open any time line losses exceed the 50 psi spring force tending to hold the valve member closed. This is to say that there could easily be a 60 psi line loss between the pump and whichever motor port of the actuated control valve is receiving pressure fluid from the pump, and the pump would have to supply fluid at 60 psi above the pressure needed at the service port for operation of the cylinder. Thus, for example, if the pressure at the motor port were 1,500 psi, the fluid pressure exerting closing force upon the unloading valve member could not exceed 1,500 psi, but the pump output pressure would have to exceed 1,560 psi if the line losses between the pump and the motor port were 60 psi.

It is clear, therefore, that the spring biasing the unloading valve toward its bypass closing position could not be the 50 psi spring mentioned in the McMillen patent, but it would have to be substantially stronger in order to keep the unloading valve closed if the line losses were as great as 60 psi. In this respect, the force of any check valve spring, or the spring acting on the plunger of a pressure compensating valve in the supply line leading to the motor port must also be considered as line loss and adds thereto.

SUMMARY OF THE INVENTION

It is one of the objects of this invention to provide a pressure compensated hydraulic control valve mechanism wherein the above referred to problems are solved in a most practicable way.

More specifically, it is a purpose of this invention to provide a pressure compensated control valve mechanism wherein the pump can be relieved of pressure through an unloading valve, as distinguished from a bypass valve, and in a way that enables an exceptionally light spring to be used on the unloading valve member while enabling each compensating plunger to be biased by the strong spring force necessary for dependable and precise metering of fluid flow to the work port or ports governed by the associated valve spools.

Another object of the invention resides in the provision of a pressure compensated control valve with an unloading valve mechanism such as mentioned above, and wherein actuation of any control spool to an operating position closes a venting passage for the chamber in which the unloading valve member operates and results in the application of bypass closing force thereto.

In this respect, it is a further object of the invention to provide a hydraulic control valve mechanism such as described in the two preceding paragraphs, wherein pressure signals such as are required for operation of the unloading valve and pressure compensating valve are derived from the fluid supply passage at a location upstream from the valve spool to which the supply passage leads, and wherein said signals are transmitted to the unloading and pressure compensating valve mechanisms via pilot passages that can have portions formed in one surface of the control section when the valve mechanism is of sectional construction.

Another object of the invention resides in the provision of a control valve mechanism with pressure compensated plungers which provide for parallel or for series-parallel operation, or a combination of both types; and wherein true series operation is also possible.

Still another object of the invention is to provide a pressure compensated control valve mechanism of sectional construction, having an inlet section in which is incorporated an unloading valve as well as other pressure sensitive valve means to provide for void relief under certain operating conditions of the valve mechanism.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate complete examples of several embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is an elevational view of an open center type sectional control valve mechanism of this invention, comprised of a stack of three control sections;

FIG. 2 is a more or less diagrammatic view of the control valve seen in FIG. 1, showing the various sections separated from one another;

FIG. 3 is a fragmentary sectional view illustrating how venting of the unloading valve chamber is controlled by the various valve spools of the stack;

FIG. 4 is a fragmentary detail view looking at the underside of one of the control sections;

FIG. 5 is an enlargement of part of the inlet section seen in FIG. 2;

FIG. 6 is a sectional view taken on the line 6--6 in FIG. 2, and at an enlarged scale;

FIG. 7 is a view similar to FIG. 2 but showing a closed center type control valve of this invention;

FIG. 8 is a bottom detail view of one of the control sections seen in FIG. 7;

FIG. 9 is a fragmentary detail view, in section, showing how pilot fluid for the unloading valve chamber is obtained from the feeder passages in the valve sections;

FIG. 10 is a sectional view taken on the line 10--10 in FIG. 7; and

FIG. 11 discloses a control section adapted for series operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the accompanying drawings, the control valve of this invention has been shown by way of example as comprising a sectional valve having three control sections 10, 11 and 12 connected together in a stack, and end sections 13 and 14 at the top and bottom, respectively, of the stack. At their junctions 15, the sections are provided with flat finished surfaces S which have intimate mating engagement with one another.

The top section 13 constitutes an inlet section having an inlet passage or port 16 to receive pressure fluid from a pump (not shown), and in the present case the inlet section is also provided with an outlet passage or tank port 17. Persons skilled in the art will realize, however, that the tank port could just as well be located in the bottom section 14. The inlet section 13 also has a low pressure passage 18 which extends thereacross to have its opposite ends open to the undersurface S thereof at widely spaced zones.

The inlet passage 16 also opens to the undersurface S of the inlet section 13, and constitutes the upper end portion of a supply passage L1 which extends down through all the control sections of the stack, and which joins with a low pressure passage 19 in the bottom section 14. As is customary, the supply passage is comprised of upstream and downstream carryover branches 20 and 21 in each of the control sections.

The upstream branch 20 of the supply passage in each control section opens to the upper face thereof to be in communication with the downstream branch 21 in the control section thereabove. However, the branch 20 in the uppermost control section registers with the inlet passage 16, while the branch 21 in the lowermost control section opens to the low pressure passage 19 in the bottom section 14, through a suitable hole 22 therein.

Since the control sections and their respective compensating valve mechanisms are identical, the following description of section 10 applies to each of them. The section comprises a body with two parallel spaced apart bores 23 and 24 therein. The bore 24 is longer and is spaced to one side of the supply passage, but the shorter bore 23 is intersected by it.

A valve element 25 in the form of a spool is reciprocably received in the longer bore 24, while each shorter bore 23 accommodates the plunger P of a pressure compensating valve mechanism 26. Note that the upstream and downstream branches 20 and 21 of the supply passage open to the shorter bore 23 at axially spaced zones, to be normally freely communicated with one another through said bore.

The supply passage branch 20 can be considered as an inlet for the pressure compensating valve mechanism 26, and it has a service outlet 20' at the side of the branch 20 remote from the branch 21, and also communicable with the branch 20 under the control of the plunger P.

The valve spool 25 is movable in its bore from the neutral position thereof shown, to operating positions at opposite sides of neutral, to direct pressure fluid to a selected one of a pair of motor ports 27, 28, via a feeder passage 29, and to direct motor exhaust fluid from the non-selected motor port to a low pressure passage 30 adjacent thereto. The low pressure passages intersect the bore 24 at locations outwardly of the junctions of the latter with the motor ports.

These low pressure passages register with similar passages in the adjoining control sections to provide low pressure lines L2, which communicate with the low pressure passage 18 in the top section at their upper ends, and with the low pressure passage 19 in the bottom section at their lower ends.

The feeder passage 29 comprises a portion 31 which is upstream from the longer bore and which bridges the bores 23, 24. This upstream feeder passage portion 31 is connected with the outlet 20' of the pressure compensating valve mechanism 26, and it can be considered as providing a part or branch of the supply passage. The feeder passage also comprises a bridge-like portion 32 of inverted U-shape, downstream of the bore 24, and having ends which communicate therewith at zones adjacent to but axially inwardly of the zones of communication between said longer bore and the motor ports 27, 28. Hence, each motor port can be supplied from the downstream feeder passage portion 32, through the adjacent end thereof.

The entrance 33 to the downstream feeder passage portion 32 communicates with the bight of the latter intermediate its ends, and with the bore 24 at a zone spaced a short distance axially from the intersection of the bore with the upstream feeder portion 31. It will be noted that the entrance 33 to the downstream feeder passage portion 32 comprises a portion of the bore 24 which connects with the bight portion of said feeder passage through a load holding check valve 34, thus allowing a single check valve to serve both motor ports 27, 28.

With the arrangement described, the upstream feeder passage portion is communicable with its downstream portion through a zone 33 of the associated bore 24 under, or ahead of the load holding check valve 34 in the direction of fluid flow to the motor ports 27, 28.

A land 35 on the spool 25 controls communication between the upstream and downstream feeder passage portions through the bore 24, and orifice defining throttle notches 36 in the opposite ends of said land provide for adjustment of the amount of fluid allowed to flow to either motor port in accordance with the extent the valve spool 25 is displaced from its neutral position.

The purpose of the pressure compensating valve mechanism is to accurately govern the rate at which pressure fluid flows from the supply passage to the motor ports, and to regulate such flow in accordance with any variation in pressure differential between the upstream and downstream feeder passage portions. This is to say that the pressure compensating valve mechanism effects regulation of fluid flow from its supply passage branch 20 to the upstream feeder passage portion 31 in accordance with change in the pressure drop across the orifice provided by the throttle notches 36 through which pressure fluid flows to the downstream feeder passage portion 32.

For this purpose, the pressure differential across the orifice (between feeder passage portions 31 and 33), is imposed upon the opposite ends of the pressure responsive plunger P in its bore 23, so that movement of the plunger will either increase or decrease fluid flow from its outlet to the upstream feeder passage portion 31. The plunger is acted upon by an expansive spring 39, which tends to hold the plunger in its left hand limit of motion at which a circumferential groove 40 therein affords substantially free flow of supply fluid to the upstream feeder passage portion 31. In this limit of plunger motion, the land on its right hand end closes off communication between the upstream and downstream supply passage branches 20 and 21.

