US3270507A - Hydraulic control system - Google Patents

Description

- Sept. 6, 196 J. MERCIER ETAL HYDRAULIC CONTROL SYSTEM Filed June 16, 1965 7 r---- l I BYaeeA/meo M62 C ATTORNEY United States Patent 3,270,507 HYDRAULIC CONTROL SYSTEM Jean Mercier and Bernard Mercier, 1185 Park Ave., New York, N.Y. Filed June 16, 1965, Ser. No. 464,397 7 Claims. (Cl. 60-51) This application is a continuation-impart of copending application Serial No. 360,996, filed April 20, 1964, now Patent No. 3,223,382, dated December '14, 1965.

This invention relates to the art of hydraulic control systems, more particularly of the type to effect remote control of the rudder shaft of a ship.

As conducive to an understanding of the invention it is noted that the rudder shaft of a ship, especially when the ship is large, requires considerable force for actuation thereof through an appreciable range of movement and with sufiicient rapidity to take care of emergencies when the course of the ship must be rapidly changed. Where such force is supplied by a high torque hydraulic motor operatively connected to the rudder shaft and which is energized by a power source having a motor driven pump which feeds the motor, due to the kinetic energy of the heavy moving rudder, even when the power source is turned off, the rudder continues its movement for an additional amount.

This additional movement, although not critical when the ship is on the high seas with ample room in which to maneuver can be extremely dangerous when the ship is in a confined area such as when it is in a harbor.

It is accordingly among the objects of the invention to provide a hydraulic control system which is relatively simple in construction and dependable in operation, and which will provide both rapid movement of the rudder shaft of a ship over an appreciable range and with a simple control operation will also provide step by step movement of the rudder with substantially no overshoot from the desired setting of the rudder with controllable variations in the rate at which such step by step movement can be effected and which will also permit manual operation of the rudder in the event that the motor driven power source thereof fails.

According to the invention, these objects are accomplished by the arrangement and combination of elements hereinafter described and more particularly recited in the claims.

In the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

FIG. 1 is a diagrammatic view of one embodiment of the invention,

FIG. 2 is a longitudinal sectional view of a control valve utilized in the embodiment of FIG. 1, and

FIG. 3 is a schematic diagrammatic view of another embodiment of the invention.

Referring now to the drawings, the hydraulic equipment shown in FIG. 1 is designed to control the rudder shaft 11 of a ship.

To this end, the shaft 11 has secured thereto hydraulic motors 12 and 13 which may be of the type put out by Houdaille Industries, Inc., of Buffalo, New York, under the trademark Hyd-Ro-Ac, the motor 13 having a greater torque output than motor 12 for example, in the order of say ten to one, the motors being retained in fixed position in any suitable manner.

The motor 12 has pressure ports 14 and 15 connected by lines 16 and 17 to theports 18 and 19 of a control valve 20. The control valve 20 comprises a cylinder 21 having two spaced pistons 22 and 23 therein, mounted on a piston rod 24 which extends axially through the cylinder 21 and through the opposed ends 25 thereof, suitable seals (not shown) being provided in such ends.

One of the protruding ends of the piston rod 24 is pivotally connected by a link 26 to a pivoted control lever 27 for manual operation of the control valve 20.

Movement of the control lever 27 provides two different connections for the ports of the valve 20; in the neutral position shown, the ports 18 and 19 of valve 20 are in communication with each other through the annu lar chamber provided between the two pistons and when the lever is moved either to the left or right, the port 19 will be connected to port 31 and the port 18 will be connected to port 32. The ports 31 and 32 are connected by lines 33, 34 to the ports 35, 36 of a telemotor 37 which has a steering wheel 8 associated therewith.

The telemotor is of conventional type and includes a volumetric pump and a fluid reservoir so that based on a given angular rotation of the steering wheel 38 a given output will be provided.

In the illustrative embodiment herein shown, the steering wheel is connected through a step-down gear mechanism to the pump so that 360 rotation of the steering wheel will be related to a volumetric fluid output of the pump that will provide sufiicient flow at the required pressure to effect rotation of the motor 12 to turn the rudder shaft 11, say 18.

As such telemotor construction including the gear mechanism and volumetric pump arewell known in the art they will not be further described.

The lines 33, 34 are also connected by lines 41, 42 to the control ports 43, 44 at the respective ends of a fourway hydraulic control valve 45.

