Arrangement For Pumping A Filtered Fluid

Abstract

A feed pump supplies a fluid through a filter to a main pump which pumps the fluid in filtered condition to a consumer. When the filter becomes clogged, a valve responsive to the increased pressure differential upstream and downstream of the clogged filter, supplies fluid for operating either a control valve connecting the outlet and inlet of the main pump and causing idle circulation of the fluid, or a hydraulic regulating means for setting the main pump to a minimum discharge.

Description

BACKGROUND OF THE INVENTION

Apparatus is known for filtering a fluid supplied by a feed pump through a filter to a main pump connected with a consumer conduit. In accordance with the prior art, a bypass valve is provided which, when the filter is clogged, or the fluid is a viscous liquid, particularly in cold condition, directs unfiltered fluid to the main pump. When unfiltered fluid is pumped by the main pump, particularly a piston pump, great wear occurs, and frequently the main pump fails.

SUMMARY OF THE INVENTION

It is the main object of theinvention to provide an arrangement in which only filtered fluid can be pumped by a main pump to a consumer.

Another object of the invention is to prevent operation of the main pump when the filter is in a faulty condition.

Another object of the invention is to use a high pressure differential occurring in a faulty condition of the filter, for operating control means which prevent the operation of the main pump with unfiltered fluid.

Another object of the invention is to provide pressure operated control means which control the flow of fluid through the filter to the main pump depending on the pressure differential occurring at the filter.

In this manner, an unfiltered flow of fluid from the feed pump to the main pump is prevented, so that the span of life of the main pump is substantially increased. The arrangement of the invention is operative when the filter is clogged by dirt filtered out of the fluid passing through the filter, and also when the fluid is a viscous liquid, as may occur when the pumps are started in cold condition of the fluid, or both faulty conditions may simultaneously occur.

An embodiment of the invention comprises a main pump and a consumer conduit through which the main pump discharges a fluid supplied by a feed pump through a feed conduit means including a filter having a working condition causing a normal pressure differential in the feed conduit; pressure responsive means, preferably including a pressure responsive valve, connected with the feed conduit upstream and downstream of the filter, and being in a normal inoperative position when the normal pressure differential indicates the working condition of the filter; and control means for the main pump means.

The pressure responsive means moves to an actuating position in response to a predetermined pressure differential different from the normal pressure differential, and indicating a faulty filtering action of the filter. The control means terminate discharge through the comsumer conduit by the main pump when the fluid supplied by the pressure responsive means in the actuated position operates the control means.

In one embodiment of the invention, the main pump pumps a constant amount of fluid, and discharge into the consumer conduit is prevented by a control valve causing idle circulation of the fluid pumped by the main pump.

In another embodiment of the invention, regulating means are provided for the main pump, and are operated by fluid by the pressure responsive means to reduce the output volume of fluid of the main pump when a high pressure differential at the filter indicates a faulty condition of the same.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic and diagrammatic view illustrating a first embodiment of the invention;

FIG. 2 is a schematic and diagrammatic fragmentary view illustrating a second embodiment of the invention in which the output of the main pump is regulated;

FIG. 3 is a schematic and diagrammatic view illustrating a third embodiment of the invention; and

FIG. 4 is a schematic and diagrammatic view illustrating a fourth embodiment of the invention in which the output of the main pump is automatically regulated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment 11 shown in FIG. 1 has a feed pump 12 which pumps a fluid through a feed conduit having an upstream portion 13 and a downstream portion 15 between which a filter 14 is located, so that the fluid supplied by feed pump 12 through the feed conduit 13,15 and filter 14 to the inlet of a main pump 16 is continuously filtered. Main pump 16 is driven, together with feed pump 12 by a prime mover, not shown, and pumps the fluid into a consumer conduit 17a, 17 connected with consumer apparatus 18, such as hydraulic motors. A control valve 37 is provided between the conduit portions 17a and 17 of the consumer conduit.