The opposite end portions of the bore 23 provide plunger actuating chambers 41 and 42 which are closed by plugs 43 and 44, respectively. The lands on the opposite ends of the plunger, at each side of its groove 40, project into the chambers 41 and 42 to be acted upon by the pressure of fluid therein. The left hand chamber 41 is communicated with the upstream feeder passage portion 31 through an axial passage in the plunger and a radial port 45 in the adjacent plunger land, whereby the pressure in chamber 41 will correspond to that at the upstream side of the orifice provided by the throttle notches 36 in the valve spool 25. The plunger P will be acted upon by such pressure and urged thereby toward the right, counter to the spring force thereon.

The chamber 42 at the other end of the plunger is communicated with the entrance 33 to the downstream feeder passage portion 32, at the outlet side of the orifice defined by the throttle notches 36 in the valve spool. A pilot or control passageway is provided for this purpose. This pilot passageway comprises a first hole 46 which opens at one end to chamber 42 and at its other end to a groove 47 in the undersurface S of the control section, and a second hole 48 which also opens at one end to said groove and at its other end to that zone 33 of the bore 24 which forms the inlet to the downstream feeder passage portion 32. It should be observed, however, that in each of control sections 10 and 12, the chamber 42 is vented through the bore 24 to a tank connecting passage 65' to be described at greater length hereinafter, when the valve spool 25 therein is in its neutral position. In control section 11, a small passageway 49 in the spool provides for venting the associated chamber 42 to one of the low pressure passages 39 via the downstream feeder passage portion 32 in the neutral position of the valve spool in section 11.

During operation, the pressure of fluid in chamber 42 will vary with the load on the fluid motor with which the selected motor port 27 or 28 is connected, and the force which such fluid exerts on the plunger P tending to move it toward the left will vary accordingly. As a result, whenever the valve spool 25 in section 10 is in an operating position directing a metered amount of pressure fluid to one end or the other of a fluid motor connected with ports 27, 28, the pressure compensated plunger P will seek a flow controlling position at which the force exerted on its left hand end by pressure fluid in upstream feeder passage portion 31 balances the opposing force on the plunger of spring 39 plus that of signal pressure in chamber 42 derived from zone 33 of the bore at the entrance to the downstream feeder passage portion 32. At that time, excess supply fluid can flow through plunger groove 40 to branch 21 of the supply passage and on to the inlet branch 20 of control section 11, where it is available for operation of a motor governed by the valve spool in that downstream section. If the load on the governed fluid motor increases, or if the pressure of supply fluid should decrease, the plunger P responds to the resulting increase in pressure differential between the upstream and downstream feeder passage portions by moving to the left to thereby compel a greater amount of supply fluid to flow through the feeder passage to the motor and prevent operation thereof at a speed lower than that set by the size of the metering orifice afforded by the throttle notches 36.

However, if the load on the governed motor decreases, or if pressure of supply fluid should increase, the plunger P will respond to the resulting decrease in pressure differential across the orifice by moving to the right, to let more supply fluid flow to the downstream supply branch 21, and thereby accordingly decrease flow of supply fluid to the upstream feeder passage portion 31.

With the above described arrangement, the flow of supply fluid to the upstream feeder passage portion 31 is normally regulated at the right hand end portion of the groove 40, by the adjacent land on the plunger in controlling flow of supply fluid to the downstream supply branch 21. However, if a spool of a downstream control section is operating a fluid motor at a higher pressure than the spool of an upstream control section, the flow of supply fluid to the upstream feeder passage portion 31 of the control section would then be regulated by the left hand land on the plunger, through the adjacent end of the plunger groove 40, at least until all pressure fluid delivered by the pump was demanded by the motor governed by the upstream control section.

The pressure compensated plungers P seen in FIG. 2 have been shown as all of the priority type, although parallel type plungers can also be used to advantage in a manner to be discussed later.

One of the outstanding features of the control valve mechanism described thus far is that the pilot passageway for subjecting chamber 42 of the compensating valve to fluid pressure leads to that portion 33 of the downstream feeder passage portion 32 which is at the entrance thereof and ahead of the check valve 34. Two highly significant advantages are thus realized. First, swarf or other foreign matter from the cylinder or other motor governed by the control valve is never allowed to come into contact with any part of the compensating valve mechanism where it might otherwise foul or clog orifices or otherwise interfere with its operation; and second, zone 33 at the entrance to the downstream feeder passage portion is common to both motor ports, to thus obviate the need for shuttle valves or the like.

Another important feature of the mechanism described thus far is that its inlet section 13 has an unloading valve mechanism 50 incorporated therein, to govern a bypass 51 between the inlet and outlet passages 16 and 17. Thus, when all of the valve spools 25 are in neutral, the unloading valve mechanism functions to divert all pump fluid from inlet port 16 to the tank port 17.

In some earlier pressure compensated control valve mechanisms, this pump unloading function was performed solely by the flow controlling valve mechanisms. For that purpose, their plungers were made responsive to pressure of pump fluid in the supply passage. Accordingly, the pump had to overcome the spring force acting on the plunger in order to move it to a position allowing all of the supply fluid to be diverted to tank in the neutral position of the control spool.

Unloading of the pump according to such past practice was particularly objectionable in control valve mechanisms having a number of valve spools and a pressure compensating valve mechanism for each of them. In that case, when the valve spools were all in neutral, the pump was forced to supply enough pressure to unseat the pressure compensated plungers of all the flow control valve mechanisms before its output could be returned to tank. Much of the pressure produced by the pump was thus dissipated in a multi-spool valve with the result that there could easily be insufficient pressure available to operate fluid motors governed by those valve spools most distant from the inlet.

Heretofore, the only solution to this problem was to provide the pressure compensated plungers of multi-spool control valves of the type herein concerned with substantially weak springs, to assure against the serious pressure drop that would otherwise result. While this expedient helped to solve the problem of pressure drop, it was nevertheless found to be objectionable in that the pressure compensated plungers were then no longer able to perform their flow controlling functions with the preciseness and dependability required in many fluid pressure operated systems.

According to this invention, the springs 39 acting upon the pressure compensated flow controlling plungers P can be as strong as necessary to assure precise control over fluid flow to the governed motor. This feature is made possible by the provision of the unloading valve 50, which in this case, as a substantially weak spring 53 to lightly urge its poppet type valve member 52 toward a position closing the bypass 51.

The poppet 52 is slidable axially in a bore 54 in the inlet section opening inwardly toward the inlet port 16. It is substantially tubular with a slightly reduced inner end portion which is adapted to engage an outwardly facing seat 55 on the inlet section, under the action of its spring 53, to close off communication between the inlet and outlet ports through the bypass 51. It should here again be observed that the spring 53 need only be strong enough to overcome frictional drag on the poppet resulting from its sliding fit in the bore 54.

The outer end of the bore is closed by a plug 56 which can also accommodate a pilot poppet 57 for a high pressure relief poppet 59 mounted inside the unloading poppet. The space between the plug and the rear of the poppet 52, however, defines a chamber 58 which is common to the unloading poppet and also to the inner high pressure relief poppet 59.

The relief poppet is also of tubular construction, and it is slidably mounted in the hollow interior of the unloading poppet 52 for movement toward and from a normally closed position at which its inner end engages an annular seat 60 in the inner end portion of the unloading poppet. A spring 61 yieldingly urges the inner poppet toward said closed position, to prevent inlet fluid from flowing to the bypass 51 through the hollow interior of the outer poppet and holes 62 in its side wall.

Pressure fluid from the inlet port is free to enter the hollow interior of the inner poppet 59 through the open front of the outer poppet and an orifice 63 in the inner end of the inner poppet. A stem 64 extends coaxially through the open front of the inner poppet and the space around its exterior defines the orifice 63. The stem 64 has an axial thrust transmitting connection with the pilot poppet 57.

From the above description of the unloading and relief valve mechanisms, it will be apparent that pressure fluid from the inlet port can fill the chamber 58 and exert force on the rear of the poppet assembly to hold both poppets closed. This holds true for the unloading poppet 52 only as long as a venting passage 65 for chamber 58 is closed; for when that venting passage is open, fluid can exit from chamber 58 faster than it flows thereinto from the inlet port, and inlet fluid there acts on the inner end of the unloading poppet to open it.

The venting passage 65 is controlled by the valve spools 25 in the control sections 10, 11 and 12. It is open when all of the spools are in their neutral positions so as to then permit the unloading poppet 52 to remain open under force which inlet fluid exerts upon its inner end, and thereby effect unloading of the pump. Movement of any one of the valve spools 25 out of its neutral position closes the venting passage, and thereby causes the unloading poppet to close as a result of the buildup in pressure which then takes place in it chamber 58.