The control valve as shown in FIG. 2, comprises a cylindrical casing 46 having plugs 47 at each end with axial passageways 49 to the outer ends of which the ports 43,44 are connected.

Positioned in the bore 51 of the control valve is a control valve member 52 which has four spaced pistons 53a, b, c, d mounted on an axial rod 54. The control valve has ports 55, 56, 57, 58, 52 and 60. The bore of valve 45 has an annular shoulder 61 adjacent each end on which is seated a washer 62, the inner diameter of the washer being less than the diameter of the central portion 63 of the bore 51. The washers are retained on the shoulders by tensed coil springs 65, 66 compressed between the washer and the end of the adjacent plug 47. The valve member 52 is of length substantially equal to the longitudinal distance between the shoulders 61 so that when no pressure is applied to either of the control ports 43, 44, the valve member will be in the neutral position shown in which the two central pistons 53b and 530 will close ports 55, 56 and the ports 57, 58; 59 and 60 will lead respectively into the annular spaces between the adjacent pistons 53a, 53b; 53b; 53c and 53c, 53d. The control port 55 is connected by line 71 to the port 72 of motor 13 and the control port 56 is connected by line 73 to the port 74 of motor 13. The ports 57 and 59 are connected together by line 75 and also by line 76 to the reservoir 77 of the pressure source S. The pressure source includes a conventional motor driven pump 78 connected by line 81 to ports 58, 60 of the valve 45.

In the operation of the equipment shown in FIGS. 1 and 2, assuming that the ship is on the high seas with ample space to navigate, the helmsman will set the lever 27 to the neutral position shown in FIG. 1 in which the ports 14 and 15 of motor 12 are short circuited and the ports 31, 32 of the valve 20 are blocked. As a result, the motor 12 will not be in circuit.

Prior to application of pressure to the control ports 43, 44, as previously described, the pistons 53b and 530 will close ports 55, 56 and the ports 57, 58 and 59, 60 will lead respectively into the annular spaces between the adjacent pistons 53a, 53b; 53b, 53c and 53c, 53d.

As a result, since the fluid pressure line 81 is connected to both ports 58, 61B and as shown in FIG. 2, the ports 59 and 6b are normally in connection since they both lead into the annular space between pistons 53c, 530., the fluid under pressure from source S will flow through line 76 to the reservoir 77. Hence the valve acts as an open center valve in neutral position and since no fluid can flow to either of the control ports 55, 56 they will be blocked.

To steer the ship, the helsman need merely turn the steering wheel 38 in direction to effect the desired movement of the rudder until the steering wheel can no longer be turned. It is to be noted that since the port 35, for example, of the telemotor, through which fluid will flow, is connected to port 43 of the valve 45, the amount of fluid that can enter such valve is determined by the volume of the chamber C defined between the port 43 and the piston 53a when the latter has moved to its bottommost position due to the fluid pressure applied to port 43.

Consequently, it is clear that only a slightly amount of fluid can flow into such chamber C based on its volumetric capacity and the helmsman would only have to rotate the steering wheel a small amount, illustratively say, 10 which would be related to the volume of such chamber C. When the chamber C has been charged with fluid it will be noted that there will be resistance provided by the compression of the coil spring 66 which, acting on the valve member 52, will provide a resilient force against the body of fluid in chamber C and in the line 41 leading to the telemotor 37. The spring when compressed, illustratively is designed to provide a force against the valve member 52 that will create a pressure of say 10 atomspheres on the body of fluid in the chamber C and line 41.

As a result of such action by the helmsman which effected downward movement of the valve member 52, the ports 56, 58 of valve member 45 will be connected; the port 59 will be blocked by piston 53c and the ports 55, 57 will be connected.

Thus, fluid under pressure from source S will flow through line 81, ports 58, 56, line 73 to port 74 of motor 13 to cause the shaft 11 thereof to rotate, return of fluid from the motor 13 being effected from port 72, line '71, ports 55, 57 of valve 45, line 76 to reservoir 77.

Although fluid under pressure is also applied to port '60, since port 59 has been closed, the fluid under pressure applied to port 60 will have no affect.

So long as the helmsman retains pressure on the steering wheel 38, the valve member 52 will remain in the position described and there will be continued flow of fluid under pressure from source S to the motor 13 to effect rotation of the rudder.

