US2380973A

US2380973A - Control for fluid operated motors

Info

Publication number: US2380973A
Application number: US498139A
Authority: US
Inventors: Carl J Kopp
Original assignee: FED ELECTRIC Co Inc
Current assignee: FED ELECTRIC Co Inc; FEDERAL ELECTRIC COMPANY Inc
Priority date: 1943-08-11
Filing date: 1943-08-11
Publication date: 1945-08-07
Anticipated expiration: 1962-08-07

Description

. -Aug. 7, 1945. Y c. J. KOPP k CONTROL FOR FLUID OPERATED MOTORS Filed Aug. 11, 1943 4 Sheets-Sheet 1 J52 1/972 1 0 7": CarZJ/ZO Z 1 -c. J. KOPP CONTROL FOR FLUID OPERATED MOTORS 4 sheets sh'eet 2 Filed Aug. 11, 1945 0 0' 5 Zw z Z w f m %z 7 W- W i "Hg W w 0 a a aw/Ma Z/ A 7 57 9 0w 1 50 5 7 6 WM 4 i Q 7 V 3\ 6 a 7 a 5/ 5 a w 7 5 Z w 5\ 5- U F J n r 9 Z 4 m fig 6 Z Aug. 7 1945. Q J KOPP 2,380,973

CONTROL FOR FLUID OPERATED MOTORS F298. I Fig.9 '79 82 45 5 7Y9 g5 55 l 59 l w :2? 70 LL11 57415.? 841010672757 Aug. 7,1945. Q j KOPP I 2,380,973

CONTROL FOR FLUID OPERATED MOTORS Filed'Aug. 11, 1945 4 Sheets-Sheet 4 62 Zawergizyg/ & 7 42527 Z Eatented Aug 7 1945 CONTROL FOB Um OPERATED MOTORS Carl J. Kopp, Chicago, Ill., alsignor to Federal Electric Company, Inc., Chicago,- Ill., a corporation of New York Application Angustll, 1943, Serial No. 493,139

7 Claims. (CI. -91),

This invention relates to control apparatus for fluid operated pistons, adapted to be utilized for controlling movement and/or positioningot various members or mechanisms, such as for example the height of a platen of a press, or the bed of a, milling or boring machine. More particularly the present invention is directed to apparatus for simultaneously controlling the movement of a plurality of pistons which are connected for moving various elements, or machines.

It has long been a problem to properly control the simultaneous operation of a plurality of fluid actuated pistons when said pistons are utilized, as for example, for raising or lowering various elements or parts of a machine. The simultaneous operation of a plurality of pistons necessitates great care and skill, as well as the consumption of a substantial amount of time.

One of the objects oi the present invention is to provide a novel control for simultaneously operating a plurality of fluid operated pistons for maintaining substantially synchronized or balanced movement of the piston elements.

Another object is to provide a novel control of the character indicated wherein a main control valve is adapted to be actuated in direct response to the differential of the rates of movement of two interconnected pistons -fo'r proportionately varying the rate of flow of fluid to the pistons, and thereby automatically causing "substantially balanced or equalized movement of thepiston elements.

A further obiect'is to provide an improved control of the character indicated by virtue of which the rate of movement of a plurality oi interconnected pistons serves to automatically effect adjustments of a main control valve so vas to maintain substantially uniform, balanced movement of the piston elements.

Still another object is to provide 'a novel tw0-' directional fluid control valve for a fluid system comprising a pair of cooperating telescoping valve elements, each connected to' a separate rotatable shaft, and'wherein a small amount of relative rotation of one shaft with respect to the other instantly efl'ects adiustmentof the valve elements by virtue of which said shafts are caused to rotate in substantial synchronism with each other.

Other objects and advantages of this invention will be apparent from the following description, taken in connection with the accompanying drawings in which:

Fig. 1 is a schematic illustration of my novel control apparatus for a pair oi fluid operated pistons.

Fig. 2 is a vertical section through the control valve per se.

Fig. 3 is a section through the control valve, taken as indicated on line 3-8 of Fig. 2.

Fig. 4 is a section through the'control valve,

drawings.

The control apparatus herein disclosed may utilize fluid in the tom of gas or a liquid, and for purpose of illustration the present invention will hereinafter be described as being operated by liquid, such as oil.