A first discharge conduit 19 branches off the feed conduit portion 13 upstream of filter 14, and discharges into a reservoir 21 which may be connected with the inlet of feed pump 12. A schematically illustrated pressure responsive valve 22, located in the discharge conduit 19, includes a schematically shown valve member 24 shiftable between a normal inoperative position and an actuated position. A spring 23 abutting the valve casing, biasses valve member 24 to a normal inoperative position 25 in which discharge conduit 19 is closed, and in which a first control conduit 26 is separated from the conduit 19 and feed conduit portion 13. Valve 22 is constructed similar to valve 97 shown in FIG. 4.

A control channel 19" connects conduit 19 and the feed conduit portion 13 upstream of filter 14 with one end of the casing of valve 22 to exert a pressure opposing the pressure of spring 23 on valve member 24. Another channel 19' connects a discharge conduit 28, and the feed conduit portion 15 downstream of filter 14 with the other end of the casing of pressure responsive valve 22 so that the pressure in channel 19' is added to the force of spring 23 and urges the valve member 24 into the normal inoperative position.

When the filter is in good working condition, and its flow resistance is low, the pressure differential between channels 19' and 19" is small, and insufficient for overcoming the force of spring 23 so that all the fluid pumped by feed pump 12 passes through the filter 14 to the main pump 16. However, when the filter is clogged, and its flow resistance is high, the pressure differential is increased, and the force exerted by the pressure fluid in channel 19" is sufficient to move valve member 24 to a second actuated position schematically indicated at 27, in which the fluid pumped by feed pump 12 into feed conduit portion 13 is discharged through discharge conduit 19 into the reservoir 21, and also through a first control conduit 26 to flow to a control valve 37 located in the consumer conduit between consumer conduit portions 17a and 17.

The second discharge conduit 28 branches off the feed conduit portion 15 and has a discharge outlet opening into reservoir 21. A pressure limiting valve 29 is provided in discharge conduit 28, and includes a movable valve member 32 urged by a spring 31 to a first position 33 closing discharge conduit 28, and also a second control conduit 34 which is connected to the control valve 37. The casing of pressure limiting valve 29 is connected at one end with channel 19' which is connected to the downstream portion 15 of the feed conduit, and acts on the valve member 32 of the pressure limiting valve 29 in a direction opposite to the force of spring 31. When the pressure is sufficiently high in channel 19' due a good condition of filter 14, the spring force of spring 31 is overcome, and valve member 32 moves to a second position 35 in which fluid from feed conduit portion 15 is supplied through discharge conduit 28 and a duct in valve member 32 to the second control conduit 34. If the pressure further increases, the valve member 32 moves to a third position 36 in which the second control conduit 34 is connected with the feed conduit portion 15, as before, but in which the discharge conduit 28 is connected with the discharge outlet into reservoir 21 so that the pressure in the second control conduit 2 cannot become excessively high.

The control valve 37 between the consumer conduit portions 17a and 17, has a movable valve member 39 urged by spring 38 to a control position 41 in which consumer conduit portion 17a is connected with a return or bypass conduit 42 which is connected to feed conduit portion 15 downstream of filter 14 and thereby with the inlet of main pump 16 so that in the position of the control valve 37 shown in FIG. 1, the main pump 16 idly circulates the fluid supplied by the feed pump 12, and no fluid flows through the consumer conduit portion 17 to the consumer apparatus 18.

The first control conduit 26 has a port in valve casing of valve 37 so that the fluid pressure in control conduit 26 acts on valve member 39 to move to the illustrated control position 41. The second conduit 34 is connected to the other end of the casing of control valve 37 and urges valve member 39 in the direction opposite to the force of spring 38 to an inoperative position in which the consumer conduit portions 17a and 17 are directly connected, and the main pump 16 discharges fluid through consumer conduit 12,17 to consumer apparatus 18.

The embodiment of FIG. 1 operates as follows.

