US3608435A

US3608435A - Pressure controlled directional system

Info

Publication number: US3608435A
Authority: US
Inventors: Raymond S Conabee; Melville E Lawrence
Original assignee: Parker Hannifin Corp
Current assignee: DYNA-QUIP INCORPORATED A CORP OF OH; RESOURCE GENERAL Corp A OH CORP
Priority date: 1969-06-30
Filing date: 1969-06-30
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28
Also published as: GB1313876A; DE2032070A1

Abstract

A PRESSURE CONTROLLED DIRECTIONAL SYSTEM FOR A HYDRAULIC PRESS MOTOR CHARACTERIZED IN THE PROVISION OF A MOTOR REVERSING VALVE ASSEMBLY INCLUDING TWO SUPPLY VALVES AND TWO RETURN VALVES WHICH ARE CLOSED WHEN PILOT PRESSURE IS CONDUCTED THERETO AND WHICH ARE OPENED BY FLUID PRESSURE WHEN PILOT PRESSURE IS VENTED THEREFROM, AND A FOURWAY PILOT VALVE WHICH SELECTIVELY CONDUCTS PILOT PRESSURE TO SAID VALVES AND VENTS PILOT PRESSURE THEREFROM THUS TO ACTUATE THE PRESS MOTOR IN OPPOSITE DIRECTIONS. THE PILOT VALVE IS CHARACTERIZED IN THAT IT HAS A NEUTRAL POSITION WHEREAT ALL OF SAID VALVES HAVE PILOT PRESSURE VENTED THEREFROM SO THAT THEY MAY OPEN TO CONDUCT SYSTEM PRESSURE TO THE RESERVOIR AND WHEREAT THE PILOT PRESSURE INLET PORT THEREOF IS BLOCKED SO THAT PILOT PRESSURE STANDS AT THE PILOT VALVE PREPARATORY TO CONDUCTION TO SELECTED SUPPLY

AND RETURN VALVES. THE SYSTEM HEREIN IS FURTHER CHARACTERACTERIZED IN THAT THE SUPPLY AND RETURN VALVES ARE SPRINGBIASED AGAINST THE DIRECTION OF FLOW OF FLUID THERETHROUGH AND IN THAT IT HAS A DUAL PUMP ARRANGEMENT TO PROVIDE FOR RAPID ACTUATION OF THE PRESS MOTOR IN EITHER DIRECTION BY THE CONJOINT FLOW OF FLUID FROM A HIGH PRESSURE-LOW VOLUME PUMP AND A LOW PRESSURE-HIGH VOLUME PUMP.

Description

R. s. CONABEE ErAL 3,608,435

PRESSURE CONTROLLED DIRECTIONAL SYSTEM Sept. 28, 1971 2 Sheets-Sheet 1 Filed June 30, 1969 47 RAPID TRAVEL INVENTORS RAYMOND 5. CON/785E MELV/LLE E. LAWRENCE ATTORNEYS Sept. 28, 1971 5, CQNABEE ETAL 3,608,435

PRESSURE CONTROLLED DIRECTIONAL SYSTEM Filed June '30, 1969 2 Sheets-Sheet 2 I as I l 90 I I I INVENTORS J RA YMO/VD s. CONABEE MELV/LLE E. LAWRENCE ATTORNEYS United Smtes Patent 3,608,435 PRESSURE CONTROLLED DIRECTIONAL SYSTEM Raymond S. Conabee, Prospect Heights, and Melville E. Lawrence, Arlington Heights, 11]., assignors to Parker-Hannifin Corporation, Cleveland, Ohio Filed June 30, 1969, Ser. No. 837,854 Int. Cl. F15b 11/08 US. Cl. 91454 12 Claims ABSTRACT OF THE DISCLOSURE A pressure controlled directional system for a hydraulic press motor characterized in the provision of a motor reversing valve assembly including two supply valves and two return valves which are closed when pilot pressure is conducted thereto and which are opened by fluid pressure when pilot pressure is vented therefrom, and a four- Way pilot valve which selectively conducts pilot pressure to said valves and vents pilot pressure therefrom thus to actuate the press motor in opposite directions. The pilot valve is characterized in that it has a neutral position whereat all of said valves have pilot pressure vented therefrom so that they may open to conduct system pressure to the reservoir and whereat the pilot pressure inlet port thereof is blocked so that pilot pressure stands at the pilot valve preparatory to conduction to selected supply and return valves. The system herein is further characteracterized in that the supply and return valves are springbiased against the direction of flow of fluid therethrough and in that it has a dual pump arrangement to provide for rapid actuation of the press motor in either direction by the conjoint flow of fluid from a high pressure-low volume pump and a low pressure-high volume pump.