When the helmsman by viewing an indicator 82 driven in conventional manner through a suitable servo-system 83 from the rudder shaft 11, sees that the rudder has turned the desired amount, he need merely release pressure on the steering wheel which will stop further flow from port 35 into line 41 and port 43. As such servoindicator system is conventional and forms no part of this invention, it will not be further described.

As a result of the drop in pressure in chamber C, due to the force exerted by the compressed spring 66, the valve member 52 Will move upwardly until the upper piston 53a abuts against the upper washer 62, fluid in chamber C being discharged therefrom through line 43 into port 35 of the telemotor. Since, at this time both of the springs 65, 66 will now be restrained by the abutment of washers 62 against shoulders 61 and since no further fluid under pressure is forced through either of the ports 43, 44, the valve member 52 will remain in neutral position with ports 55, 56 blocked and with the fluid from pump 78 being returned to the reservoir 77 due to the open center arrangement of valve 45 in neutral position.

As a result, there will be no further flow of fluid under pressure to the motor 13 and the rudder shaft will stop rotating and be retained in the angular position reached at such time.

To turn the rudder to neutral position in which it will be longitudinally aligned with the ship, the helmsman need merely rotate the steering wheel in the opposite direction, say 10 and the action above described will repeat in reverse direction and when the indicator shows that the rudder is in neutral position the helmsman need merely release the steering Wheel which will automatically return to the neutral position due to the volume of fluid forced in reverse direction through the volumetric pump.

In the event, for some reason, that the motor driven pressure source S should fail, steering action can still be effected.

In such case, the helmsman need merely move the lever 27 of valve 20 to connect ports 31, 19 and 32, 18 so that the motor 12 is in circuit.

Thereupon, by rotating the steering wheel in the direction desired for desired movement of the rudder, say in the direction to force fluid under pressure through port 35 a quantity of oil under pressure will be forced into the motor 12 to provide the desired steering action although at a much slower rate than would be effected by the motor 13 due to the fact that its torque output is considerably greater than that of motor 12. The reason that the motor 12 is of smaller torque output is that insuflicient quantity of oil could be supplied to the motor in a short period of time for rapid movement of the rudder shaft unless the pump in the telemotor was of very large size which would require more power than could be manually supplied by a helmsman. Due to the fact that the pressure in line 33, for example, will rise, when the steering wheel 38 is rotated, to an amount above 10 atmospheres and as such pressure will be applied to port 43 of valve 45, the valve member 52 thereof will move downwardly.

Hence, as above described, ports 55 and 56 will be connected to ports 57, 58 respectively of valve 45 to provide a path for the fluid to flow out of motor 13 into the reservoir 77. In the absence of such a path, since the hydraulic circuits into and out of motor 13 would be blocked, the motor 13 could not rotate freely thereby restraining free rotation of motor 12.

The operation of the equipment as above described with valve 20 in neutral position though completely satisfactory and desirable when the ship has large areas in which to manuever, raises certain problems when the ship must maneuver in a small area such as in a harbor when it is being docked. Thus, it is to be noted that with valve 20 in neutral position, when the steering action is effected by a slight rotation, i.e., 10 of the steering wheel, with the motor 12 short circuited, when the helmsman sees on his indicator 82 that the rudder is reaching the desired position, he must release the steering wheel before the desired position is reached due to the fact that the kinetic energy developed by the moving rudder will continue to move the rudder slightly even after flow of fluid to the motor 13 has ceased. Consequently, if the helmsman releases the steering wheel at the exact desired position of the rudder, the rudder will overshoot which is extremely dangerous in confined areas. The equipment above described is universal in its application in that coarse steering is provided on the high seas and fine steering may be provided in confined spaces by merely moving the lever 27 of valve 20 to connect ports 19, 311 and 18, 32 so that the motor 12 is in circuit.

With the motor 12 in circuit the as follows:

When the helmsman rotates the steering wheel 38, fluid under pressure will flow through line 41, for example, to control port 43 of valve 45 and also through ports 31 and 19 of valve 20 to port 14 of motor 12, return for steering operation is said motor being from port thereof through ports 18 and 32 of valve to port 36 of the telemotor.