The feed pump 12 supplies fluid through filter 14 and the feed conduit 13,15 to the inlet of the main pump 16 whose output discharges a constant volume of fluid. The output volume of feed pump 12 is always slightly greater than the absorption volume of the main pump 16, so that a certain filling pressure prevails in the feed conduit portion 15 determined by the pressure limiting valve 29. This filling pressure has the effect that valve member 32 is operated to assume at least the position 35 in which pressure fluid is supplied from feed conduit portion 15 through control conduit 34 to the control valve 37. Since no fluid is supplied through control conduit 26 to control valve 37, the pressure created by control conduit 34 causes movement of control valve member 39 to the position 43 in which the duct in valve member 39 connects the consumer conduit portions 17a and 17 so that the main pump 16 supplies fluid to the consumer apparatus 18 as long as the filling pressure in feed conduit portion 15 is sufficiently high to operate the pressure limiting valve 29.

If a required filling pressure is not reached in feed conduit portion 15, or drops, the spring 31 urges valve member 32 to position 33 in which no fluid is supplied to control conduit 34 so that spring 38 moves control valve member 39 of control valve 37 to the control position shown in FIG. 1 in which the fluid is idly circulated by main pump 16 through return conduit 42.

A pressure differential occurs upstream and downstream of filter 14 which acts by fluid in channels 19' and 19" on valve member 24 of the pressure responsive valve 22 against the force of spring 23. The force of spring 23 is adjusted to a predetermined pressure corresponding to the permissible pressure differential at filter 14. As long as filter 14 is not very dirty, the pressure drop at filter 14 is at the permissible pressure differential, and the valve member 24 of pressure responsive valve 22 remains in the normal inoperative position 25.

In the event that dirt deposited in filter 14 increases the flow resistance of filter 14, the pressure drop at filter 14 causes a pressure differential which is sufficient to overcome the force of spring 23 so that valve member 24 moves to the actuated position 27 in which ducts in valve member 24 connect feed conduit portion 13 with the discharge reservoir 21, and also with the control conduit 26 so that in the same pressure fluid from feed pump 12 flows to control valve 37, acting on control valve member 39 to move the same to the illustrated position in which the fluid pumped by main pump 16 idly circulates in return conduit 42. The control valve 37 is constructed as a three-way valve so that, except of leakage flow through control valve 37, no fluid is pumped through consumer conduit portion 17 to consumer apparatus 18. In an extreme case, only so much fluid needs to flow through filter 14 that the leakage losses of the main pump 16 are covered.

An increased pressure differential, with the consequent termination of discharge from main pump 16 through consumer conduit portion 17, may also be due to a cold condition of a viscous liquid pumped through feed conduit 13,15 by feed pump 12. In this event, the flow of the liquid through the ducts of valve member 24 in the position 27 has a throttling effect by which the fluid is heated, so that the apparatus becomes operative. Shifting of valve member 24 of pressure responsive valve 22 while the pumped fluid is in sufficiently warm condition, is an indication that the filter operation is faulty, and that the filter 14 must be exchanged.

The embodiment 11 of FIG. 1 assures that only the filtered fluid enters the main pump 16. Since pressure responsive valve 22 is controlled by the pressure differential at filter 14, filter 14 is protected from an excessively high pressure differential. The filling pressure set by the pressure limiting valve 29, can be selected independently of the pressure differential required for shifting pressure responsive valve 22. As long as the filling pressure is not reached, it is not possible to operate the main pump 16 to pump at full pressure.

The embodiment of FIG. 2 is identical with the embodiment of FIG. 1 as far as the elements on the left side of the chain line I--I are concerned, but FIG. 2 illustrates a modification of the parts shown on the right side of the line I--I. The first control conduit 26, the second control conduit 34, and the feed conduit portion 15 are shown to cross the line I--I.

The embodiment 50 shown in FIG. 2 has a variable output main pump 51 controlled by regulating means 52. The output of main pump 51 discharges through consumer conduit 17' to consumer apparatus 18. The output of main pump 51 can be varied manually by the manual linkage 53 which has an arresting recess schematically shown at 54 cooperating with an arresting member 55 operated by a piston and cylinder means 56. The chamber 58 on one side of the piston is connected with control conduit 26, which also extends to the regulating means 52, and chamber 57, through which the piston rod passes to arresting member 55, is connected with the second control conduit 34. A spring 55a acts on arresting member 55 in the same direction as fluid in chamber 58.