In Fig. 1 of the drawings I have shown a pair of fluid operated motors, designated generally at it and ii, disposed in upright. position, each comprising a cylinder M; and a piston element ll, reciprocably movable within the cylinder id. The upper end of each piston rod It of the piston elements is rigidly attached to a vertically disposed toothed rack it, mounted for slidable guided vertical movement, on the outer wall of the cylinder i4. Meshed with each of said racks is a pinion ll. Bald pinions are rigidly mounted on the outer ends of a pair of axially aligned, rotatable shafts ill and 2', which are operably associated with a main control valve designated generally at ii.

The control valve ii is constructed so as to maintain substantially synchronized or rotation of the two shafts I! and II and by virtue of which the piston elements of the respective motors II and H are. caused to be raised or lowered in relatively synchronized relation to each other. It is'to be imderstood that the upper ends of the piston rods I! may be operably connected to the machine bed or other object to be moved or supported thereby. The control valve is a hydraulically balanced unit and is operable by hydraulic pressure without having to overcome any resistance caused by pressure within it. Such an arrangement is particularly important if the control valve were operated by means other than racks and pinions, such as a cable and'drum, a Selsyn motor, or other meanswhich might not be capable of transmitting large amounts 01' power.

=1 atic illustration of the control apparatus represented in Fig. l of the As shown in Fig. 1 of the drawings, the upper ends of the chambered portion of the cylinders ll are interconnected by a duct or conduit, formed-in two sections, as indicated at 2 and 25 which are joined to a conduit 26, connected to a conventional reversing valve indicated generally at 21. The lower ends of the chambers of the cylinders are connected by ducts or

conduits

29 and 30, for the respective pistons l and H, to the main control valve 2|. The main control valve is interconnected with the reversing valve by a duct or conduit indicated at 32. Oil is supplied to the system through the reversing valve 21, by a conduit 34. connected to a pump 35, driven by a motor 36, for supplying oil through means of a conduit 38, from a storage tank 39. The reversing valve 21 is also connected by conduit 40 to the storage tank 39, to provide a return duct for the oil from the system to the source of upply.

The main control valve 2| includes a body 45 formed with a cylindrical bore 46 in which there is forcibly fitted a plurality of rings designated at 41, 48, 49, 50,51 and 52 which are axially spaced apart by rings designated at 53, the internal diameter of which is substantially greater than the internal diameter of the other rings, so

a as to provide five annular chambers designated as 55, 58, 51, 58 and 59. Snugly fitted within the bore 01' the rings 41 to 52 inclusive is a pair of cooperating telescopic valve elements designated at 6| and 62. The valve element BI is in .the nature of a sleeve, formed as an integral part of the shaft 20, and telescoped within the sleeve 61 is the valve element 62, which is the terminal portion of the shaft 19. The valve.elements are maintained in position within the valve body by end plates 63, abutting against a shoulder formed at the rear end of the sleeve GI, and against a collar I9 fixed on the shaft IS. The valve element 62 is formed with a pair of diametrically opposite, longitudinally extending passageways 65, which are in the form of keyway slots, terminating in approximate alignment with the outer walls of the

end chambers

55 and 59.

The sleeve 8| is provided with four pair of axially spaced apart ports 01, It, so and 10, with the ports of each pair disposed in diametrically opposed relation to each other, as seen in Figs.

6, 8 and 9 inclusive of the drawings. When the shafts l9 and 20 are rotating in synchronized relation to each other, the ports 61 to 10 inclusive are in semi-registration with the respective passageways 85 of the valve element 62. The ports 81 to 10 inclusive are open to and disposed in registration respectively with the

annular chambers

59, 58, n and 5!.

The sleeve Cl is also provided with a pair of diametrically opposite transverse slots 12, located at substantially the center of the length thereof,

that the chamber 5|, which is in registration with theports so, is in open communication with a port 18, which is in one-way communication with a duct 19, connected to the conduit 29. A one-way ball check valve designated generally at 80 interconnects the port 18 and duct 19.

In Fig. 8 of the drawings it will be noted that the chamber 56, in registration with the ports 69, is in direct communication with a port ll, which in turn is connected to the duct 16, connected to conduit 30, with a one-way ball check valve, indicated generally at 82, interposed in the duct 8| so as to provide a one-way passage for the flow of oil in the system. In Fig. 9 of the draw-- ings the chamber 55, in registration with the ports 10, is in direct communication with a port H, which' in turn is connected to the duct 19, with a one-way ball check valve, indicated generally at 85, interposed to provide a one-way passage of flow of oil.