FIG. 3 reveals how the venting passage 65 extends serially through the control sections and the spool bores therein, and how axially spaced lands 66 and 67 on the valve spools 25 control opening and closing thereof. As therein seen, the bore 24 in each control section is formed with axially adjacent enlargements 68 and 69 so spaced apart as to be communicated with one another by the circumferential groove between lands 66 and 67 when the associated valve spool is in its neutral position shown. Each control section also has coaxial holes 70 drilled part way thereinto, toward one another, from each of its surfaces S so that the holes in each control section will register with corresponding holes in adjoining sections. In each control section, the enlargement 69 is extended outwardly of its bore 24 toward one surface S to intersect the adjacent hole 70. Its companion enlargement 68 is similarly extended outwardly of the bore but toward the opposite surface S, to intersect the other hole 70 therein. In effect, this forms a zigzag venting passageway through all the control sections, capable of being closed off by the lands 66 and 67 on any spool 25 upon shifting thereof out of its neutral position.

The passageway 65 can lead to a tank passageway in the outlet section 14, but where the tank port is located in the inlet section 13, the venting passageway leads to an exhaust passage 72 in the inlet section. The exhaust passage 72 is at all times in open communication with the outlet port 17.

A portion 73 of the venting passageway 65 leads from the unloading valve chamber 58 to a small diameter bore 74 in one side of the inlet section, which bore is closed at its outer end by a plug 75. The bore 74 extends inwardly of the inlet section, parallel to the bore 54 containing the unloading poppet, and it intersects a hole 70' therein which opens to the undersurface of the inlet section, in register with the hole 70 in the control section therebeneath.

The hole 70 in the underside of the bottom control section 12 opens to a shallow indentation 77 in the upper surface S of the bottom section 14. This indentation communicates with a return portion 65' of the venting passage, leading back up through all the control sections of the inlet section 13. A suitable passage portion (not shown) in the inlet section communicates the upper end of the return portion 65' of the venting passage 65 with the exhaust passage 72 therein.

The pilot poppet 57 for the high pressure relief poppet controls a second venting passage 80 for the chamber 58 behind poppets 52 and 59. The venting passage 80 opens axially inwardly to the chamber 58 through a hole 81 in the inner end of plug 56, and it opens directly to the exhaust passage 72 through a radial hole 82 in the plug. The seat 83 for the pilot poppet 57, of course, is located intermediate the holes 81 and 82.

A spring 84 holds the pilot poppet closed against unseating force exerted on its inner end by pressure fluid in chamber 58. The pilot poppet opens, of course, whenever the pressure in any motor governed by the valve mechanism, and likewise present in chamber 58, rises to a predetermined high relief value. As soon as chamber 58 is vented through passage 80 the main relief valve will open under force of inlet pressure fluid on its inner end to relieve the system of excess pressure.

It should be observed that fluid expelled from any motor or motors governed by the various valve spools 25 is returned to the low pressure passage 18 in the inlet section. This low pressure passage is communicable with the exhaust passage 72 through a port 86 controlled by a low pressure relief valve 87. A spring 88 urges the relief valve toward the low pressure passage to a position closing the port 86, from which position it can be opened by force which return fluid in passage 18 exerts thereon through port 86. Whenever the pressure of fluid in passage 18 attains a predetermined low value which, for purposes of illustration, may be assumed to be in the neighborhood of 200 psi, the low pressure relief valve will be opened. Such opening of the low pressure relief valve, however, is governed by a pilot poppet 90 therefor.

By this arrangement, the low pressure relief valve will act more or less as an exhaust restriction to maintain sufficient pressure in the return lines L2 for efficient and prompt actuation of void control valves 91 which control flow of void relief fluid from the low pressure lines L2 back to either motor port 27 or 28. Each valve 91 will be caused to open whenever the pressure in its associated motor port drops to a value below the 200 psi pressure maintained in the low pressure passage 18 and in lines L2 connecting therewith.

Also for void relief purposes, the inlet secton 13 can be provided with a pressure reducing valve 92 which is mounted alongside the low pressure relief valve and controls flow of fluid through a bypass 94 between the inlet port 16 and the low pressure passage 18. This bypass leads through ports 95 and 96 at axially spaced locations in the wall of a cylinder 97 containing a spool type plunger 98. The plunger is urged by a spring 99 to one limit of motion in the cylinder at which a circumferential groove 100 in the plunger establishes communication between ports 95 and 96. Since ports 95 open to the inlet port 16 and ports 96 open to the low pressure passage 18, the latter is thus communicated with the inlet port.

When normal pressure conditions obtain in any hydraulic system governed by the valve spools 25, the pressure of fluid in the low pressure passage 18 (for example, 200 psi) exerts force on the plunger 98 to lift it against the action of its spring 99 to a position at which a land on the plunger closes off communication between ports 95 and 96 through the interior of the cylinder. It is only when pressure in the low pressure passage drops to some value between the setting of the low pressure relief valve and tank pressure (for example, 100 psi) that the diminished fluid pressure force tending to hold the plunger in bypass closing position is overcome by the force of is spring 99. The plunger then moves to bypass open position at which supply fluid can flow from the inlet port to the low pressure passage 18 for void relief purposes.

If desired, the valve spool in control section 11 may have, in addition to the two operating positions thereof already described, a high pressure regenerating position at which it effects concurrent communication of both of its motor ports 27, 28 with the supply passage via the feeder passage 29. This high pressure regenerating position is reached by shifting the valve spool a distance beyond one of its operating positions, to a position at which circumferential grooves 101 and 102 in the spool simultaneously communicate the motor ports 27, 28 with the opposite ends of the downstream bridge section 32 of feeder passage 29.

In some cases it may be desirable to provide one of the control sections with a valve spool having a free fall, or so-called regenerative float position in addition to its other two operating positions. The control section 12 is provided with such a valve spool. For that purpose, its spool has circumferential grooves which are capable of concurrently communicating motor ports 27 and 28 with one another through the bridge-like feeder portion 32 and of communicating one of said motor ports (27) with its adjacent low pressure passage 30. This regenerative float position is reached by shifting the valve spool to the left of neutral, beyond its position at which it communicates motor port 28 with the supply passage and motor port 27 with its low pressure passage 30.

A simple readily adjustable stop mechanism 104 is also provided for the valve spool in control section 10, to limit the extent of spool motion in the direction to pressurize motor port 28, and thus regulate maximum pump flow to the governed fluid motor via said port. This stop mechanism is carried by the cup-like housing 105 which encloses the centering spring mechanism for the valve spool 25 at one end thereof, and it comprises a screw 106 which is received in a threaded hole 107 in the housing 105 to be coaxial with the valve spool and normally spaced from the adjacent end thereof. A jam nut 108 threaded onto the outer end of the screw 106 and bearing against the housing holds the axial adjustment of the screw. Preferably, the screw is concealed by an acorn nut 109 threaded thereon, outwardly of the jam nut.

While the valve mechanism described above can be said to be of the open center type, FIG. 7 diagrammatically illustrates a closed center version of the control valve mechanism of this invention. It similarly comprises three superimposed control sections 110, 111 and 112 confined between top and bottom sections 113 and 114, respectively, and likewise features individual pressure compensating valve mechanisms 115 for each control section. A common unloading valve mechanism 116 in the inlet section at the top of the stack likewise takes over the pump unloading function usually performed by conventional compensating valve mechanisms. In this case, the supply passage L1 is dead-ended at the bottom section 114, but each pressure compensating valve mechanism 115 regulates fluid flow from its supply passage branch 20 to the associated feeder passage 29, as before, with one exception to be discussed hereinafter.

The valve spools 125 again control venting of the unloading valve chamber 58 through a venting passage 65, 65' like that previously described. However, as will appear shortly, pressurization of the unloading valve chamber 58 is here accomplished differently. The unloading valve mechanism comprises a hollow outer unloading poppet 52 and an inner high pressure relief poppet 127 the inner end of which is imperforate. Hence, pressure fluid in the inlet port 16 can exert opening force on the inner and outer poppets, but it cannot flow through them to the chamber 58 in which they operate to effect pressurization thereof in the manner described earlier, when any valve spool is moved to an operating position closing the chamber venting passage.

In this case, the unloading valve chamber 58 is pressurized by fluid from the outlet of any pressure compensating valve 115, or more particularly, by pressure of fluid present in the upstream feeder passage portion 31 controlled thereby after its associated valve spool has been shifted from neutral toward one of its operating positions the slight distance necessary to close the venting passage 65. As soon as the passage 65 is blocked by one of the valve spools 125, pump fluid entering the inlet port 16 can flow through the supply passage to the unloading valve chamber 58 via pilot control lines indicated by the numeral 128, which connect with each of the upstream feeder passage portions 31 and with the vent line 65 for chamber 58 at a location ahead of the upstream control section 110. Each of these control lines contains a check valve 129 which opens in the direction of fluid flow from its upstream feeder passage portion to chamber 58.

The pilot line 128 for each control section comprises a hole 130 which extends radially outwardly from the compensating bore 41 at its junction with the associated upstream feeder passage portion 31, to one surface S of the section. The hole 130 opens to said surface through a counterbore 131 containing a ball check 132 which is engageable with the seat at the bottom of the counterbore to close the hole 130. The ball 132 is held against displacement from its counterbore by the surface S of the adjoining control section.