The embodiment of FIG. 2 operates as described with regard to the embodiment of FIG. 1, as far as the parts on the left side of the line I--I are concerned. When the pressure responsive valve 22 moves to an actuated position due to the high pressure differential at the filter 14, valve member 24 assumes the position 27 so that the feed pump 12 pumps pressure fluid through feed conduit portion 13, conduit 19, valve member 24 into the first control conduit 26 so that the fluid in the regulating means 52 operates the same to set main pump 51 to minimum output flow. Manual means 53 are operated, and due to the pressure from control conduit 26 in chamber 58, arresting member 55 moves into arresting recess 54 and locks the regulating means of main pump 51 in the position of minimum output flow. When the required filling pressure is again obtained in feed conduit portion 15, pressure limiting valve 29 responds so that in the position 35 of pressure limiting valve 29, pressure fluid flow through the second control conduit 34 into chamber 56 so that arresting member 55 is withdrawn.

When the output of main pump 51 is reduced to a minimum, no unfiltered fluid is supplied to the consumer apparatus. At the same time, fluid pumped by feed pump 12 into discharge conduit 19, is discharged into the reservoir 21, so that the amount of fluid flowing through filter 14 is substantially reduced.

The third embodiment 60 shown in FIG. 3 has a feed pump 61 which pumps fluid through a feed conduit portion 62, a filter 63, and another feed conduit portion 64, into the main pump 65 which is a constant output pump discharging into a consumer conduit 66 fluid toward consumer apparatus 67. The feed conduit portion 62 upstream of filter 63 is connected by a pressure limiting valve 68 to a discharge outlet opening into a reservoir 69 from which feed pump 61 pumps fluid. The pressure limiting valve 68 has a normal closed position, and is held in the same by a spring 68a.

Consumer conduit 66 is connected by a bypass conduit 71 with a pressure responsive control valve 72 which has a casing with ports for the bypass conduit 71, and other ports for control conduits 62',62" which are connected with feed conduit 62,64 downstream and upstream of filter 63, respectively, so that the pressure differential of filter 63 acts on the valve member 74, schematically shown, in addition to the spring 73. In the illustrated position, no fluid can flow through bypass conduit 71 into the feed conduit portion 64, but when valve 72 is shifted by an increased pressure differential caused by faulty condition of filter 63, a duct, schematically shown as an arrow, connects the interrupted portions of bypass conduit 71 so that the fluid pumped by main pump 65 flows through conduits 71 and 64 from the outlet of the main pump 65 to an inlet. A check valve 75 is provided in the feed conduit portion 64 downstream of the bypass conduit 71.

The operation of the embodiment 60 shown in FIG. 3 corresponds substantially to the operation of the embodiment of FIG. 1, and the pressure differential occurring at the filter 63 is used for controlling the fluid flowing through filter 63 to the constant output pump 65. Control valve 72 shunts pump 65 when the permissible pressure differential at filter 63 is exceeded, and the pressure responsive control valve 72 responds and shifts valve member 74 to the position in which main pump 65 is shunted by conduit 71,64.

The pressure limiting valve 68 determines the filling pressure for the main pump 65. In order to prevent damage to filter 63, the pressure differential to which pressure responsive control valve 72 responds, is selected in accordance with the permissible pressure drop at filter 63. Check valve 75 prevents that pressure surges from consumer apparatus 18 reach and affect filter 63. The function of the arrangement is assured, as long as, at the greatest permissible pressure differential, the amount of fluid flowing through filter 63 is greater than the leakage discharge of the main pump 65.

In the embodiment 80 shown in FIG. 4, a feed pump 81 pumps through a feed conduit portion 82, a filter 83, and a second feed conduit portion 84, fluid to the main pump 85 which discharges fluid through a consumer conduit 86 to consumer apparatus 87. A pressure limiting valve 88 has a discharge outlet 89 into a reservoir 103 from which feed pump 81 and main pump 85 may suck fluid. Pumps 81 and 85 are connected for rotation and driven by prime mover, not shown.