For convenience, and for a more clear understanding of this invention, it may be here mentioned that the valve structure indicated in Fig. 5, controls the flow of oil to .eifect lowering of the piston element of the motor H The valve structure represented in Fig. 9, serves as the control for the lowering of the piston element of the in registration with the annular chamber 51, so as to provide direct communication between the pas sages l5 and a main port 11 formed in the valve body, and to which is connected the conduit .32.

The valve body is provided with separate ports and ducts for communication with the respective chambers inregistration with the ports 61 to 10 inclusive. As may be seen in Fig. 5 of the drawings, the chamber 59, which is in registration with the valve port 01, opens into a port 15, which is in one-way communication with a duct- 10, the latter being connected to the conduit 30.

'Interposed between the ducts II and I. is a one-way ball check valve designated generally at 11.- In Fig. 6 or the drawings it will be noted motor. Ill, and the valve' arrangements represented in Figs. 6 and 8, respectivelv control the raising of the piston elements of the motors l0 and I The reversing ,valve indicated generally at 21 may be understood to be of the spring centered type and normally has ports thereof so disposed that oil is caused to flow from the conduit 34.

directly into the conduit 40 so as to 'form a closed fluid system. The reversing valve may be operated in any convenient manner, and as herein shown by a pair of solenoids and 9 I. It is to be .understood that these solenoids may be separately and selectively energized by suitable switch means, not shown, for adjusting the reversing valve to either of two main positions of adjustment. For example, it may be assumed that when the solenoid 90 is energized the ports of thereversing valve are so adjusted that oil is pumped through the conduit 34 into the conduit 32, through the main control valve 21, and through the conduits 28 and 30, to the lower ends of the cylinders H of said motors Iii and H, for raising the piston elements. In this position oi adjustment of the reversing valve, the conduit 20 is, then through a suitable port arrangement of the reversing valve, in direct communication with the exhaust conduit 40, so as to permitthe oil in the upper end of the cylinders, above the piston elements to be expelled. and returned to the storage reservoir is. When solenoid I0 is deenergized and the other solenoid II is energized, the reversing valve then assumes aposition of adjustment wherein oil is pr nped through the conduit 84 into the conduit 20, and thence into the respective conduits 24 and II, into the upper ends of the chambers of the cylinders H, for causing lowering of the pistons I 5 within their respective cylinders. To accommodate such lowering action the oil in the lower ends oi the chambers of the cylinders is caused to flow through the conduits 2e and 30 into the main control valve II, from whence it flows through the conduit 32, which will then be-in direct communication with the exhaust conduit ll, tor returningfthe oil to the reservoir 30. The control valve ii, at this time will tune-- tion to equalize the lowering of the pistons by controlling the exhaust oil from the cylinders.

It may be understood that if desired, suitable limit switches may be employed for controlling the maximum and minimum position of adjustment of the piston elements, which would correspond to the limits of movement of the members to be controlled by the pistons, such as the platen of 'a press, or the bed of a machine. Such limit switches could be connected in series with the

respective solenoids

90 and 9|, soxthat when the pistons arrived at their uppermost limit of adjustment, the actuated solenoid would be deenergized so as to permit the reversing valve 21, to again assume its normal spring centered position of adjustment, at which time oil will then be pumped from the conduit 34 directly into the exhaust conduit 40, for return to the reservoir 39, and a proper quantity of oil will be sealed in the system, so,as to support the pistons at such position of adjustment.

It is also to be understood that if desired the pump motor may be controlled by relay circuits, connected incircuit with the respective solenoids and limit switches, so that the motor 36 functions only when one of the solenoids is energized and the limit switches are closed.

Operation of control valve valve, reading from right to left, correspond to the sections disclosed respectively in Figs. 5 to 9 inclusive.

If it be assumed now that the reversing valve der of the motor In, and a. reduced. quantity of oil would be supplied to the lower end of the cylinder of motor II. By virtue of this arrangement the two motors are almost instantly brought into synchronized adjustment, or relationship, so that they constantly tend to move in equalized or balanced relation to each other.

