Apparatus For Proportionally Dosing A Plurality Of Liquids

Abstract

A proportionating dosing device has two pairs of pistons, each pair being mounted on the respective ends of a common piston rod. The piston rods are parallel and are coupled for movement in opposite directions by a two-armed lever whose fulcrum may be shifted to vary the ratio of the arms and thereby of the respective strokes of the piston pairs. The two cylinders receiving the pistons of each pair are connected with a common intake nipple and a common discharge nipple and controlled by pneumatically actuated valves, the pneumatic valve actuating circuits including conduits blocked and opened by the moving piston rods in proper sequence. Because of the wide available ratio of liquid discharge rates, the apparatus is suitable for metering resin compositions and curing agents for the same to an injection molding machine.

Description

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for proportionally dosing a plurality of liquids, and particularly to an apparatus for dosing liquid ingredients of a synthetic resin composition.

Known devices employed heretofore for this purpose are difficult to operate, do not provide a precisely adjustable and constant ratio of the several liquids to be dosed, and are limited in the range of available ratios.

The object of the invention is the provision of apparatus for proportionally dosing a plurality of liquids which is reliable in its operation and is capable of being adjusted over a wide range of proportions of the dosed liquids, at least between 1:1 and 1:200, and even higher ratios are preferred.

SUMMARY OF THE INVENTION

The invention, in one of its more specific aspects, provides apparatus in which a housing defines four cylinders. Four pistons respectively received in the cylinders constitute a first and a second pair of cylinders, a piston rod connecting the pistons of each pair for simultaneous movement between respective terminal positions of the pistons in the respective cylinders. Each piston rod and the two pistons connected thereby constitute a piston assembly.

Each cylinder is provided with an intake opening and a discharge opening so positioned that one piston of each pair moves toward the openings of the associated cylinder while the other piston of the pair moves away from the openings provided for the cylinder receiving the other piston. A linkage couples the piston assemblies for moving the pistons of each pair a first distance in the associated cylinders when the pistons of the other pair move a second distance. Adjusting means operatively connected to the linkage permit the first distance moved by each pair when the pistons of the other pair move the second distance to be varied.

A control valve associated with each cylinder may be moved by a valve actuating device between a first position in which the valve opens the discharge opening and closes the intake opening and a second position in which it closes the discharge opening and opens the intake opening. The actuating device is operated by pressure fluid derived from a suitable source and supplied through a supply valve which is operatively connected to one of the piston rods for supplying pressure fluid from the source to the valve actuating device and for thereby moving the control valve between its positions in response to movement of the piston rod.

A source of a first liquid is connected by the associated control valves with the intake openings of the two cylinders respectively receiving the pistons of the first pair, and a source of a second liquid separated from the first source is connected by the associated control valves with the intake openings of the two cylinders receiving the pistons of the second pair.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a dosing device of the invention in elevational section on the line I--I in FIG. 2;

FIG. 2 is a top elevation of the device of FIG. 1 on a smaller scale;

FIG. 3 shows a cover plate of the device of FIG. 1 in front elevation;

FIG. 4 illustrates another cover plate of the device of FIG. 1 in rear elevation, the scale of FIGS. 3 and 4 being smaller than that of FIG. 2;

FIG. 5 illustrates a modified embodiment of the invention in a view corresponding to that of FIG. 1; and

FIG. 6 shows a bottom plate of the device of FIG. 5 in plan view.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, there is seen a heavy rectangular plate member 1 which provides a central housing for operating elements of a double-dosing device of the invention. These elements include two identical pistons 2, 3 attached coaxially to respective ends of a common piston rod 4. The rod 4 is formed with two circumferential grooves 5, 6 respectively adjacent the pistons 2, 3.

Two pistons 7, 8, smaller in diameter than the pistons 2, 3, are mounted in an analogous manner on a common piston rod 9. The overall length of the pistons 7, 8 and of the piston rod 9 is equal to the corresponding dimension of the pistons 2,3 and of the piston rod 4. Circumferential grooves 10, 11 in the piston rod 4 are axially spaced from each other as far as the grooves 5, 6.

The pistons 2, 3 and 7,8 and the respective associated piston rods 4, 9 are movably received in parallel bores of the housing 1 which are of stepped-cylindrical shape, the four pistons being received in enlarged cylinder portions 57, 58, 59, 60 respectively. Four parallel conduits 12, 13, 14, 15 in the housing 1 rectangularly intersect the two bores of the piston assemblies in the section plane of FIG. 1. The conduits 12, 13 have plugged top ends and are downwardly open to the atmosphere, and the conduits 14, 15 are plugged at their lower ends and upwardly open.