The pilot line 128 also comprises registering holes 134 in the control sections 110, 111, and 112, opening at their ends to the opposite surfaces S of said sections, and communicating grooves 135 in those surfaces of the sections to which the counterbores 131 open, to link said counterbores with the hole 134. The uppermost one of the holes 134, of course, connects with the passage 65 in the inlet section so as to be in communication with the unloading valve chamber 58 therein.

The pressure compensating mechanisms 115 operate like those described earlier, although only that in the center control section 111 has a priority type plunger P like those described earlier. The pressure compensated plunger P1 in each of control sections 110 and 112 is of the parallel type having lands so spaced that flow of pressure fluid between is supply passage branches 20, 21 is never blocked, in any position of the compensating plunger. In this respect, it will be seen that another feature of the control valve mechanism of this invention is that priority and parallel type pressure compensated plungers can be used in any desired combination.

Springs 39 tend to hold the pressure compensated plungers in their left hand limits of motion, and they are preferably substantially strong, as for example, powerful enough to be overcome by fluid in the upstream supply passage branches 20 and associated upstream feeder passage portions 31 at pressures on the order of 200 psi, or even higher. The spring tending to hold the unloading poppet 52 open, however, is again substantially weak, and may exert a closing force thereon sufficient only to easily overcome frictional drag exerted thereon by the walls of its chamber. Hence, the closing force which the spring exerts on the poppet may be on the order of 50 psi, or considerably less.

When any valve spool 125 is shifted only slightly out of its neutral position toward one or the other of its operating positions, the vent line 65 for the unloading valve chamber is immediately blocked to compel pump fluid to flow through pilot control lines 128 to chamber 58 from the upstream feeder passage portions 31 then in full communication with their respective supply passage branches 20. This, of course, effects closure of the unloading poppet 52 and rise in the pressure of pump fluid in the inlet port 16 and the supply passage connecting therewith to the 200 psi value necessary to shift the compensating plungers to the right, to positions closing off the upstream feeder passage portions 31 from their associated supply passage branches 20. The pressure in the unloading valve chamber 58 will then also be at a value corresponding to that of the spring force acting on the compensating plungers (200 psi). Hence, with the supply passage blocked, the pressure of pump fluid in inlet passage 16 will quickly rise to a value sufficient to overcome the fluid pressure closing force then being exerted on the unloading poppet, and sufficient fluid will be bypassed to tank to maintain the 200 psi pressure at the inlet. It is highly important to observe, however, that the unloading poppet opens only in response to pressure in excess of that required to shift the pressure compensated plungers against the 200 psi force exerted thereon by their springs 39 at times when its chamber venting passage is blocked.

If desired, a small hole can be drilled in the sleeve of the high pressure relief poppet 127 in the interior of the unloading poppet 52, as shown, to allow leakage of pressure fluid from chamber 58 to the bypass ports 62 in the unloading poppet in an amount sufficient to vent out excess pressure and thereby assure opening of the bypass poppet in the manner described. This allows the unloading poppet to modulate at the average signal pressure and to be substantially unaffected by sudden pressure increases such as are commonly referred to as "spike" pressures.

The above discussion assumes that the actuated valve spool was not shifted far enough out of neutral to establish a path for supply fluid to flow in a metered amount through its feeder passage 29 to a selected one of its associated ports 27, 28. After the valve spool is placed in such an operating position providing for fluid flow from its upstream to its downstream feeder passage portions through the throttle notches 36 in its land 35, the pressure in the unloading valve chamber 58 again will be increased by reason of the fact that the load is now added to the pressure already therein. Any fluid not demanded for delivery to the selected motor port, of course, is bypassed to tank through the unloading poppet 127, but now at said increased pressure.

It is to be observed that the fluid pressure in the unloading valve chamber 58 will always correspond to the predominating system pressure when two or more of the valve spools concurrently occupy working positions. The unloading valve, of course, will still bypass to tank any excess pump fluid at such times. The check valves 129 in the control lines 128 assure such operation of the unloading valve mechanism when a plurality of valve spools are in working positions.

The unloading poppet will also assume a fully closed position preventing bypass of pump fluid to tank when any one of the valve spools is actuated to a full operating position, as opposed to a metering position. At such a time, the demand for supply fluid causes full system pressure to be exerted in chamber 58, to hold the poppet closed.

If the valve spool in control section 111 is shifted to a full operating position such as described above, its priority type pressure compensated plunger P will move far enough to the left, in response to the pressure differential between its associated upstream and downstream feeder passage portions 31, 32, as to block flow of supply fluid from its supply branch 20 to the downstream branch 21 thereof, thereby assuring priority to the motor governed by control section 111. The parallel type pressure compensated plunger P1, in control section 110, can never block flow of supply fluid to the downstream control sections.

The control section 110 is provided with a simple but very effective stroke adjusting mechanism by which the movement of its valve spool toward each operating position thereof can be limited to the extent desired. This mechanism is readily accessible at one end of the spool, and it enables the maximum amount of fluid allowed to flow to either side of a reversible fluid motor via ports 27, 28 to be predetermined as desired.

For the above purposes, the cup-like housing 105 enclosing the spool centering spring mechanism is again provided with a screw threaded hole 107 in its outer end, coaxial with the valve spool. An elongated tubular member 140 is threaded into this hole and surrounds a stem 141 smaller in diameter than the valve spool but coaxially joined thereto and projecting therefrom to in effect provide an outwardly extending part of the spool. The stem can be connected to the spool in any desired fashion, for example by pinning its inner end portion in a coaxial outwardly opening well in the outer end of the spool, as at 142.

The opposite ends of the tubular member provide axially spaced apart stops 143, 144 which face in opposite directions, away from one another, and these can be considered as body carried stops which are adjustable in unison axially along the stem 141 by turning the tubular member farther into or out of the threaded hole 107 in the housing 105. A jam nut 146 threaded over the exterior of the tubular stop defining member 140 and bearing against the outer end of the housing 105 holds the member in the adjusted position desired.

The tubular member is located between a pair of inner and outer spool carried stops 147, 148, which are normally spaced from but engage one end or the other of the tubular member to define the limits of spool movement in either direction from its neutral position. The inner stop 147 is located at the outer end of the spool per se, and comprises a circumferential flange 150 on the spool which also cooperates with the centering spring mechanism when the spool is moved away from the tubular member 140, to yieldingly resist such movement. The outer spool carried stop 148 comprises a nut threaded onto the outer end portion of the stem 141, and held in the desired position of adjustment thereon by means of a jam nut 151. An elongated acorn type nut 152 is threaded over the exterior of the tubular member 140, outwardly of the jam nut 146 thereon, to enclose the threaded outer end portion of the stem 141 and the nuts thereon.

With the construction described, the spool carried flange 150 is engageable with the stop 143 provided by the inner end of the tubular member 140 to define the right hand limit of spool movement, while the nut 148 is engageable with the stop 144 provided by the outer end of the tubular member to limit motion of the spool in the opposite direction.

The tubular member is bodily adjustable axially relative to the housing 105 to provide for adjustment of the extent of spool movement to the right of neutral; and the nut 148 is adjustable along the stem 141 to provide for adjustment of the extent of spool movement to the left of neutral. When it is desired to change only the right hand operating stroke of the valve spool, it will be necessary to adjust the position of the tubular member 140 in the required direction and to also turn the nut 148 in the same direction and by the same amount in order to preserve the adjustment of the left hand stroke of the spool. The left hand stroke of the spool can be adjusted simply by turning the nut 148 in the required direction to the desired extent.

Another feature of the control valve illustrated in FIG. 7 resides in the provision of each of valve sections 111 and 112 with a void control check valve 291 which can be used with or without the conventional combined high pressure relief and void control check valves 91. One such void control check valve 291 governs a feedback passage 292 in valve section 111, leading from its left hand low pressure return passage 30 to the entrance 33 of the downstream feeder passage portion 32. It will be recalled, of course, that the entrance 33 to the downstream feeder passage portion is located in the bore 24, and hence upstream from the load holding check vale 34.

The other void control check valve 291 governs a feed back passage 293 in valve section 112, leading to its downstream feeder passage portion 32 at a location downstream from the load holding check valve 34 therein.

In either case, therefore, pressure fluid in the low pressure passage 30 can flow to the downstream feeder passage portion whenever the pressure in the latter is exceeded by that of return fluid in the low pressure passage, for void relief purposes.

FIG. 11 illustrates a modified pressure compensated control section 175 of the type which can be stacked with another control selection to provide for series operation of fluid motors governed by said control sections. It is to be understood that an unloading valve mechanism such as disclosed in the inlet section 113 described earlier will also be used with the control section 175.

As seen in FIG. 11, the upstream feeder passage portion 176 extends from the bore 41 of the pressure compensated plunger P to the bore 24 containing a valve spool 177 of special construction. The upstream feeder passage portion 176 intersects the bore 24 midway between the zones of intersection between the bore and the opposite ends of the bridge-like downstream feeder passage portion 32.