The main pump 85 is provided with regulating means by which the amount of fluid discharged through the outlet can be regulated under the control of a cylinder and piston motor 90. The differential piston 92 divides the cylinder into a piston rod chamber 93 and a piston chamber 94. A manually operated member 91 is connected with piston 92 and can be manually placed in a position in which the volume of chamber 93 is a minimum. Chamber 93 is connected by a conduit 95 with consumer conduit 86 and with the outlet of main pump 85, while chamber 94 is connected by conduit 96 with a pressure responsive valve 97 whose casing ends are connected by channels 101 and 100 with the feed conduit portions 82 and 84 upstream and downstream of filter 83, respectively. A spring 98 in the valve casing urges valve member 99 in the same direction as the pressure fluid of channel 100. Valve member 99 of the pressure responsive valve 97 has a normal position in which the conduit 96, and thereby chamber 94, is disconnected from a discharge conduit 102 which opens into a reservoir 103. In the actuated position of valve member 99, conduit 96 is connected with discharge conduit 102, so that fluid is discharged from cylinder chamber 94.

The operation of the embodiment 80 shown in FIG. 4 corresponds substantially to the operation of the embodiment 50 of FIG. 2, since the pressure drop at filter 83 is used for adjusting the regulating means 90 of the variable main pump 85.

As long as the pressure drop at filter 83 does not exeed a certain permissible value, feed pump 81 pumps fluid through filter 83 and feed conduit 82,84 into the inlet of main pump 85 which discharges into the consumer conduit 86. Pressure limiting valve 88 determines the filling pressure in feed conduit portion 82. The pressure in consumer conduit 86 acts also through conduit 95 in chamber 93, while chamber 94 and conduit 96 are separated from discharge outlet conduit 102 by pressure responsive valve 97.

Main pump 85 can be regulated by the regulating means 90, and when the manual member 91 moves piston 92 to a position reducing chamber 93 to a minimum by moving the piston rod as far out of the cylinder as possible, main pump 85 operates at the maximum output flow. If in this condition of main pump 85 and the regulating means 90, the pressure drop at filter 83 reaches a predetermined value due to high viscosity of the fluid, or due to clogging of filter 83, the pressure responsive valve 97 responds and valve member 99 is shifted, connects conduit 96 with conduit 102, and relieves chamber 94 of the regulating means 90 so that fluid flows out of chamber 94, and is discharged through conduit 96 and 102.

Fluid flowing through conduit 95 into chamber 93 acts on differential piston 92 so that main pump 85 is adjusted and set to a smaller output flow. The amount of fluid flowing through filter 83 is correspondingly reduced, since main pump 85 is mechanically coupled with feed pump 85 for rotation. The excess fluid pumped by feed pump 81 flows through the pressure limiting valve 88 into the discharge conduit 89 which opens into reservoir 103.

When the pressure drops at filter 83 is again reduced to the permissible value, pressure responsive valve 97 interrupts the connection between conduits 96 and 102 so that the normal operation can take place.

In the embodiment 80 of FIG. 4, the main pump 85 can be regulated only in a negative direction from maximim output to a zero position at a minimum output. The arrangement could be modified by providing a regulation in the positive direction, which would require instead of the return discharge conduit 102 to reservoir 103, a conduit connecting the pressure responsive valve 97 with the consumer conduit 86. In such an arrangement, the differential piston 92 would effect a return from a positive range of adjustments.

The hydraulic servo motors 56,90 shown for controlling the regulating means of the main pump in the embodiments of FIGS. 2 and 4 could be replaced by other regulating means, in which, for example, spring means are provided for returning the servo motor to a neutral position.

High pressure or low pressure may be used for the operation of the hydraulic regulating means for the variable main pumps, and the pressure fluid may come from a consumer system, or from an independent source of pressure fluid. The embodiments of FIGS. 1 and 3 in which main pumps of constant output volume are used, can be modified so that the main pumps are partly or completely shunted.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of arrangements for pumping filtered fluid differing from the types described above.