The conduits 12-15 are smaller in diameter than the piston rods 4, 9. Their transverse spacing is such that, in the position of FIG. 1, the conduits 12, 14 are aligned with the grooves 5, 6 while being interrupted by the piston rod 9, whereas the conduits 13, 15 are aligned with the grooves 10, 11 and are interrupted by the piston rod 4.

The tubular housings 16, 16' of two slide valves extend along the narrow upright edges of the housing 1 and outwardly bound the cylinder portions 57-60. The valve slide in the housing 16' includes two coaxial, cylindrical stems 17, 18 of equal diameter sealingly received in the bore of the housing 16' and formed with respective circumferential grooves 19, 20 and integrally connected by a coaxial, circular valve actuating disc 26 of greater diameter. The identical valve slide in the housing 16 has two stems 21, 22 formed with grooves 23, 24 and connected by a valve actuating disc 25. The bores of the housings 16,16' have enlarged, cylindrical chambers 27, 28 in which the discs 25, 26 are axially movable in a limited path.

Pins 33, 34 project radially in a horizontal direction from the respective axially central portions of the piston rods 4, 9 into a longitudinal slot 61 of a link 37 freely movable in a central cavity 35 of the housing which is traversed by the rods 4, 9. Another pin 36 movable in the slot 61 between the pins 33, 34 is attached to a partly hollow and internally threaded upright rod 38. The blind, threaded bore of the rod 38 receives a threaded spindle 62 axially secured, but rotatable in a cover 62' which closes the cavity 35 in an upward direction and attaches the rod 38 to the housing 1. A knurled knob 62" on the outer end of the spindle 62 permits the pin 36 to be shifted vertically in precisely reproducible small increments. The link 37 thus constitutes a two-armed lever fulcrumed on the pin 36. The length ratio of the lever arms may be varied from the illustrated 1:1 ratio over a wide range by turning the knob 62".

As will presently be explained in more detail, the liquid to be dosed is admitted to and discharged from the cylinder portions 57-60 through ducts open when aligned with the circumferential grooves 19, 20, 23, 24 in the valve stems 17, 18, 21, 22. The pairs of pistons 2, 3 and 7,8 are coupled by the link 37 and are reciprocated by the pressure of the admitted liquid. Each cylinder portion 57-60 is shifted from liquid admission to liquid discharge by movement of the associated disc 25, 26 and of the grooves in the stems attached to the discs. The discs are moved by compressed air admitted to and vented from the chambers 27,28, flow of the air being controlled in the conduits 12-15 by the piston rods 4,9 and their circumferential grooves 5,6,10, 11.

The system of ducts for liquid and compressed air is formed partly by bores in the central housing 1 and the valve housings 16, 16', and partly by grooves in cover plates 31, 32, all grooves being located at the interfaces of the cover plates and the housings and being transversely sealed when the cover plates are attached to opposite upright faces of the housings by screws and gaskets not specifically illustrated and conventional in themselves.

The plate 31, as best seen in FIGS. 2 and 3, has four grooves 51-54 in its contact face with the housing 1, and is provided with nipples 29, 30, 39, 40 respectively communicating with the four grooves. The grooves 51-54 are parallel to the axes of the two piston assemblies 2, 3, 4 and 7, 8, 9 in the assembled device. The nipples 29, 39 are normally connected to respective sources 90, 91 of liquid under pressure, as is shown in FIG. 2 only, and the nipples 30, 40 are connected to devices respectively consuming the two separately dosed liquids and discharged through the nipples 30,40.

The cover plate 32, shown in FIGS. 2 and 4, carries a nipple 71 normally connected to a compressed air line or a compressor and communicating with a short groove 72 in the contact face of the plate 32 and parallel to the axes of the piston assemblies. Another parallel groove 74 in the plate 35 is connected with the nipple 71 by a bore 73 in the body 1 shown in phantom view in FIG. 4 and not otherwise illustrated. Two grooves 75,76 in the contact face of the cover 32 have respective straight end portions parallel to the axes of the piston assemblies. The two end portions of each groove 75,76 are transversely offset from each other and connected, respectively, by a bore 75' in the body 1 and by an obliquely inclined central portion of the groove 76.