As previously described, due to the small volume of chamber C of valve 45, a slight rotation in the order of 10 of the steering wheel will move the valve member 52 of valve 45 to its lowermost position against the tension of coil spring 66 thereby connecting the pressure source S to port 74 of motor 13 so that said motor 13 will rotate the shaft 11 thereof and also cause the shaft of motor 12 to rotate in the same direction. Due to the rotation of motor 12, cavitation in lines 17 and 33 will cause the pressure in line 41 to drop whereupon the tensed spring 66 of valve 45 will move the valve member 52 thereof upwardly to closed position, thereby blocking further flow to the motor 13.

Thus, with initial 10 rotation of the steering wheel, the rudder would only be moved a very slight amount, say one-half degree. At this time, since the valve 45 is in closed position, the ports 72, '74 of motor 13 are blocked which would prevent rotation of the shaft 11. Continued rotation of the steering wheel, say, another 10, will again cause the valve 45 to be actuated to move the rudder shaft another one-half degree before drop in pressure in line 41 again closes valve 45.

It is apparent from the foregoing that since each 10 rotation of the steering wheel effects one-half degree rotation of the rudder shaft, by continuous rotation of the steering wheel incremental movements in slight steps of the rudder is effected. Consequently, as the helmsman is rotating the steering wheel slowly, there is a step by step movement of the rudder shaft by small incremental amounts of one-half degree with a lapse between each incremental movement required to permit the pressure in line 41 to build up sufficiently to overcome the force of the spring 66 so that the valve member can move to open position.

It is apparent therefore, that if the helmsman stops such slow rotation of the steering wheel at any time, there will be extremely small overshoot, i.e., only a fraction of the one-half degree step which provides extremely precise maneuverability for confined areas.

This is to be contrasted with the rapid movement of the rudder shaft 111 effected when the pressure is applied continuously rather than in steps which causes the motor 13 to rotate continuously, which rotation when transferred to the heavy rudder, causes the rudder to continue swing- The universality of the system is apparent from the fact that even with the system set up for step by step movement of the rudder, the speed or rate of the step movements can be increased by the helsman as desired by more rapid turning of the steering wheel. Thus, absolute control is possible in confined quarters, i.e., slow step by step movement of the rudder or step movements at a higher rate of speed at which, even though there may be some overshoot, it will still be extremely small and controllable.

In the embodiment shown in FIG. 1, the control valve 45 is hydraulically operated. However, it is within the scope of the invention to have the control valve mechanically operated as shown in the embodiment of FIG. 3.

Referring to FIG. 3 in which parts corresponding to those shown in FIGS. 1 and 2, have the same reference numerals primed, the motor 12 and 13' are secured to the shaft 11'. Thus, the motor 12' has two relatively movable elements comprising its rotor and the motor housing, one of which is secured to shaft 11' and the other to valve 45 as hereinafter described.

The motor 13' is retained in substantially fixed position by means of a bar 80 pivotally connected at one end as at 80a to the hull of the ship and at its other end as at 8011 to a block rigid with the motor 13.

The ports 72, 74 of motor 13' are connected by lines 71', 73 to control ports 55', 56 of control valve 45'. The valve 45' is identical to valve 45 of FIG. 2 except 6 that instead of having the ports 43, 44 through which fluid under pressure may be applied, piston rods 85, 86 extend respectively through the openings 87, 88 in the end plugs 47' of valve 45 and are connected to the associated piston 53'11, 53d.

The ports 57, 59' of valve 45' are both connected through line 75, 76 to reservoir 77' of power source S and the port 58' is connected through lines 81", 81 to the fluid pressure output from pump 78' of the power source S.

If desired, the power source S can include a pressure accumulator 79 connected to line 81 through valve 60a and in such a case, the port 60' should be closed by a valve 60b.

The piston rod 86 of valve 45 is pivotally connected as at 91 to a link 92, pivotally connected as at 93 to a block rigid with motor 12. The ports 14, 15' of motor 12 are connected by flexible lines 16', 17 to the ports 35', 36 of telemotor 37 in order to take of the slight oscillations of motor 12'.

In the operation of the system shown in FIG. 3, to steer the ship, if the valve 60a is open so that the accumulator will be in the system, the valve 60b must be closed to prevent discharge of the accumulator through port 59 to the reservoir 77. The helmsman will turn the steering wheel 38 of the telemotor 37 in direction to effect the desired movement of the rudder. Fluid under pressure is applied to say port 14 of motor 12 and returned from port 15' to the telemotor.