The valve spool has an imperforate middle portion, and it is formed with internal axially extending passages 178, 179 at each side of its imperforate middle portion. The ends of axial passage 178 join with crossbores 180, 181, while the end of axial passage 178 join with similar crossbores 182, 183. It will be readily understood that the axial passages would be drilled from the opposite ends of the valve spool, after which their outer ends would be plugged.

The outermost crossbores 180, 183, are disposed such as to communicate with the motor ports 27, 28, respectively, in the neutral position of the valve spool. In that position of the spool, the intermost crossbores 181, 182 open to the bore at zones which lie at opposite sides of its junction with the upstream feeder passage portion 176, between the latter and the ends of the bridge-like downstream feeder passage portion 32.

The spool is also provided with shallow circumferential grooves 185 which communicate with the outermost crossbores 180, 183 and extend a short distance axially inwardly therefrom. Also, that leg of the bridge-like downstream feeder passage portion 32 which is disposed adjacent to the motor port 28 is extended to communicate with the downstream supply passage branch 21.

With this arrangement, the valve spool can be shifted to the right of its neutral position shown to communicate its crossbore 181 with the upstream feeder passage portion 176, and thus provide for flow of supply fluid through axial passage 178 in the spool to motor port 27, into which it passes from the outer crossbore 180. Fluid expelled from the governed motor to motor port 28 flows into axial passage 179 in the spool via crossbore 183, and issues from crossbore 182 which is then in register with the downstream supply passage branch 21. Accordingly, fluid exhausting from the motor governed by spool 177 is delivered through supply passage branch 21 to the upstream branch 20 of the next downstream control section to be made available to one or the other of its motor ports under the control of the valve spool therein.

Shifting of the valve spool to the left of neutral communicates motor port 28 with the upstream feeder passage portion 176 via the internal passage 179 in the spool and its crossbores 182, 183. Pressure fluid can then flow to one side of a fluid motor connected with port 28, and fluid expelled from the other side of the motor is returned to motor port 27. The latter port is now in communication with the left hand end of the bridge-like downstream feeder passage portion 32, and motor exhaust fluid flows through the latter to the downstream supply passage branch 21 to be transferred thereby to the upstream supply passage branch 20 of the next downstream control section.

In this way, motor exhaust fluid is made available for operation of another fluid motor under the control of the valve spool in a downstream control section, regardless of whether the spool 177 in the series section is shifted to an operating position to the right or to the left of neutral.

It is to be understood, of course, that in this series flow embodiment of the invention, one or the other of the innermost crossbores 181, 182 can be placed in only partial register with the upstream feeder passage portion 176 to provide a throttle orifice between the feeder passage portions as before, through which the flow of pressure fluid to the selected motor port can be metered. The plunger P in the compensating valve mechanism will again function to accurately maintain the flow rate of fluid to the motor at a constant value determined by the size of the orifice connecting the feeder passage portions 176 and 32.

The pressure compensated plunger P is responsive to the pressure of fluid in the upstream feeder passage portion, and tends to be moved to the right by such pressure exerted on its left hand end, as before. The pressure of fluid in either motor port to which supply fluid is directed by the valve spool is imposed upon the right hand end of the plunger. For this purpose, a passageway 187 having one end in communication with the right hand actuating chamber 42 is provided with branches 188 and 189, as diagrammatically illustrated in FIG. 11, to communicate chamber 42 with either motor port to which pressure fluid is directed by the valve spool.

The branch passages 188, 189 open to enlargements 190, 191, respectively, of the bore 24 near the junctions of the latter with the motor ports 27, 28. Hence, the left hand spool groove 185 communicates motor port 27 with chamber 42 when the spool is shifted to the right to direct supply fluid to motor port 27. Similarly, the right hand spool groove 185 communicates motor port 28 with chamber 42 when the valve spool is shifted to the left to direct supply fluid to port 28.

A second enlargement 192 of the bore 24, communicating with the return venting passage 65' and located alongside of the enlargement 191 cooperates with the latter and with an adjacent grooved portion of the spool in the neutral position thereof, to establish a venting path for the compensating valve chamber 42. This path is closed, as before, when the valve spool is moved in either direction out of its neutral position. The passage 194 in the control section 175 leads to the unloading valve chamber, and it is communicated with the chamber 42 of the compensating valve through a check valve 132 in a linking passageway which can be provided by the grooved portion of the undersurface S of the control secton in the manner described hereinbefore.

From the foregoing description, together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides a pressure compensated control valve which operates in an exceptionally efficacious manner.

Those skilled in the art will appreciate that the invention can also be embodied in forms other than as herein disclosed for purposes of illustration.

Claims

The invention is defined by the following claims.

1. In combination with a control valve mechanism having pressure fluid inlet and outlet means and a valve element movable in a bore to an operating position at which supply pressure fluid from the inlet means can flow to a motor port via a feeder passage having portions upstream and downstream of the bore:

A. a flow control mechanism having a pressure sensitive valve plunger to regulate flow of supply fluid to said upstream feeder passage portion in accordance with variations in the pressure differential between said feeder passage portions;

B. an unloading valve separate from said flow control mechanism and having a fluid pressure actuatable valve member which is normally held in an open position by force which supply fluid exerts thereon to then communicate the inlet and outlet means;

C. and means operable as a consequence of movement of said control valve element to its operating position for imposing the pressure of fluid flowing to said motor port on said unloading valve member to move the same to a bypass closing position.

2. In combination with a control valve mechanism having a valve element movable from a neutral position to an operating position directing source fluid to a motor port along a path leading through the downstream portion of a feeder passage from an upstream feeder passage portion with which it communicates through the bore and an orifice whose size is set by the valve element, said upstream feeder passage portion comprising part of a supply passage which connects with an inlet for source fluid:

A. a flow control valve mechanism connected with the supply passage and operable to regulate flow of pressure fluid therefrom to said upstream feeder passage portion in accordance with variations in pressure drop across said orifice;

B. an unloading valve having a valve member movable in one direction to open a bypass for source fluid in response to force which the latter imposes upon one portion thereof at times when the valve element is in neutral, and movable in the opposite direction, toward a bypass closing position in response to fluid pressure force imposed upon another portion thereof;

C. and means for imposing fluid pressure closing force upon said other portion of the valve member, comprising duct means which leads to the unloading valve from a portion of said path that is upstream from said orifice.

3. The combination of claim 2, further characterized by a load check valve in said downstream feeder passage portion, said check valve at all times preventing flow of motor exhaust fluid in the motor port to said duct means.

4. The combination of claim 2, further characterized by:

A. said unloading valve member operating in a chamber and its movement toward bypass closing position depending upon closure of a venting passage for said chamber;

B. and means for effecting closure of said venting passage and to assure such closure thereof at the time said feeder passage portions are communicated with one another by the valve element.

5. The combination of claim 4 wherein said duct means leads to the unloading valve chamber from said inlet.

6. The combination of claim 4, wherein said duct means leads to the unloading valve chamber from the upstream feeder passage portion.

7. A control valve mechanism having pressure fluid inlet and outlet means, and comprising the combination of:

A. an unloading valve which, when open, communicates the inlet and outlet means, and having a chamber with a fluid pressure responsive valve member therein yieldingly urged to a valve closed position but movable under force exerted thereon by inlet fluid to an open position, providing that a venting passage for said chamber is open;

B. a plurality of control valves downstream from the unloading valve, each having a bore, a motor port, a feeder passage with portions disposed both upstream and downstream of said bore and through which pressure fluid flows to said port, and a valve element movable from a neutral position to an operating position directing pressure fluid through the feeder passage to the motor port;

C. said venting passage serially intersecting said bores to be closed by the valve element in any one of them upon movement thereof from its neutral position to said operating position thereof;

D. and a flow control valve for each of said control valves, having a supply passage for connecting the upstream feeder passage portion of the associated control valve with the inlet means.

8. The control valve mechanism of claim 7, wherein pressure fluid from the inlet means flows into said unloading valve chamber to hold the valve member thereof closed when said venting passage is closed.

9. The control valve mechanism of claim 7, wherein said chamber of the unloading valve is connected with the upstream feeder passage portion of each of said control valves so that pressure fluid from any one of said upstream feeder passage portions can flow into said chamber and apply closing force to the valve member therein at times when its associated valve element closes said venting passage.

10. The control valve mechanism of claim 7, further characterized by:

A. a control pressure line connecting each of said upstream feeder passage portions with the unloading valve chamber;

B. and a check valve in each of said control pressure lines.

11. The control valve mechanism of claim 7, further characterized by:

A. passage means providing for flow of pressure fluid from the inlet means serially through said flow control valves to the supply passage of each;

B. and a fluid pressure sensitive plunger in each flow control valve actuatable in a direction to increase flow to the upstream feeder passage portion of the associated control valve in response to decrease in the pressure differential between said feeder passage portions of its associated control valve.