In FIG. 1, the plate 31 is obscured by the body 1, and the plate 32 is in the portion of the device cut away. The ducts seen in the cover 32 in FIG. 4 are indicated in phantom view in FIG. 1 to facilitate the understanding of the device and of its operation. Since the plate 32 is seen in rear view in FIG. 4, the pattern of ducts shown in the phantom view of FIG. 1 is a mirror image of the pattern in FIG. 4.

Compressed air received by the nipple 71 flows from the groove 72 through bores 41, 42 in the body 1 into the top ends of the conduits 12, 13. The latter is blocked by the piston rod 4, but air can flow through the conduit 12 and the groove 5 in the piston rod 4 to a bore 43 in the housing 1 which leads into the groove 75 of the cover plate 32. Escape of air from the open lower end of the conduit 12 is blocked by the piston rod 9. Air flows in the conduit 75 to the chamber 27 above the valve actuating disc 25 and into the chamber 28 below the disc 26, thereby holding the discs in the illustrated position. The portion of the chamber 27 below the disc 25 and the portion of the chamber 28 above the valve disc 26 are vented to the atmosphere through the conduit 76, bores 44, 48 in the body 1 and respective portions of the conduits 13, 14 which communicate with the atmosphere through grooves 6, 10 in the piston rods 4, 9.

Liquid admitted to the groove 53 in the cover plate 31 by the nipple 29 flows to bores 55, 55' in the valve housings 16, 16' respectively. The bore 55' is blocked by the stem 22, but the bore 55' communicates with the cylinder portion 60 through the groove 20 in the stem 18 and an intake bore 69 in the wall of the valve housing 16'. The pressure of the admitted liquid tends to move the piston 8 away from the illustrated position.

The cylinder portion 59 ahead of the piston 7 is connected to the groove 24 by a discharge bore 68 in the wall of the valve housing 16 and thence to the groove 54 and the discharge nipple 30 by a bore 56 in the valve housing 16. The discharge bore 56' in the valve housing 16' and the intake bore 55 in the valve housing 16, respectively communicating with the grooves 54,53 are blocked by the valve stems 18, 22. When liquid under pressure enters the cylinder portion 60, a corresponding amount of liquid is discharged under the same pressure and at the same rate from the cylinder portion 59 through the nipple 30.

The cylinder portions 57, 58 are connected with the nipples 39, 40 respectively in an analogous manner. Liquid admitted to the groove 52 by the intake nipple 39 is barred from entering the cylinder portion 58 by the valve stem 17 which separates intake bores 50' and 66 in the valve housing 16' in the illustrated position of the disc 26. Liquid is free to enter the cylinder portion 57 through intake bores 50, 64 in the valve housing 16, which are connected by the groove 23 in the valve stem 21, and tends to shift the piston assembly 2,3,4 toward the right, as viewed in FIG. 1. Liquid may be discharged from the cylinder portion 58 under the liquid pressure acting on the piston 2 through discharge bores 65,49' in the valve housing 16' which are connected by the groove 19 in the valve stem 17, the groove 51, and the nipple 40.

The valve 17, 26, 18 is held in the illustrated axial position in the housing 16' by the pressure of air admitted to the chamber 28 from the nipple 71 through the bore 73, the groove 74, a bore 46 connecting the groove 76 to the conduit 15, the groove 11 in the piston rod 9, and a bore 47 connecting the conduit 15 to the groove 75 having an orifice in the chamber 28 below the disc 26. The groove 75 is additionally supplied with air under pressure through the conduit 12 as described above. The importance of the dual air supply to the groove, and of the dual venting paths from the groove 76 through the conduits 13, 14 will presently become apparent. The portions of the chambers 27, 28 respectively below the disc 25 and above the disc 26 are vented to the atmosphere through the groove 76 as described above.

As mentioned above, the liquid entering the nipples 29, 39 under pressure tends to shift the piston assembly 2, 3, 4 toward the right and the piston assembly 7, 8, 9 toward the left, the two piston assemblies being coupled by the link or lever 37 for simultaneous movement at the same rate. The piston rods 4, 9 are moved until the groove 5 is aligned with the conduit 13, the groove 6 is aligned with the conduit 15, the groove 10 is aligned with the conduit 12, and the conduit 14 with the groove 11.