As a result, the motor 12' attempts to rotate the rudder shaft. Due to the fact that in neutral position the ports 55, 56 of valve 45 are blocked, the ports 72, 74 of motor 13' will also be blocked and hence the casing of motor 12 will rotate about shaft 11'. As a result, assuming such rotation is in a clockwise direction from the position shown in FIG. 3, the link 92 will pull on piston rod 86. Hence, the control valve member of valve 45' will move downwardly, the movement of such valve member in either direction being limited by stops S, S.

The operation of the system will then be identical to the operation of the system of FIG. 1. Thus, fluid under pressure will be applied from the power source S through connected ports 58, 56 of valve 45' to port 74- of motor 13 to be returned from port 72 of motor 13, ports 55', 57 to reservoir 77 As a result of the rotation of shaft 11' by motor 13 say in a counterclockwise direction, this will cause the casing of motor 12' to turn in the same direction thereby restoring the valve member of valve 45 to neutral position.

Clearly, a step by step movement of the rudder will be accomplished, the rate of movement to be determined by the speed of rotation of the steering wheel by the helmsman.

In the event the telemotor 37' should be disabled, manual operation may be accomplished by actuation of lever a.

Although the motor 12 is shown as a rotary motor, it is to be understood that a piston rack and pinion actuation of conventional type could be used in place of such motor.

As many changes could be made in the above systems and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. A hydraulic control system for effecting rotary movement of a shaft on each side of neutral position, comprising a hydraulic motor operatively connected to said shaft to rotate the latter, said motor having control ports, a valve having control ports connected to the control ports of said motor, said valve having a fluid pressure inlet port, and a return port, a source of fluid under pressure connected to said pressure inlet port, and adapted to provide a constant source of pressure thereto, a reservoir connected to said return port, said valve having a movable valve member, resilient means reacting against said valve member normally retaining the latter in neutral position to block flow of fluid from said first pressure source through said control ports of said valve to said first hydraulic motor and to connect said pressure inlet port and return port of said valve, a control valve having a pair of control ports and a pair of operating ports, said valve having valve means controlling said ports, said valve means having a neutral position in which said operating ports are connected and said control ports are blocked and an operating position in which said control ports are connected respectively to the operating ports, a second source of fluid under pressure adapted to supply fluid under pressure only when actuated, said second source having a pair of ports connected respectively to said control ports of said control valve, said second fluid source ports selectively defining a pressure port and a return port, a second hydraulic motor operatively connected to said shaft, said motor having a pair of ports connected respectively to the operating ports of said control valve, and means opeartively connecting the ports of said second source to said first valve, to effect movement of said valve member to operative position, upon actuation of said second source, thereby to connect said pressure inlet port and said return port to said control ports of said first valve and to said first hydraulic motor.

2. A hydraulic control system for effecting rotary movement of a shaft on each side of neutral position, comprising a hydraulic motor operatively connected to said shaft to rotate the latter, said motor having control ports, a valve having control ports connected to the control valve, and means operatively connecting the ports su-re inlet port, and a return port, a source of fluid under pressure connected to said pressure inlet port, and adapted to provide a constant source of pressure thereto, a reservoir connected to said return port, a second source of fluid under pressure adapted to supply fluid under pressure only when actuated, said valve having a movable valve member, resilient means reacting against said valve member normally retaining the latter in neutral position to block flow of fluid from said first pressure source through said control ports of said valve, a second hydraulic motor having control ports and having two relatively movable elements, one of said elements being connected to said shaft, the other of said elements being connected to the movable valve member, means operatively connecting said second source to said control ports of said second hydraulic motor, whereby upon actuation of said second motor by said second source, movement of said other element of said motor will cause corresponding movement of the valve member of said valve, thereby to connect said inlet and return ports of said valve to the control ports thereof to actuate said first hydraulic motor.

3. The combination set forth in claim 2 in which said first pressure source includes a pump, a line connected between said pump and said pressure inlet port, and a pressure accumulator connected to said line, a valve between said pressure accumulator and said line, said mov able valve member being normally retained by said resilient means in position to block flow of fluid from said first pressure source through said control ports of said valve and to connect said pressure inlet port and return port of said valve and normally closed valve means to restrain flow of fluid from said accumulator to said reservoir when said first valve means is in open position.