While the invention has been illustrated and described as embodied in an arrangement having pressure responsive control means responding to an excessive pressure drop at a filter for controlling the flow of a fluid from a feed pump through the filter to a main pump supplying consumer apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

Claims

We claim:

1. Arrangement for pumping a filtered fluid, comprising

a feed pump; main pump means including a main pump, and a consumer conduit through which said main pump discharges;

feed conduit means connecting said feed pump with said main pump so that only fluid pumped by said feed pump into said feed conduit means flows into said main pump;

filter means in said feed conduit means having a working condition causing a normal pressure differential in said feed conduit means, said filter means being disposed across the flow cross section of said feed conduit means so that all the fluid flowing in said feed conduit means to said main pump means flows through said filter means, and no fluid in unfiltered condition bypasses said filter means and flows into said main pump;

pressure responsive means connected with said feed conduit means upstream and downstream of said filter means and being in a normal inoperative position when said normal pressure differential indicates said working condition of said filter means, said pressure responsive means moving to an actuated position in response to a predetermined pressure differential different from said normal pressure differential and indicating a faulty filtering action of said filter means;

and control means for said main pump means operated by said pressure responsive means in said actuated position to terminate discharge from said main pump into said consumer conduit.

2. Arrangement as claimed in claim 1 wherein said main pump discharges a constant amount of fluid; wherein said control means include a control valve means having an operative position connecting said main pump with said consumer conduit, and a control position in which said main pump idles; and wherein said pressure responsive means include a pressure responsive valve responding to said predetermined pressure differential to move to said actuated position, and connecting in said actuated position said feed conduit between said feed pump and said filter means with said control valve means for moving the same from said normal position to said control position.

3. Arrangement as claimed in claim 1 wherein said control means include hydraulic regulating means for said main pump; and wherein said pressure responsive means include a pressure responsive valve responding to said predetermined pressure differential to move to said actuated position, and connecting in said actuated position said feed conduit between said feed pump and said filter means with said hydraulic regulating means so that fluid flowing from said feed pump to said hydraulic regulating means operates the latter to set said main pump to pump a minimum amount of fluid.

4. Arrangement as claimed in claim 1 wherein said pressure responsive means include a pressure responsive valve including a movable valve member, and a spring biassing said valve member into said normal inoperative position; wherein said control means include a control conduit; wherein said valve in said actuated position connects said feed conduit and said control conduit, respectively; wherein said predetermined pressure differential overcomes the force of said spring and moves said valve member to said actuated position; and wherein said control means are hydraulic control means operated in said actuated position of said valve by fluid flowing from said feed pump through said valve and said control conduit.

5. Arrangement as claimed in claim 1 comprising a discharge conduit connected with said feed conduit downstream of said filter means; and a pressure limiting valve in said discharge conduit spring biassed to a first position closing said discharge conduit when the pressure in said feed conduit is low, and at least a second position for supplying fluid to said control means for holding the same in a normal position in which said main pump discharges through said consumer conduit fluid fed by said feed pump at a normal pressure.

6. Arrangement as claimed in claim 1 wherein said control means include a control valve means including a control valve member, a valve casing, and a spring biassing said control valve member to a first position closing said consumer conduit; comprising a return conduit connecting said valve casing with said feed conduit downstream of said filter means and being connected with said consumer conduit in said first position so that said main pump idles, said control valve member having a second working position closing said return conduit and opening said consumer conduit; first and second control conduits connected with said valve casing so that pressure in said first control conduit acts on said control valve member to move the same to said first position, and pressure in said second conduit acts on said control valve member to move to said second working position; wherein said pressure responsive means include a pressure responsive valve connecting in said actuated position said feed conduit between said feed pump and said filter means with said first control conduit so that at said predetermined pressure differential said control valve member closes said consumer conduit; and comprising a pressure limiting valve connected with said feed conduit downstream of said filter means and including a limit spring urging said pressure limiting valve to a closed position, said pressure limiting valve moving to an operative position connecting said feed conduit with said second control conduit when the pressure in said feed conduit overcomes the force of said limit spring so that said control valve member is moved to said second working position.

7. Arrangement as claimed in claim 6 wherein said pressure limiting valve in said closed and operative positions disconnects said feed conduit from a discharge outlet, and has a third position assumed at high pressure in said feed conduit for connecting said feed conduit with said discharge outlet and with said second control conduit.