In the non-illustrated other terminal position of the piston assemblies, air enters the chambers 27, 28 through the groove 76 and is vented to the atmosphere through the groove 75. Air enters the groove 76 from the groove 72 through the bore 41, conduit 13, groove 5, and bore 44, as well as from the groove 74 through a bore 45, conduit 14, groove 11, and bore 48, the conduits 13, 14 being sealed from the atmosphere by the piston rods 9 and 4 respectively.

The resulting upward shift of the valve assembly 21, 22, 25 and the downward shift of the valve assembly 17, 18, 26 almost instantaneously reverses the flow of liquid to and from the cylinder portions 57 to 60 so that the piston 2 is moved toward the illustrated position as liquid is discharged from the cylinder portion 57 through bores 63, 49 and the connecting groove 23 into the groove 51 and out of the nipple 40, the necessary pressure being supplied by liquid entering the cylinder portion 58 from the nipple 39 and the groove 52 through intake bores 50', 66 in the valve housing 16' as the same are connected by the circumferential groove 19 in the valve stem 17. In an analogous manner, liquid is discharged from the cylinder portion 60 to the nipple 30 through bores 70, 56' in the valve housing 16', the circumferential groove 20 in the valve stem 18, and the groove 54 in the cover plate 31. Liquid is admitted to the cylinder portion 59 from the groove 53 through bores 55, 67 in the valve housing 16 and the connecting groove 24 in the valve stem 22 until the condition of FIG. 1 is restored, and a new operating cycle begins.

The device illustrated in FIGS. 1 to 4 thus discharges two practically continuous streams of liquid from the nipples 30, 40 at respective rates which maintain a fixed ratio as long as the knob 62" is not turned. In the illustrated centered position of the pin 36 in the slot 61, this ratio is determined uniquely by the cross sections of the pistons 2,3 and 7,8. The pistons of both pairs travel over the full, equal lengths of the respective cylinder portions.

When the pin 36 is shifted in the slot 61 by means of the knob 62", only the pistons pivotally connected to the longer arm of the lever 37 have a stroke limited by abutment of the pistons against radial end walls of the associated cylinder portions. The pair of pistons connected to the shorter arm of the lever 37 sweeps only a part of its associated cylinder portions, but the resulting stream of liquid is still practically continuous. Adequate control of air flow is maintained by the circumferential grooves in the piston rod which moves through its full stroke. If the width of the link 37 at right angles to the plane of FIG. 1 is suitably selected, the pin 36 on the bar 38 may be aligned axially with either pin 33,34 so that the rate of liquid discharge from either nipple 30, 40 may be reduced to zero, permitting the ratio of liquid discharge to be adjusted continuously between .infin. : 1 and 1 : .infin. regardless of changes in the viscosities or pressures in the liquids entering the nipples 29, 39.

The device illustrated in FIGS. 1 to 4 and described above has been used successfully for controlling the injection of two synthetic resin compositions into respective parts of the same mold cavity, for injecting the same resin composition into a complex mold cavity from two gates, and for injecting a resin composition and a curing agent for the same simultaneously at a fixed ratio through a common gate. Flow ratios of 1:200 and higher were achieved without difficulty.

If so desired, more than two pairs of pistons may be coupled by the lever 37, and the lever may be replaced by a plurality of levers hingedly connected by pins engaging slots, each lever being provided with an adjustable fulcrum in the manner illustrated, if it is desired to vary the amount of liquid discharged by each of two or more pairs of pistons while the discharge rate from one pair is held constant so that the discharge ratio between any two pairs of pistons may be varied independently of the ratios between the other pairs.

The apparatus described above and illustrated in FIGS. 1 to 4 relies on the supply pressure of the liquid entering the nipples 29, 39 for controlling the pressure of the liquid discharged from the nipples 30, 40. The compressed air entering the device through the nipple 71 operates the valves in the liquid circuits, and its pressure is irrelevant within obvious limits. FIGS. 5 and 6 show a modification of the first-described embodiment of the invention in which the pressure of the air is employed for raising the pressure of the liquid discharged beyond that of the liquid taken in.

The modified apparatus includes all features of the first-described embodiment as far as not explicitly stated otherwise hereinbelow and operates in the same manner. Analogous elements are referred to in FIGS. 1 and 5 by the same reference numerals to which primes or lower case letters were added in FIG. 5 to indicate modifications. The second embodiment of the invention has a central housing 1' and valve housings 16a, 16b respectively attached to the narrow upright sides of the housing 1'.