4. The combination set forth in claim 2 in which said valve comprises a cylindrical casing having a movable valve member therein, said valve member having four spaced pistons movable in unison, the spaces between adjacent pairs of pistons defining a central chamber and two end chambers, a pair of pressure inlet ports are provided leading into said central chamber and one of said end chambers and a pair of return ports are provided leading into said two end chambers, a line connecting said two return ports and a second line con necting said two pressure ports, said first pressure source includes a pump, an additional line connected between said pump and said second line, a pressure accumulator connected to said additional line, a Valve between said pressure accumulator and said additional line, said movable valve member being normally retained by said resilient means in position for closure of said control ports by two adjacent pistons, and to connect the pressure and return ports leading into the same end chamber, normally closed valve means between said second line and the pressure port leading into said end chamber to restrain flow of fluid from said accumulator to said reservoir when said first valve means is open.

5. The combination set forth in claim 2 in which a control lever is operatively connected to said movable valve member for manual action thereof.

6. The combination set forth in claim 2 in which the movement of said other element of said second motor upon actuation by said second source is in direction opposed to the direction of movement of said shaft when fluid under pressure is applied to said first motor by reason of the actuation of the valve member by said movement of the said other element of said second motor.

7. A hydraulic control system for effecting rotary move ment of a shaft on each side of neutral position, comprising a hydraulic motor operatively connected to said shaft to rotate the latter, said motor having control ports, a valve having control ports connected to the control ports of said motor, and a fluid pressure inlet port and a return port, a source of fluid under pressure connected to said pressure inlet port and adapted to provide a constant source of pressure thereto, a reservoir connected to said return port, a second source of fluid under pressure adapted to supply fluid under pressure only when actuated, said valve having a movable valve member, resilient means reacting against said valve member normally retaining the latter in neutral position to block flow of fluid from said first pressure source through said control ports of said valve, a second hydraulic motor having control ports and two relatively movable elements, one of said elements being connected to said shaft and the other of said elements being connected to the mova-ble valve member, means operatively connecting said second source to said control ports of said second hydraulic motor, whereby upon actuation of said second motor by said second source, movement of said other element of said second motor will cause corresponding movement of said valve member of said valve from neutral position to operative position thereby to open flow of fluid to the control ports of said first motor to effect rotation of said shaft in direction opposed to the direction of movement of said other element of said first motor.

EDGAR W. GEOGHEGAN, Primary Examiner,

Claims (1)

1. A HYDRAULIC CONTROL SYSTEM FOR EFFECTING ROTARY MOVEMENT OF A SHAFT ON EACH SIDE OF NEUTRAL POSITION, COMPRISING A HYDRAULIC MOTOR OPERATIVELY CONNECTED TO SAID SHAFT TO ROTATE THE LATTER, SAID MOTOR HAVING CONTROL PORTS, A VALVE HAVING CONTROL PORTS CONNECTED TO TEH CONTROL PORTS OF SAID MOTOR, SAID VALVE HAVING A FLUID PRESSURE INLET PORT, AND A RETURN PORT, A SOURCE OF FLUID UNDER PRESSURE CONNECTED TO SAID PRESSURE INLET PORT, AND ADAPTED TO PROVIDE A CONSTANT SOURCE OF PRESSURE THERETO, A RESERVOIR CONNECTED TO SAID RETURN PORT, SAID VALVE HAVING A MOVABLE VALVE MEMBERS, RESILIENT MEANS REACTING AGAINST SAID VALVE MEMBER NORMALLY RETAINING THE LATTER IN NEUTRAL POSITION TO BLOCK FLOW OF FLUID FROM SAID FIRST PRESSURE SOURCE THROUGH SAID CONTROL PORTS OF SAID VALVE TO SAID FIRST HYDRAULIC MOTOR AND TO CONNECT SAID PRESSURE INLET PORT AND RETURNG PORT OF SAID VALVE, A CONTROL VALVE HAVING A PAIR OF CONTROL PORTS AND A PAIR OF OPERATING PORTS, SAID VALVE HAVING VALVE MEANS CONTROLLING SAID PORTS, SAID VALVE MEANS HAVING A NEUTRAL POSITION IN WHICH SADID OPERATING PORTS ARE CONNECTED AND SAID CONTROL PORTS ARE BLOCKED AND AN OPERATING POSITION IN WHICH SAID CONTROL PORTS ARE CONNECTED RESPECTIVELY TO THE OPERATING PORTS, A

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