BACKGROUND OF THE INVENTION In general, it is Well known in the art of hydraulic control of a fluid motor for a hydraulic press and the like to employ a directional control valve having an inlet port connected with a pump, a return port connected with a reservoir, and at least one motor port connected with said fluid motor, said valve being operative to selectively communicate said motor port with said inlet port or said return port. In the case of a press having a double acting fluid motor, the directional control valve is usually of the four-way open center type having a pair of motor ports alternately communicated with said inlet and return ports to effect reciprocation of the motor piston. In small hydraulic systems four-way valves of this type can be used up to rated flow capacity without objectionable shock, but in large high speed hydraulic systems conventional four way valves produce severe shocks when attempted to be used at rated flow capacity. Accordingly, in order to avoid such shock, such systems may have to be operated below the rated capacities of the four-Way valves with consequent increase in cycle time, and furthermore, with spool type four-way valves, it may be necessary to decrease spool velocities during motor reversals. Thus, the maintenance of desired cycle time without shock may necessitate the use of larger four-way valves of overrated capacity or the use of separate decompression systems.

SUMMARY OF THE INVENTION The present invention relates as indicated to a pressure controlled directional system and has as its principal object the provision of a hydraulic system for a hydraulic press and the like which enables high-speed operation without shock, despite the fact that the pressure operated valves employed in the system handle oil flow exceeding the rated capacities thereof.

Another object of this invention is to provide a pressure controlled directional system which employs pilot operated first and second valves and a pilot pressure control valve which alternately vents and pressurizes said valves so that pump pressure will open said first valve to conduct fluid to the motor while said second valve is held closed by pilot pressure and so that fluid displaced from the motor will open said second valve while said first valve is held closed by pilot pressure.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully decribed and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic piping diagram of a pressure controlled directional system for actuating the fluid motor of a double ended hydraulic press or the like;

FIGS. 2, 3 and 4 illustrate various modifications in a pressure controlled directional system according to the present invention; and

FIG. 5 is a schematic piping diagram of another pressure controlled directional system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The FIG. 1 system comprises a main pump 1 and a pilot pressure pump 2 respectively connected to the pressure inlet ports of a pair of

sequence valves

3A and 3B and to the pressure inlet port P of a pilot pressure control valve 4. The outlet ports of

said sequence valves

3A and 3B are connected to the respective ports A and B of a double acting fluid motor 5 and to the respective inlet ports of a pair of relief valves 6A and 68.

Each sequence valve 3A and 33 has a spring biased, pressure seated main valve member 7 to block flow of fluid when there is inlet pressure (via

orifices

8, 9, and passage 10) or pilot pressure (via pilot passages 11 and 10) in the chamber 12 behind said main valve member 7. When the chamber 12 is vented through the pilot passages 10 and 11, the resulting pressure drop in chamber 12 will permit inlet pressure to move the main valve member 7 to open position to conduct fluid under pressure to one end of the fluid motor 5 (end A in the case of sequence valve 3A and end B in the case of sequence valve 38). Each

sequence valve

3A and 3B also has therein a spring biased pilot valve 14 which, when the pilot passages 10 and 11 are vented is moved to close off the orifice 9 thus to prevent leakage of fluid once the main valve member 7 has been opened as aforesaid.

Each relief valve 6A nd 6R comprises a spring bias pressure seated main relief valve member 15 which blocks the flow of fluid to the tank Whenever there is system pressure (via orifices 16. 17, and assa e 1 8\ or pilot essure (via pilot passages 18 and 19) in the chamber 20 behind said main valve member 15. The pressure in the chamber 20 may be decreased by ventin the pilot D saaes 18 and 19 whereby fluid displaced from the motor acts on the main valve member 15 and moves it to open po ition to a low returning fluid to flow into the ta k. Each relief valve 6A and B has a spring biased pilot valve member 21 therein which opens the chamber 20 and the pilot passages 18 and 19 to the tank port should the system pressure exceed a predetermined maximum. The resulting pressure drop in chamber 20 permits such excess pressure to open the main valve member for relief therepast into the tank. After relief of excess pressure the pilot valve member 21 will be spring biased to closed position whereby the chamber will again be pressurized to cause seating of the main valve member 15.