When the piston elements of the respective motors in and H are caused to be lowered by the readjustment of the reversing valve 21, by actuation of solenoid 9|, as above described, the oil is supplied through the conduit 34, directly into the conduit 26, for feeding the oil through the

conduits

24 and 25, into the upper end of the cylinder chambers. The oil at the bottom of the chambers, below the piston elements, is then forced through the respective conduits 29 and 39 into the main control valve 2| and the oil from the conduit 29 passes through the ball check valve 85, through the duct 94 into the chamber 55, surrounding the ports 10 through which the oil then feeds into the passageways 65, and the oil from the conduit 30 feeds into the duct 16, and through the one-way check valve 11 and duct I5 into the chamber 59, surrounding the ports 61, and then discharges into the passageways 65. The oil is then discharged from the passageways through the slots 12, port 13 into conduit 32, for return through the reversing valve 21, to the storage supply tank 39.

In the event one of the piston elements tends to travel downwardly at a rate of speed, in excess of the other, it will result in relative rotation of the shafts I9 and 20 with respect to each other,

21 is adjusted by actuation of solenoid 99, so as to cause raising of the piston elements in their respective cylinders, the oil is supplied from'the conduit 94 directly to the conduit 32,.and enters the chamber 51 of the main control valve. Oil then flows into slots 12 of the sleeve valve element Bl, into passageways 65, in the inner valve element 62, from whence it flows through the ports 68 and 69 (see Figs. 6' and 8), into the

chambers

58 and 56, into the

respective ducts

19 and 8| which are in direct one-way communication with the

conduits

29 and 30 respectively,

so as to supply oil to the lower portion of the cylinders of the respective motors Ill and II. It will be noted that at this time oil cannot flow through the

ports

61 and 10 because of the one-,

way ball check valves" and 85. When the reversing valve is so adjusted the oil 'at the upper ends of cylinders I4 is permitted to return through the

conduits

24, 25, and through the conduit 26, to theexhaust conduit 40, for return to the'storage reservoir 39. If during the raising action of the two pistons one of the pistons tends to travel faster than the other, as for example the piston element in the motor II, this will cause the shaft 20 to rotate a slight amount relatively to the shaft l9. This, as ay be observed from Fig. 6 of the drawings, wo' to rotate, in countercloc direction, slightly in excess of the rate of rotation of the valve 'element 62, which would cause the ports 88 to increase their registration with the passageways 65, while at the same time it would cause the ports 69, as seen in Fig. 8 of the drawings, to decrease the extent of their registration with said passageways 95. Thus a greater proportion and by virtue of which adjustment of the

ports

61 and 10 with respect to the passageways 65 is effected in the same manner as above described in connection with the raising of the pistons, that is, the main control valve 2| becomes adjusted for proportionately increasing the flow of oil from the piston which is moving the slower of the two, while at the same time reducing the quantity of oil flowing from the other piston which is traveling at the higher rate of speed. During the lowering operation oil cannot flow through the

ports

68 and 69 because of the oneway

ball check valves

80 and 82.

It will be noted that full oil pressure is exerted I maybe so limited by the appended claims.

cause the sleeve z iil of the available oil supplied through the duct I claim as my invention: 1. In combination with a fluid operated motor comprising a cylinder and a piston element reciprocably movable in th cylinder, a controlv for the motor comprising a toothed rack, connectedto and movable with the piston element, a pinion meshed with and rotatable incident to such movement of the rack, a control valve comprising a body provided with a main port and spaced apartinlet and outlet ports, check valves in said inlet and outlet ports to permit passage of fluid in only one direction therethrough, two

I do not, therefore, wish to shafts, one of said shafts having a terminal portion extending into said valve body and constituting a valve element, said shaft portion being provided with an elongated passageway, a sleeve connected to the adjacent end of the other shaft and disposed in said body in surrounding relation to said shaft portion, said sleeve being provided with axially spaced apart inlet and outlet ports normally disposed in registration with said passageway and an opening to provide direct communication between said passageway and main port, said valve body having internal chambers to provide communication between said inlet and outlet ports of the sleeve and the,

corresponding inlet and outlet ports of the body, one of said shafts being rigidly connected to said pinion, a source of liquid supply, a pump connected to said supply, a reversing valve, duct means connecting the pump to the reversing valve, duct means connecting the reversing valve and main port of the control valve, duct means connecting the reversing valve to one end of said cylinder, duct means connecting the opposite end of the cylinder to the inlet and outlet ports of the valve body, and duct means connecting the reversing valve to the source of fluid supply, whereby the adjustment of the reversing valve to one position, during synchronized relationship of said shafts, causes fluid to enter one end of the cylinder to move the piston element and simultaneously causes the fluid at the opposite end of the cylinder to return to said source of fluid supply, and adjustment of the reversing valve to another position, during synchronized relationship of said shafts, causes fluid to enter said opposit end of the cylinder to move the piston in an opposite direction and causes the fluid at said one end of the cylinder to return to said source of fluid supply.