The major piston assembly 2', 3', 4' differs from the corresponding assembly in FIG. 1 by a third, double-acting piston 77 mounted on the piston rod 4', and the piston rod 9' of the minor piston assembly carries a double-acting piston 78. The pistons 77, 78 reciprocate in respective cylinder chambers 79,80 of the housing 1'. The cylinder portion 57' in which the piston 2' moves may be supplied with compressed air backing the piston 2' during the discharge stroke through a duct a in the housing 1'. The two compartments of the cylinder chamber 79 axially separated by the piston 77 may be supplied with compressed air through ducts c, d, and ducts b, e similarly supply the compartments of the cylinder chamber 80. A duct f may supply backing air to the cylinder portion 58' which encloses the piston 3'. The ducts a-f may each be switched from supplying air to the associated cavity to venting the cavity.

The necessary connecting air conduits are largely provided by grooves 86,87,88 in the contact face of a bottom plate 83 normally sealed to the underside of the housing 1'. The groove 86 is aligned in the mounted bottom plate 83 with conduits 14', 15' which differ from the afore-described conduits 14,15 by the absence of plugs in their bottom ends. As described above with reference to the conduits 14,15, the lower end portions of the conduits 14', 15' permanently communicate with the compressed air nipple 71 through the groove 74 in the cover plate 32, not itself shown in FIGS. 5 and 6. The groove 86 thus is permanently connected with the nipple 71 and communicates with bores 86', 86" in the valve housings 16a, 16b, only the orifices of the bores in the valve housing being seen in FIG. 5.

The valve stems 18', 22' which are the structural and functional equivalents of the afore-described stems 18, 22 carry respective stem extensions 84,85 having each a circumferential groove 89 and an axial groove 90 axially offset from the groove 89 toward the open bottom end of the bore in the associated valve housing. Bores 81, 82 in the housings 1', 16a, 16b connect the grooves 87, 88 with orifices in the respective bores of the valve housings 16a, 16b which are axially aligned with the grooves 90 and circumferentially offset in a common radial plane from the orifices of the bores 86', 86".

The valve assembly in the valve housing 16a is shown in its lowered position in which it admits liquid to the cylinder portion 57'. Its circumferential groove 89 connects the bore 86' and thereby the compressed-air nipple with the bore 82 and the groove 88 of the bottom plate 83. The raised valve assembly in the valve housing 16b blocks the bore 86" and vents the bore 81 and the connected groove 87 to the atmosphere through the axial groove 90 in the valve stem extension 85.

Compressed air transmitted from the nipple 71 to the groove 88 is thus fed to the compartment of the cylinder chamber 79 to the left of the piston 77 and to the compartment of the cylinder chamber 80 to the right of the piston 78, as shown in FIG. 5, through the duct e, and to the annular rear face of the piston 3' through the duct f. The annular portion of the cylinder chamber 57', the right compartment of the cylinder chamber 79, and the left compartment of the cylinder chamber 80 are vented to the atmosphere through the ducts a, b, and d respectively. The pressure of the air thus is added to that of the supplied liquid in urging the upper or major piston assembly toward the right while urging the minor or lower piston assembly toward the left. Liquid is thus discharged from the nipples 30,40 at a pressure higher than that at which it is supplied to the nipples 29, 39.

The afore-described pneumatic system which enhances the pressure of the discharged liquid communicates with the pressure fluid circuit for controlling the valves only through the open bottom ends of the conduits 14', 15'. If higher supplementary pressure is needed, the bottom ends of the conduits 14', 15' may be plugged in the manner shown in FIG. 1, and the groove 86 may be connected with any other desired source of fluid under pressure, such as the discharge conduit of a hydraulic pump to receive oil under high pressure or the like through a nipple, not illustrated, and identical with the nipples 29,30,39,40 shown in FIG. 2.

If so desired, the devices of FIGS. 1 and 5 may be arranged in series by connecting one of the output nipples of one device with one of the input nipples of the other device, the remaining three input nipples being connected to respective sources of liquids to be dosed. Such an arrangement discharges three streams of liquid in a precisely determined volumetric ratio, one stream being delivered at the supply pressure and the other two at a higher pressure. Other series connections of devices of the types respectively shown in FIGS. 1 and/or 5 will readily suggest themselves to those skilled in the art to produce as many streams of liquids at precisely determined dosage ratios and pressures as may be required for a specific application.