The pilot pressure control valve 4 preferably comprises a four-way closed center solenoid operated valve having a pressure port P connected to the pilot pressure supply line 23 from pilot pump 2, a tank port T for connection with a tank, and outlet ports A and B' which are connected respectively to the pilot passages 19 and 11 of the relief valve 6A and sequence valve 3B and to the pilot passages 19 and 11 of the relief valve 6B and sequence valve 3A. In the neutral position of said valve 4 all of the pilot passages 19 and 11 are connected to the tank port T whereby the fluid delivered by the main pump 1 may open all of the main valve members 7 and 15, thus to conduct the fluid delivered by pump 1 to the tank.

When solenoid 24 of the valve 4 is energized, port P is connected to port A thus to pressurize the pilot passage 11 in the sequence valve 3B and the pilot passage 19 in the relief valve 6A thus to urge the main valve members 7 and 15 therein to seated position. The port B is connected to the port T thus to vent the pilot passage "11 in the sequence valve 3A and the pilot passage 19 in the relief valve 6B. In this way, fluid delivered by the main pump 1 unseats the main valve member 7 in the sequence valve 3A and flows into the port A of the motor 5 and since the main valve member 15 in the relief valve 6A and the main valve member 7 in sequence valve 3B are at this time seated by pilot pressure, all of the fluid delivered by the pump 1 is conducted into port A of the fluid motor. As the piston moves to the left the fluid displaced from port B opens the main valve member 15 in the relief valve 6B, thus to conduct the returning fluid to the tank. When solenoid 26 is energized, port P is connected to port B thus to pressurize the pilot passage 11 in sequence valve 3A thus to force the main valve member 7 therein to seated position blocking flow of fluid through said sequence valve 3A and the pilot passage 19 in the relief valve 6B is pressurized to hold the main valve member 15 therein in closed position blocking flow of fluid through said relief valve 6B. At the same time, the pilot passage 11 in the other sequence valve 3B and the pilot passage 19 in the other relief valve 6A are vented from port A to port T whereby the fluid delivered by the main pump 1 will open the main valve member 7 in the sequence valve 3B thus to conduct fluid under pressure into port B of the motor 5, the relief valve 6B at that time being blocked. The fluid displaced from the port A of the motor 5 is conducted to the tank via the relief valve 6A.

The pilot pressure delivered by pilot pump 2 is preferably equal to or greater than the system pressure, and when the valve 4 is in neutral position, the pilot pressure stands as a static pressure through the check valve 27, there being a sequence valve 28 upstream of the check valve 27 to conduct the pilot pump delivery to the tank whenever the pilot pressure is at a predetermined value equal to or greater than that of the system pressure. However, should the system pressure rise so as to exceed the pilot pressure as, for example, by resistance encountered by the piston 25 during movement, the check valve 29 opens so as to maintain system pressure in the pilot system. The pilot pump 2 continues to develop pilot pressure by flowing through the sequence valve 28 which is upstream of the then closed check valve 27. The maximum system pressure may be controlled by a relief valve 30 if the limit is to be less than the relief pressure of either of the relief valves 6A or 6B.

If the fluid motor 5 is of the differential displacement type with, say, end A as the head end, the relief valve 6A associated with the head end of the motor 5 may be of larger size than the other relief valve 6B to accommodate the greater return flow or instead of that, am

4 other relief valve 6A may be connected in parallel to the existing relief valve 6A to handle the greater return flow.

It has been found that in the present pressure controlled directional system the

valves

3A, 3B, 6A and 6B, may be used at ratings substantially above recommended maximum ratings without any shock. As a specific example, valves rated at gal/min. flow have been used in the system for high speed operation at gal/min. with completely shock free action.

It can be seen that if increased cycle time can be tolerrated, the port P of valve 4 may be plugged and the pilot pump 2 omitted because seating pressure in the

chambers

10 and 20 may be developed from system pressure through the

orifices

8 and 9 and 16 and 17.

In FIG. 2 the valve assembly comprising

sequence valves

3A and 3B, the relief valves 6A and 6B, the fourway valve 4 and the relief valve 30 are shown in the phantom rectangle 31. In the FIG. 2 system there is shown a vertically disposed motor 32 and herein a single pump 34 supplies both system pressure (solid line) and pilot pressure (dotted line). The system pressure is supplied through a sequence valve 35 which is opened when pressure is at desired value. When the fluid motor 32 is in vertical position, the moving weight must be kept from falling when the system is in neutral position and for that purpose a counterbalance valve 36 has been added. The counterbalance valve 36 remains closed to support the moving weights. If the piston 37 is to be moved downwardly, pressure in port A will cause increase in pressure in port B sufficient to open the counterbalance valve 36 whereupon the lower end B of the cylinder will be exhausted through the unblocked relief valve 6B. When the piston 37 is to be moved upwardly, flow into port B is through the check valve 38 which may be a part of the counterbalance valve 36. The FIG. 2 system may, if desired, include a pilot feedback valve 39 to control neutral drift together with pressure regulation at the sequence valve 35. The

check valves

27 and 29 as shown in FIG. 1 are not required in FIG. 2.