12. A control valve mechanism having pressure fluid inlet and outlet means, and comprising the combination of:

A. a control valve having a body with a bore and a valve element shiftable axially in the bore from a neutral position to an operating position to communicate a motor port with a feeder passage having portions upstream and downstream from the bore with a load holding check valve in said downstream feeder passage portion;

B. a flow control valve having a supply passage to connect said upstream feeder passage portion with the inlet means and having a fluid pressure actuatable plunger to control flow of fluid from the supply passage to said upstream feeder passage portion;

C. means for translating the pressure of fluid in the supply passage into force on said plunger tending to move it in the direction to decrease said flow to the upstream feeder passage portion;

D. means for translating the pressure of fluid in said downstream feeder passage portion into force on the plunger tending to move it in the direction to increase said flow to the upstream feeder passage portion, said last named means comprising a signal passageway in the body connecting with an actuating chamber in which one end portion of the plunger is received and with the downstream feeder passage portion at a location ahead of said check valve;

E. and an unloading valve upstream from the flow control valve, to communicate the inlet means with the outlet means except at times when said valve element is moved to an operating position.

13. The control valve mechanism of claim 12, further characterized by:

A. said flow control valve being accommodated in the body of the control valve;

B. said valve mechanism being of sectional construction wherein said body comprises one section of a bank and is confined between two other sections of the bank with opposite surfaces of the body in intimate engagement with mating surfaces on said other sections;

C. and a portion of said signal passageway being provided by a groove in one surface of the body.

14. The control valve of claim 13, wherein said unloading valve is accommodated in one of said other sections.

15. A pressure compensated sectional control valve mechanism comprising a pair of end sections and one or more valve sections confined between said end sections with flat faces thereof in intimate engagement with mating faces of adjoining sections, characterized by:

A. one of said end sections having an inlet to receive supply fluid from a pump;

B. each of said valve sections having a bore, feeder and motor passages opening to the bore, and a valve element movable in the bore from a neutral position to an operating position to provide for flow of pressure fluid from the feeder passage to the motor port, said feeder passage having portions disposed both upstream and downstream of the bore;

C. a flow control valve mechanism in each valve section comprising a bore the opposite ends of which define pressure chambers, a supply passage to communicate the inlet means with the upstream feeder passage portion of the associated valve section, and a fluid pressure responsive plunger in the bore with its ends in said chambers to be acted upon by pressure fluid therein, and operable to control fluid flow from the supply passage to the upstream feeder passage portion;

D. means communicating one of said chambers of each flow control valve with the upstream feeder passage portion of its associated valve section;

E. duct means communicating the other chamber of each flow control valve with the downstream feeder passage portion of its associated valve section, including a groove in one face of said valve section;

F. and an unloading valve mechanism in one of said end sections having a bypass rendered operative to communicate the inlet means with a return port when the valve elements in all of said valve sections are in their neutral positions.

16. The control valve mechanism of claim 15, further characterized by:

A. the supply passage of each flow control valve mechanism being communicable with that of an adjoining flow control valve mechanism downstream from the inlet means through a supply passage branch under the control of the plunger in the upstream flow control valve mechanism;

B. and each plunger being operable to restrict fluid flow to its supply passage branch to a degree depending upon the extent of plunger movement under the influence of pressure in said other chamber thereof.

17. The control valve mechanism of claim 16, wherein the supply passage branch of the flow control valve mechanism farthest from the inlet means communicates with a return port.

18. A pressure compensated control valve mechanism having an inlet, an outlet and a plurality of valve spools each movable axially in a bore from a neutral position to an operating position to provide for flow of pressure fluid to a motor port from a feeder passage having portions upstream and downstream from the bore and communicable therethrough, characterized by:

A. means providing an elongated supply passage which is connected with the inlet and which extends serially past all of said bores, in spaced relation thereto;

B. a plurality of flow controlling mechanisms, one for each of said upstream feeder passage portions to supply fluid thereto via a branch of the supply passage, each flow controlling mechanism having a fluid pressure actuatable plunger to regulate fluid flow to its upstream feeder passage portion in accordance with variations in the pressure differential between its upstream and downstream feeder passage portions;

C. an unloading valve mechanism upstream from said flow controlling mechanisms, having a pressure sensitive valve member actuatable to an open position communicating the inlet with the outlet in response to inlet fluid pressure, providing a chamber in which said valve member operates is vented;

D. and a venting passage for said chamber serially intersecting all of said bores so as to be closed by the valve spool in any one of them upon movement thereof to its operating position.

19. a pressure compensated sectional control valve mechanism having at least one control section confined between end sections with mating faces on the sections in intimate engagement, characterized by:

A. each control section having a valve spool slidable axially in a bore from a neutral position to an operating position to provide for flow of pressure fluid to a motor port from a feeder passage having portions disposed both upstream and downstream of the bore;

B. means providing inlet and return passages;

C. a supply passage connecting with the inlet passage and extending into each valve section, said supply passage having a branch in each valve section through which supply fluid can flow to the upstream feeder passage portion thereof;

D. a flow controlling mechanism in each control section having a plunger to regulate said flow through the associated supply passage branch in accordance with variations in the pressure differential between said feeder passage portions of its associated valve section;

E. means by which the pressure obtaining in the upstream feeder passage portion of each valve section is imposed on one end of the plunger of the associated flow control mechanism;

F. and duct means by which the pressure obtaining in the downstream feeder passage portion of each valve section is imposed on the other end of the plunger of the associated flow control mechanism, including a groove in one face of each valve section.

20. A pressure compensated control section for a stacked valve, characterized by the following:

A. a body having opposite surfaces to intimately engage mating surfaces on adjoining sections of a stacked valve, and a bore intersected by a motor passage and a feeder passage which has upstream and downstream portions that are communicable with one another through the bore;

B. a valve spool slidable axially in the bore to an operating position communicating said downstream feeder passage portion with the upstream feeder passage portion and with the motor port;

C. a carryover supply passage portion in the body opening to said opposite surfaces thereof, through which supply fluid under pressure can pass from said section to an adjoining section of a stack thereof;

D. a flow control valve mechanism in the body comprising;

1. a bore with which said supply and feeder passage portions communicate, and which has opposite end portions that provide actuating chambers,

2. and a pressure sensitive plunger slidable axially in the bore to regulate flow of fluid from said supply passage portion to said upstream feeder passage portion in accordance with the pressure differential between said feeder passage portions;

E. and means for subjecting the flow control plunger to said pressure differential, comprising;

1. holes in the body which open at one end to spaced zones of one of said body surfaces, one of said holes connecting with one of said actuating chambers, and the other of said holes connecting with the downstream feeder passage portion at the bore containing the valve spool,

2. and a groove in said one body surface communicating said first designated ends of the holes.

21. A pressure compensated control valve mechanism having a body with a pressure fluid inlet, a plurality of valve spools each movable axially in a bore to an operating position to provide for flow of inlet pressure fluid through a supply passage to a motor port via a feeder passage having portions upstream and downstream from the bore and communicable therethrough, characterized by the following:

A. a flow controlling plunger for each feeder passage, to regulate flow to the upstream portion of the latter from the supply passage in accordance with variations in the pressure differential between said feeder passage portions;

B. a bore for each of said plungers, in which the plunger operates;

C. said supply passage leading from the inlet serially through said plunger bores;

D. and means on one of said plungers to assure flow of pressure fluid to the adjacent downstream plunger bore regardless of the position of said one plunger.

22. A pressure compensated control valve mechanism having a body with inlet and return passages, a pair of motor ports, and a valve spool movable in a bore from a neutral position to each of a pair of operating positions to provide for connection of either motor port with the return passage and the other motor port with an inlet connected supply passage via a feeder passage having a portion upstream from the bore and another portion downstream from the bore in the direction of flow to said motor ports and common to the latter, characterized by the following:

A. a flow control mechanism having a fluid pressure responsive plunger which operates in a bore alongside the valve spool and regulates flow from the supply passage to said upstream feeder passage portion in accordance with variations in the pressure differential between said feeder passage portions;

B. an unloading valve mechanism separate from said flow control mechanism, having a pressure sensitive valve member to communicate the inlet and return passage providing a venting passage for the unloading valve mechanism is open;

C. means comprising land means on the spool operable, upon movement of the spool from its neutral position to either operating position thereof to close said venting passage and effect movement of said unloading valve member to a position blocking communication between the inlet and return passages;

D. and said supply passage communicating with the return passage only through said bypass, whereby pressure fluid in the supply passage in excess of that flowing through the feeder passage to a selected motor port will flow to the return passage through the unloading valve.

23. The pressure compensated control valve mechanism of claim 22, further characterized by:

A. said unloading valve having a chamber in which its valve member operates and from which said venting passage leads;

B. the venting passage extending through said bore being open in the neutral position of the spool but closed by the said land means on the spool in either operating position thereof;

C. and means communicating said unloading valve chamber with said upstream feeder passage portion so as to effect closing motion of the unloading valve member under force which depends upon the pressure in the feeder passage.