It should be understood, therefore, that the foregoing disclosure relates only to preferred embodiments of the invention, and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the appended claims.

Claims

What is claimed is:

1. An apparatus for proportionally dosing a plurality of liquids comprising, in combination:

a. housing means defining four cylinders;

b. four pistons respectively received in said cylinders, said pistons constituting a first pair and a second pair of pistons;

c. a piston rod connecting the pistons of each pair for simultaneous movement between respective terminal positions of said pistons in the respective cylinders, each piston rod and the pistons connected thereby constituting a piston assembly,

1. each cylinder being provided with an intake opening and a discharge opening,

2. one piston of each pair moving toward said openings of the associated cylinder while the other piston of said pair moves away from the openings provided for the cylinder receiving said other piston;

d. linkage means coupling said piston assemblies for moving the pistons of each pair a first distance in the associated cylinders when the pistons of the other pair move a second distance;

e. a control valve associated with each cylinder and movable between a first position in which the control valve opens said discharge opening and closes said intake opening, and a second position in which said control valve closes said discharge opening and opens said intake opening;

f. pressure-fluid operated valve actuating means for moving each control valve between said two positions thereof;

g. a source of pressure fluid;

h. supply valve means interposed between said source and said valve actuating means and operatively connected to one of said piston rods for supplying pressure fluid from said source to said valve actuating means and for thereby moving said control valve between said positions thereof in response to said movement of said one piston rod;

i. a source of a first liquid connected by the associated control valves with the intake openings of the two cylinders respectively receiving the pistons of said first pair; and

j. a source of a second liquid separated from said source of said first liquid and connected by the associated control valves with the intake openings of the two cylinders receiving the pistons of said second pair.

2. An apparatus as set forth in claim 1, further comprising adjusting means operatively connected to said linkage means for varying said first distance moved by the pistons of each pair when the pistons of the other pair move said second distance.

3. An apparatus as set forth in claim 1, wherein said piston rods are elongated in a common direction, the pistons of each pair are spaced from each other longitudinally of the associated piston rod, and said linkage means include a fulcrum mounted on said housing means and a lever member pivotally mounted on said fulcrum, respective portions of said lever member spaced from said fulcrum being hingedly connected to said piston rods.

4. An apparatus as set forth in claim 3, wherein said lever member has two arms extending from said fulcrum in opposite directions and hingedly connected to said piston rods respectively, and said adjusting means include means for varying the ratio of the effective lengths of said arms and for thereby varying the ratio of said first distance and of said second distance.

5. An apparatus as set forth in claim 3, wherein said lever member is elongated and formed with at least one longitudinally elongated slot, and each of said piston rods carries an engaging member movably received in said at least one slot for hingedly connecting said lever member to said piston rods.

6. An apparatus as set forth in claim 5, wherein said fulcrum includes a pin member movably received in said at least one slot, and said adjusting means include means for moving said pin member toward and away from one of said piston rods.

7. An apparatus as set forth in claim 1, wherein said piston rods are elongated in a common direction, and the pistons of each pair are spaced from each other longitudinally of the associated piston rod, the apparatus further comprising two valve housings elongated transversely of said common direction and spaced from each other in said common direction so as to receive said housing means therebetween, each valve housing movably receiving a valve assembly including two of said control valves, said valve actuating means including two valve actuating members respectively fastened in said valve housings to said two control valves and constituting respective elements of the valve assemblies, said two control valves of each valve assembly being associated with cylinders receiving respective pistons of said first and second pairs, each of said two control valves being in said first position thereof when the other control valve is in the second position of the same.

8. An apparatus as set forth in claim 1, wherein said supply valve means include a conduit transverse to said one piston rod, said one piston rod having a first portion of a cross section greater than the cross section of said conduit and a second portion of a cross section smaller than the cross section of said conduit, said piston rod intersecting said conduit and sealing the same when said first portion thereof engages said conduit while permitting flow through said conduit when said second portion engages said conduit.

9. An apparatus as set forth in claim 1, wherein the pistons of each pair have the same cross-section different from the cross section of the pistons of the other pair.

10. An apparatus as set forth in claim 1, wherein said housing means define a fifth cylinder, one of said piston rods carrying an additional piston received in said fifth cylinder for joint movement therein with the pistons of the pair connected by said one piston rod, and means for supplying a pressure fluid to said fifth cylinder and for thereby urging said one piston rod to move.