8. Arrangement as claimed in claim 1 wherein said control means include hydraulic regulating means for said main pump; wherein said pressure responsive means include a pressure responsive valve responding to said predetermined pressure differential to move to said actuated position, and connecting in said actuated position said feed conduit between said feed pump and said filter means with said hydraulic regulating means so that fluid flowing from said feed pump to said hydraulic regulating means operates the latter to set said main pump to pump a minimum amount of fluid; and wherein said regulating means further include manually operated means, and hydraulic arresting means for arresting said manually operated means.

9. Arrangement as claimed in claim 8 comprising a pressure limiting valve connected with said feed conduit; wherein said hydraulic arresting means include a cylinder, and a piston forming in said cylinder first and second chambers; said first chamber being connected by said pressure responsive valve with said feed conduit upstream of said filter means, and said second chamber being connected by said pressure limiting valve with said feed conduit downstream of said filter means; and wherein said hydraulic arresting means further include an arresting member operated by said piston so that said manually operated means are arrested when high pressure fluid from said feed conduit is supplied to said first chamber, and are released by high pressure fluid supplied to said second chamber.

10. Arrangement as claimed in claim 1 wherein said pressure responsive means include a valve casing, two conduits connecting said valve casuing with said feed conduit upstream and downstream of said filter means, a valve member in said casing between said conduits so that the pressure differential caused by said filter means acts on said valve member, and a spring acting on said valve member and urging the same into said normal inoperative position, said predetermined pressure differential overcoming the force of said spring and urging said valve member to said actuated position; and wherein said control means include a bypass conduit means connecting the inlet and outlet of said main pump and having ports on said valve casing, and a duct means formed in said valve member and connecting said ports in said actuated position of said valve member so that fluid is pumped by said main pump through said bypass conduit and said duct means and discharge through said consumer conduit is terminated.

11. Arrangement as claimed in claim 10 wherein said control means include a check valve in said feed conduit downstream of said filter means and upstream of said bypass conduit for protecting said filter means.

12. Arrangement as claimed in claim 1 wherein said control means include hydraulic regulating means for said main pump; wherein said pressure responsive means include a pressure responsive valve responsive to said predetermined pressure differential to move out of said normal inoperative position to said actuated position, and connecting in said actuated position said feed conduit with said hydraulic regulating means to operate the latter to set said main pump to pump a reduced amount of fluid; wherein said pressure responsive valve in said normal inoperative position connects said feed conduit with a discharge outlet; and wherein said pressure responsive valve includes a spring urging the same to said normal inoperative position.

13. Arrangement as claimed in claim 12 wherein said regulating means include a cylinder, and a differential piston and piston rod in said cylinder forming in the same a piston chamber and a piston rod chamber; wherein said piston chamber is connected with said feed conduit in said actuated position of said pressure responsive valve, and with said discharge outlet in said normal inoperative position; and wherein said piston rod chamber is connected with said consumer conduit.

14. Arrangement as claimed in claim 13 wherein said regulating means include manually operated means for moving said piston and piston rod in said cylinder to a position in which said regulating means set said main pump to maximum output which is reduced by said regulating means when said predetermined pressure differential prevails at said filter means and fluid from said consumer conduit flows into said piston rod chamber while said piston chamber is connected with said discharge outlet.

15. Arrangement as claimed in claim 12 comprising a pressure limiting valve connected with said feed conduit between said feed pump and said filter means and having a discharge outlet for discharging fluid from said feed conduit when the pressure in the same exceeds a normal pressure.

16. Arrangement as claimed in claim 1 wherein said main pump has a constant output volume; and wherein said control means include a conduit connecting the inlet and outlet of said main pump, and a control valve in said conduit having a position connecting said inlet with said outlet for idle circulation.

17. Arrangement as claimed in claim 1 wherein said control means include regulating means for said main pump; and wherein said pressure responsive means in said actuated position operate said regulating means to reduce the output volume of said main pump.

18. Arrangement as claimed in claim 1 wherein said pressure responsive means include a valve having a discharge outlet closed in said normal inoperative position, and connecting said feed conduit upstream of said filter means with said discharge outlet in said actuated position so that the flow through said filter is reduced when said predetermined pressure differential indicates a faulty condition of said filter means.