24. In a closed center pressure compensated control valve mechanism having a body with inlet and return passages, a pair of motor ports, and a valve spool movable in a bore from a neutral position to each of a pair of operating positions to provide for flow selectively to said motor ports of pressure fluid from an inlet connected supply passage via a feeder passage having an orifice therein the size of which depends upon the extent the valve spool is displaced from its neutral position, and a load check valve downstream from said orifice:

A. an unloading valve mechanism having a fluid pressure responsive valve member to govern a bypass between the inlet and return passages and which is urged in the bypass closing direction by a substantially light spring force that can be easily overcome by force which inlet fluid exerts thereon;

B. a flow control mechanism having a valve plunger to regulate flow of pressure fluid from the supply passage to the feeder passage in accordance with variations in the pressure drop across said orifice;

C. and means rendered effective by the valve spool in one operating position thereof to translate the pressure of fluid obtaining in the feeder passage at a location upstream from said load check valve into additional force on the unloading valve member tending to move it in the bypass closing direction.

25. The closed center valve mechanism of claim 24, wherein said last named means is effective in either operating position of the valve spool.

26. A pressure compensated control valve mechanism having a body with inlet and return passages, a pair of motor ports, and a valve spool movable in a bore from a neutral position to each of a pair of operating positions to provide for connection of either motor port with the return passage and the other motor port with the inlet passage via a feeder passage having portions upstream and downstream of the bore and communicable therethrough with one another, characterized by:

A. an unloading valve having a bypass through which inlet fluid can flow to the return passage and having a pressure sensitive valve member movable in a chamber to open the bypass under force exerted on the valve member by inlet fluid, and movable toward bypass closing position under substantially light spring force as well as under force exerted thereon by pressure fluid in said chamber;

B. means providing a venting passage for said chamber, which venting passage is ordinarily open but is closed by the valve spool in either operating position thereof;

C. a flow control valve mechanism having a plunger to regulate flow of pressure fluid from the inlet passage to said upstream feeder passage portion in accordance with variations in the pressure differential between said feeder passage portions, said plunger being urged toward a position providing substantially free fluid flow to the feeder passage by a spring substantially stronger than said unloading valve spring;

D. and means rendered effective in either operating position of the valve spool to subject the unloading valve chamber to the pressure of fluid in said upstream feeder passage portion thereby to augment the spring force tending to move said unloading valve member in the bypass closing direction.

27. The pressure compensated control valve of claim 26, further characterized by:

A. said control valve being of sectional construction having at least one spool section confined between adjacent sections with oppositely facing surfaces on said spool section in intimate mating engagement with surfaces on adjoining sections;

B. said unloading valve being housed in a section closer to the inlet than said spool section;

C. and said means for pressurizing the unloading valve chamber comprising

1. a first passageway which extends from said chamber through the spool section and opens to one of said surfaces thereof at a first zone,

2. a second passageway which extends from said upstream feeder passage portion to said one surface of the spool section at a second zone spaced from the first,

3. and a groove in said one surface connecting said passageways.

28. The pressure compensated control valve of claim 27, wherein said second passageway opens to said surface through a counterbore which defines a valve seat, and a check valve member is confined in said counterbore for cooperation with said seat, and is held against displacement from its counterbore by the mating surface on the adjoining section.

29. In a pressure compensated control valve mechanism having a body with inlet and return passages, a supply passage connecting with the inlet passage, and a plurality of valve spools each movable axially in a bore from a neutral position to two operating positions to provide for flow of pressure fluid from the supply passage selectively to either of a pair of motor ports via a feeder passage having portions upstream and downstream of the bore and communicable therethrough:

A. an unloading valve mechanism connected with the inlet and return passages and operable to establish communication therebetween when all of the valve spools are in their neutral positions;

B. a flow controlling mechanism for each spool, having a valve plunger movable axially in a bore to regulate fluid flow from the supply passage to the associated upstream feeder passage portion in accordance with variations in the pressure differential between said feeder passage portions;

C. said supply passage having inlet and outlet branches intersecting the bore of each flow controlling mechanism at axially spaced zones and communicable with one another under the control of the plunger therein, each of said outlet branches comprising the inlet branch for the next downstream flow controlling mechanism;

D. means on each plunger to control fluid flow from its inlet to its outlet supply passage branch;

E. and means governed by at least one of said valve spools for conducting motor return fluid from one of its associated motor ports to the outlet supply passage branch of its associated flow controlling mechanism.

30. The pressure compensated control valve mechanism of claim 29, wherein said one valve spool directs return fluid from either of its motor ports to the outlet supply passage branch of its associated flow controlling mechanism.

31. The pressure compensated control valve of claim 29, further characterized by:

A. said unloading valve mechanism having a pressure actuatable valve member to govern a bypass between the inlet and return passages, and which valve member is urged by a substantially light spring force toward a bypass closing position;

B. and means operable in an operating position of one of said valve spools for translating the pressure of fluid obtaining in its associated upstream feeder passage portion into additional force on the unloading valve member tending to move it in the bypass closing direction.

32. In combination with a control valve having a high pressure inlet passage for pump fluid, an outlet passage, a pair of motor ports, and a valve spool movable from one operating position to another to in turn communicate each motor port with the inlet passage and the other motor port with a low pressure passage:

A. means to communicate said low pressure passage with the outlet passage comprising a low pressure relief valve which opens in response to rise in pressure in said low pressure passage to a predetermined value above that of pressure fluid in the outlet passage;

B. means including an anti-void valve through which fluid in said low pressure passage can flow to one of said motor ports whenever fluid pressure in the latter drops below the pressure of fluid in said low pressure passage;

C. means providing a void relief passage through which pressure fluid can flow from said high pressure inlet passage to the low pressure passage;

D. and a pressure sensitive valve member to govern said flow of fluid through the void relief passage, said valve member being movable to a passage closed position in response to rise in pressure in said low pressure passage to a value above that of fluid in said outlet passage but below said predetermined value.

33. The combination of claim 32, wherein fluid in the low pressure passage can flow to either of said motor ports through an anti-void valve for each.

34. An inlet section for a stacked control valve, characterized by a body having:

A. a flat surface to mate with a similar surface on an adjoining section of the valve;

B. means defining a fluid supply passage which opens to said surface on the body;

C. means defining a return passage through which fluid expelled from a controlled motor can flow to an exhaust outlet;

D. means defining a low pressure passage which opens to said surface on the body and through which exhaust fluid from a controlled motor must flow to reach said return passage;

E. a passageway to provide for flow of fluid from the low pressure passage to the return passage;

F. a low pressure relief valve which permits such flow when pressure in the low pressure passage reaches a predetermined relief value;

G. another passageway to provide for flow of fluid from the supply passage to said low pressure passage;

H. a valve member governing said flow through said other passageway and normally held in a flow preventing position by fluid pressure in the low pressure passage;

I. and a spring acting on said valve member to move the same to a flow permitting position whenever fluid pressure in the low pressure passage drops to a value substantially less than said predetermined relief value.

35. The inlet section of claim 34, further characterized by an unloading valve in the body to govern flow of fluid through a bypass leading to the return passage from the supply passage.

36. A control valve mechanism, characterized by:

A. a body having a bore with a valve spool movable therein from a neutral position to an operating position to provide for flow of pressure fluid from a supply passage to a motor port via a feeder passage having portions upstream and downstream of the bore;

B. a flow control mechanism in the body having a valve plunger to regulate fluid flow from the supply passage to said upstream feeder passage portion in accordance with variations in the pressure differential between said feeder passage portions;

C. a portion of said bore defining the entrance to said downstream feeder passage portion;

D. means in the body defining a reservoir passage which opens to the bore;

E. and means on the valve spool rendered effective in the neutral position thereof to communicate said bore portion with the resevoir passage.

37. A control valve mechanism, characterized by:

A. a body having a bore with a valve spool movable therein from a neutral position to an operating position to provide for flow of pressure fluid from a supply passage to a motor port via feeder passage means having portions upstream and downstream of the bore communicable with one another through an orifice;

B. means providing a flow control mechanism having a fluid pressure responsive plunger to regulate flow of fluid from the supply passage to the upstream feeder passage portion in accordance with variations in the pressure differential across said orifice;

C. a load holding check valve in said downstream feeder passage portion and spaced from the bore;

D. means in the body defining a reservoir passage the mouth of which opens to said bore;

E. and means on the valve spool for communicating that portion of the bore which is upstream from said check valve but at the downstream side of said orifice, with the mouth of the reservoir passage in the neutral position of the valve spool.