2. In combination with a fluid operated motor comprising a cylinder and a piston element reciprocably movable in the cylinder, 9, control for the motor comprising a toothed rack, connected to and movable with the piston element, a pinion meshed with and rotatable incident to such movement of the rack, a control valve comprising a body provided with a main port and spaced apart inlet and outlet ports, check valves in said inlet and outlet ports to permit passage of .fluid in only one direction therethrough, two oppositely extending axially aligned rotatable shafts, one of said shafts having a terminal por tion extending into said valve body and constituting a valve element, said shaft portion being provided with two circumferentially spaced apart longitudinally extendingpassageways, a sleeve connected to the adjacent end of the other shaft and disposed in said body in surrounding relation to said shaft portion, said sleeve being provided with dual sets of axially spaced apartinlet and outlet ports normally disposed in registration with said passageways and an opening to provide direct communication between said passageways and said main port, said valve body having; internal chambers providing communication between the dual sets of inlet and outlet ports of the sleeve and the corresponding inlet and outlet ports of the body, one of said shafts being rigidly connected to said pinion, a source of fluid supply, a pump connected to ,said supply, a reversing valve, duct means connecting the pump and reversing valve,

duct means connecting the reversing valve and oppositely extending axially aligned rotatable necting the'reversing valve to one end of said cylinder, duct means connecting the opposite end of the cylinder to the inlet and outlet ports of the valve body, and duct means connecting the reversing valve to the source of fluid supply, whereby the adiustment of the reversing valve to on position, during synchronized relationship of said shafts, causes fluid to enter one end of the cylinder to move the piston element and simultaneously causes the fluid at the opposite end of the cylinder to return to said source of fluid supply, and adjustment of the reversing valve to another position, during synchronized relationship of said shafts, causes fluid to enter said opposite end of the cylinder to move the piston in an opposite direction and causes the fluid at said one end of the cylinder to return to said source of fluid supply.

3. A two direction fluid control valve comprising a body provided with a main port and spaced apart inlet and outlet ports, check valves in said inlet and outlet ports to permit passage of fluid in only one direction therethrough, two oppositely extending axially aligned shafts, oneof said shafts having a terminal portion extending into said valve body and constituting a valve element, said shaft portion being provided with an elongated passageway, and a sleeve connected to the adjacent end of the other shaft and disposed in said body in surrounding relation to said shaft portion, said sleeve being provided with two sets of axially spaced apart inlet and outlet ports adapted to be disposed in substantially semiregistration with the passageway and a separate opening providing direct communication between said passageway and said main port, said valve body being provided with internal chambers providing communication between said inlet and outlet ports of,the sleeve and the corresponding inlet and outlet ports of the body, whereby a small amount of relative rotation of one shaft with respect to the other in one direction, during either direction of flow of the fluid, increases the effective registration of one set of inlet and outlet ports of the sleeve with the passageway and decreases the eflective registration of the other set of inlet and outlet ports of the sleeve with said passageway, and opposite relative rotation of said shafts, during either direction of flow of the fluid, decreases the effective registration of said one set of inlet and outlet ports of the sleeve with the passageway and increases the effective registration of said other set of inlet and outlet ports of the sleeve with said passageway. 4. A two direction fluid control valve comprising a body provided with a main port and spaced apart inlet and outlet ports, check valves in said inlet and outlet ports to permit passage of fluid in only one direction therethrough, two oppositely extending axially aligned shafts, one of said shafts having a terminal portion extending into said valve body and constituting a valve element, said shaft portion being provided with two circumferentially spaced apart longitudinally extending passageways, and a sleeve connected to the adjacent end of the other shaft and disposed in said body in surrounding relation to said shaft portion, said sleeve being provided with two sets of axially spaced apart inlet and outlet ports normally disposed respectively in substantially semi-registration with said passageways and a separate opening providing direct communication between said two passageways and said main port, said valve body being provided with internal chambers providing communication between the sets of inlet and outlet ports of the sleeve with the corresponding inlet and outlet ports of the body, whereby a small amount of relative rotation of one shaft with respect to the other in one direction, during either direction of flow of 5 the fluid, increases the effective registration of one set of inlet and outlet ports of the sleeve with said passageways and decreases the effective registration of the other set of inlet and outlet ports" of the sleeve with said passageways, and opposite relative rotation of said shafts, during either direction of flow of the fluid, decreases the effec-. tive registration of said one set of inlet and outlet ports of the sleeve with said passageways and increases the efiective registration of said other set of inlet and outlet ports of the sleeve with said passageways.