38. A control valve mechanism for a reversible fluid motor, comprising the combination of:

A. an unloading valve having inlet and return passages, a bypass to normally communicate the same, and a chamber with a fluid pressure responsive valve member therein movable to a bypass closing position in consequence of closure of a venting passage for said chamber;

B. a flow control valve separate from the unloading valve, having a supply passage connecting with said inlet passage and from which pressure fluid can flow to one side or the other of a fluid motor via a feeder passage having an orifice therein, said flow control valve having a fluid pressure responsive plunger adapted to regulate fluid flow from the supply passage to the feeder passage in accordance with variations in the pressure differential across said orifice;

C. and a directional control valve having a bore which is intersected by said feeder passage and a valve spool movable in the bore from a neutral position to first and second operating positions to in turn communicate each of a pair of motor ports with the feeder passage, said spool having means thereon to provide said orifice and to adjust the size thereof in accordance with the extent the spool is displaced from neutral;

D. a venting passage for said unloading valve chamber, leading through said bore to be closed by the spool therein when the spool is moved out of its neutral position;

E. and means rendered effective in a third operating position of the spool to communicate both motor ports with the feeder passage.

39. A control valve mechanism for a reversible fluid motor, comprising the combination of:

A. an unloading valve having inlet and return passages, a bypass to normally communicate the same, and a chamber with a fluid pressure responsive valve member therein movable to a bypass closing position in consequence of closure of a venting passage for said chamber;

B. a flow control valve separate from the unloading valve, having a supply passage connecting with said inlet passage and from which pressure fluid can flow to one side or the other of a fluid motor via a feeder passage having an orifice therein, said flow control valve having a fluid pressure responsive plunger to regulate fluid flow from the supply passage to the feeder passage in accordance with variations in the pressure differential across said orifice;

C. and a directional control valve having a bore which is intersected by said feeder passage, and a valve spool movable in the bore from a neutral position to first and second operating positions to in turn communicate each of a pair of motor ports with the feeder passage and the other motor port with a low pressure passage for return fluid, said spool having means thereon to provide said orifice and to adjust the size thereof in accordance with the extent the spool is displaced from neutral;

D. a venting passage for the unloading valve chamber, leading through said bore to be closed by the spool upon movement thereof out of its neutral position;

E. and means rendered effective in a third operating position of the spool to communicate said motor ports with one another through portions of the feeder passage downstream of the bore and to also communicate one of said motor ports with the low pressure passage for return fluid.

40. In combination with a control valve having a high pressure inlet passage for pump fluid, an outlet passage, a pair of motor ports, a valve spool movable in a bore from first to second operating positions to in turn communicate each motor port with a low pressure passage and the other motor port with the inlet passage via a feeder passage having a portion which communicates with the bore downstream thereof from the inlet passage and which is common to both motor ports:

A. a low pressure relief valve through which said low pressure passage is communicable with the outlet passage;

B. means providing a void relief passage through which pressure fluid can flow from the low pressure passage to said common portion of the feeder passage;

C. and a void relief valve governing flow through said void relief passage and actuatable to a passage open position by pressure of fluid in said low pressure passage at times when pressure therein exceeds that in either motor port then in communication with the inlet passage.

41. A control valve having a body and a valve spool which is movable from a neutral position to operating positions at opposite sides of neutral to provide for flow of pressure fluid to one or the other of a pair of motor ports in an amount depending upon the extent the spool is displaced from its neutral position, characterized by:

A. means on the spool at one end portion thereof defining a pair of axially spaced apart stops;

B. means on the body adjacent to said end portion of the spool defining a pair of stops which are spaced apart lengthwise of the spool axis;

C. the stops of one pair facing toward one another;

D. the stops of the other pair facing away from one another and being disposed between the stops of said one pair with each stop of said other pair in spaced confronting relation to one of the stops of said one pair in the neutral position of the spool, whereby said stops cooperate to limit motion of the spool in each direction out of its neutral position;

E. and means providing for axial adjustment of one of said stops so as to enable spool movement in one direction from its neutral position to be halted at any of a number of positions determined by the adjustment of said one stop.

42. The control valve of claim 41, further characterized by means providing for axial adjustment of two of said stops so as to enable spool movement in each direction from its neutral position to be halted at positions determined by the adjustment of said two stops.

43. The control valve of claim 42, further characterized by:

A. the stops on the spool facing one another and comprising a fixed stop and an axially adjustable stop;

B. and the stops on the body comprising the ends of a tubular member which concentrically encircles said end portion of the spool between the stops thereon, and which is bodily adjustable axially relative to the spool carried stops.

44. The control valve of claim 43, further characterized by:

A. said end portion of the spool projecting from one end of the body;

B. a centering spring assembly carried by the body at said end thereof and acting on the spool to yieldingly resist motion thereof out of its neutral position, said assembly including a housing encircling said end portion of the spool and having an internally threaded hole concentric with the spool axis;

C. said tubular member being threaded in said hole so as to be adjustable relative to the body;

D. said axially fixed stop on the spool facing outwardly away from the body and comprising a flange upon which the spring in the centering spring assembly acts to resist motion of the spool in the direction to carry said fixed stop away from the tubular member;

E. means providing a reduced extension on said end portion of the spool which extends through the interior of said tubular member and beyond the outer end thereof;

F. and said other stop on the spool comprising a nut threaded on the outer extremity of said spool extension.

45. The control valve of claim 44, further characterized by:

A. a locknut threaded onto the exterior of said tubular member and bearing against said centering spring housing;

B. and a cover threaded over the outer end portion of the tubular member and bearing against said locknut, said cover enclosing the outer end portion of the spool extension and the nut thereon.

46. In combination with a control valve mechanism having pressure fluid inlet and outlet means and a valve element movable in a bore to an operating position at which pressure fluid can flow to a motor port via a feeder passage having a portion downstream of the bore and another portion upstream of the bore, and comprising part of a supply passage that communicates with the inlet means:

A. a flow control mechanism having a pressure actuatable valve plunger sensitive to the pressure differential between said feeder passage portions to regulate flow of fluid through said supply passage in accordance with variations in said pressure differential;

B. an unloading valve separate from said flow control mechanism and having a fluid pressure actuatable valve member which is normally held in an open position communicating the inlet means with the outlet means by force which fluid in the supply passage exerts thereon;

C. and means operable as a consequence of movement of said control valve element to said operating position thereof for translating the pressure of fluid in the supply passage into closing force on said unloading valve member.

47. In combination with a control valve mechanism having pressure fluid inlet and outlet means and a valve element movable in a bore to an operating position at which pressure fluid from the inlet means can flow to a motor port via a feeder passage having a portion upstream of the bore and another portion downstream of the bore to receive pressure fluid therethrough from said upstream portion:

A. a flow control mechanism having an inlet connected with said inlet means, an outlet connected with said upstream feeder passage portion, and a pressure actuatable valve plunger sensitive to the pressure differential between said feeder passage portions to regulate flow of pressure fluid from its inlet to its outlet in accordance with variations in said pressure differential;

B. an unloading valve having a fluid pressure actuatable valve member which is normally held in an open position communicating said inlet and outlet means by force which fluid from the inlet means exerts thereon;

C. and means operable as a consequence of movement of said control valve element to said operating position thereof for translating the pressure of fluid obtaining in the feeder passage into closing force on the unloading valve member.

48. The combination of claim 47, further characterized by:

A. a load check valve in said feeder passage;

B. and said last named means comprising duct means which leads to the unloading valve from a portion of the feeder passage upstream from said check valve so that the latter at all times prevents flow of motor exhaust fluid in said motor port to said duct means.

49. A control valve mechanism having a body with inlet and return passages, and a valve spool movable in a bore to each of a pair of operating positions to provide for connection of either of a pair of motor ports with the return passage and the other motor port with an inlet connected supply passage via a feeder passage having a portion upstream from the bore and another portion downstream from the bore in the direction of fluid flow to the motor ports and common thereto, characterized by the following:

A. a flow control mechanism in the body having a bore which is communicated with said upstream feeder passage portion and with the supply passage, and a plunger in said bore operable to regulate fluid flow from the supply passage to the upstream feeder passage portion in accordance with variations in the pressure differential between said upstream and downstream feeder passage portions;

B. and a load holding check valve in the body arranged to permit fluid flow from the upstream feeder passage portion to the downstream feeder passage portion and said motor ports, but to block reverse flow of fluid from the motor ports to said downstream feeder passage portion.

50. A control valve mechanism having a body with inlet and return passages, and a plurality of valve spools each movable in a bore to each of a pair of operating positions to provide for connection of either of a pair of associated motor ports with the return passage and the other of said associated motor ports with an inlet connected supply passage via a feeder passage having a portion upstream from the bore and another portion downstream from the bore in the direction of fluid flow to said associated motor ports and common thereto, characterized by the following:

A. a plurality of flow control mechanisms in the body, one for each valve spool and at the upstream side thereof, each of said flow control mechanisms having a bore which is intersected by the supply passage and by the associated upstream feeder passage portion, and a plunger in said bore operable to regulate fluid flow from the supply passage to the associated upstream feeder passage portion in accordance with variations in the pressure differential between the associated upstream and downstream feeder passage portions;

B. and a plurality of load check valves in the body, one for the pair of motor ports associated with each valve spool and arranged to open to permit flow of fluid to either of said motor ports from the associated downstream feeder passage portion.