' 5. In combination, a pair of spaced apart hydraulically actuated motors each comprising a cylinder and a piston element reciprocably movable therein, two sets of liquid ducts connected 1 respectively to corresponding ends of the respective cylinders, an equalizing valve connected in one set of ducts, a reversing valve connected in the other set of ducts, a duct interconnecting the equalizing valve and reversing valve, means for supplying liquid, from a source of supply, under pressure to said reversing valve, a return duct connecting the reversing valve to the source of supply, said reversing valve being adapted in one position of adjustment to supply liquid under pressure to a corresponding end. of each of said cylinders and causing the liquid at the opposite ends to' return to the source of supply, and

adapted in another position of adjustment to supply liquid under pressure to said opposite ends of the cylinders and causing the liquid at said corresponding end of each cylinder to return to the source of supply, said equalizing valve comprising two relatively rotatable valve elements 40 for controlling the flow of liquid to and from corresponding ends of the cylinders and between said equalizing and reversing valves. and meanz operably connecting said valve elements to respective pistons, said elements being adjustable relatively to each other in response to the difierential of the rate of movement of said pistons for proportionally varying therate of flow of the equalizing valve .and reversing valve, means for 60 supplying liquid. from a source 01' supply, under pressure to said reversing valve, a return duct connecting the reversing valve to the source oi! supply, said reversing valve being adapted in one able therein, two sets ofliquid ducts connected position of adjustment to supply liquid under pressure to a corresponding end of each of said cylinders-and causing the liquid at the opposite ends to return to the source of" supply, and adapted in another position of adjustment to supply liquid under, pressure to said opposite ends of the cylinders and causing the liquid at said corresponding end of each cylinder to return to the source of supply, said equalizing valve comprising two relatively rotatable valve elements telescopedone within the other and provided with suitable ports for communicating with said one set of ducts and with. the said duct interconnecting the equalizing valve and reversing valve, and means operably connecting said valve elements to the respective pistons, said elements being adjustable relatively to each other in response to the differential of the rate of movement of said pistons for proportionally varying the rate of flow of the liquid to or from corresponding ends of said cylinders, whereby to cause substantially equalized movement of said pistons.

7. In combination, a pair of spaced apart hydraulically actuated motors each comprising a cylinder and a piston element reciprocably movable therein, two sets of liquid ducts connected respectively to corresponding ends of the respective cylinders, an equalizing valv'e connected in one set of ducts, a reversing valve connected in the other set of ducts, a duct interconnecting the equalizing valve and reversing valve, means for supplying liquid, from a source of supply, under pressure to said reversing valve, a return duct connecting the reversing valve to the source of supply, ,said reversing valve being adapted in one position of adjustmentto supply liquid under pressure to a corresponding end of each of said cylinders and causing the liquid at the opposite ends to return to the} source of supply, and

adapted in another position of adjustment to' supply liquid under pressure to said opposite ends of the cylinders and causing the liquid at said corresponding end of each cylinder to return to the source of supply, said equalizing valve comprising two relatively rotatable valve elements telescoped one within the other and providedv with suitable ports for communicating with said vone set of ducts and with the said duct interconnecting the equalizing valve and reversing valve. a toothed rack extending longitudinally of each cylinder and operably connected to said pistons for movement therewith, a pinion meshing with each rack, and a pair of axially aligned shafts connected at corresponding ends to said pinions, and their opposite, adjacent ends being fixedly connected to the respective :valve elements, whereby the difl'erential rate of movement or said pistons eflects relative rotative adiustment'oithe valve elements for proportionally varying the rate of flow of liquid to or from said corresponding ends or the cylinders to cause substantially equalized movement or said pistons.

' 'cruu. J. Kora