In FIG. 3 there is shown a pressure controlled directional system (utilizing a pump 34 and sequence valve 35 as in FIG. 2, for example) which is so arranged that when pressure and flow are directed to the cylinder port A, return flow at port B is blocked at the unloading valve 40 and must flow through the counterbalance valve 41 and check valve 42 to augment the pump delivery to port A. When the system pressure rises above the setting of the unloading valve 40 it opens the port B to the tank through the unblocked relief valve 6B.

FIG. 4 shows a pressure controlled system applied to a position shift differential system with a solenoid 45 when energized along with solenoid 24 being effective initially to direct pump delivery from a main low pressure pump 46 to the cylinder port A with the fluid returning from port B being valved through the counterbalance valve 36 and the valve 47 to augment the pump 46 delivery. At a predetermined point in the stroke of the piston 48 the solenoid 45 will be de-energized to return the port B discharge to the line 49 where it returns to the tank through the unblocked relief valve 6B. In this case a dual pump is employed including a high pressure low volume. pump 50 and a low pressure large volume pump 46 and the sequence valve 51 is placed in the high pressure delivery line so that the discharge of both

pumps

46 and 50 is available for rapid downward travel of the piston 48. The FIG. 4 circuit also employs the counterbalance valve 36 to support the load in neutral position of valve 4 when the solenoid 45 is de-energized. In this case, the low pressure large volume pump 46 would discharge through the check valve 52 and rapid travel of the piston 48 may be effected through both

pumps

46 and 50 when the sequence valve 3B is unblocked and when the valve solenoid 45 is de-energized with fluid flowing through the check valve 38 of the counterbalance valve 36. As aforesaid the sequence valve 51 is located to be actuated by the pressure in the high pressure, low volume discharge line of the pump 50. The reference numeral 53 denotes a relief valve for the low pressure high volume pump 46.

The FIG. system incorporates simplified pressurecontrolled valving for directional control of a fluid motor, the same valving with slight changes serving as counterbalance valves, pilot operated relief valves, pump loading and unloading valves, and ordinary check valves. By way of example, the FIG. 5 system may be used in a die-casting trim press wherein it is desired that the piston or ram 60 (together with the platen and trimming die carried thereby) move down at a desired rate until such time as a decreased feed at high pressure is required for the trimming operation. Thereafter it is desired to retract the ram 60 at maximum speed to repeat the cycle.

The FIG. 5 system comprises a dual pump 61-62 of which the high pressure-low volume pump 61 supplies pilot pressure through conduit '63 to the port P of a four-way closed center pilot valve 64 and of which the low pressure-high volume pump 62 supplies system pressure through check valve 65 and conduit 66 to the inlet ports of a pair of pressure-controlled

valves

67A and 67B. The outlet ports of said

valves

67A and 67B are connected by

conduits

68 and 69 to the respective ports A and B of the ram cylinder 70, and to the inlet ports of another pair of pressure-controlled valves 71A and 71B. The outlet ports of valves 71A and 71B are connected as shown to the tank.

Each

valve

67A, 67B, "71A, and 71B has a springbiased, pressure seated valve member 72 therein to block flow of fluid therethrough when there is pilot pressure (via passage 73) in the chamber 74 behind said valve member 72. When chamber 74 is vented through the pilot passage 73, fluid pressure will move the valve member 72 to permit flow from the'inlet port to the outlet port.

The pilot pressure control valve 64 has outlet ports A and B connected to pilot passages 73 of

valves

71A and 67B and of valves 67A and 71B respectively whereby when solenoid 75 is energized pilot pressure from port P to port A pressurizes the chambers 74 of

valves

71A and 67B (via the check valve portion of the choke-check valve 77) to hold the valve members 72 therein in seated position, and the chambers 74 of valves 67A and 71B are vented through ports B and T. Thus, pressure in conduit 66 opens valve 67A to conduct fluid pressure to port A of the ram cylinder 70, and return flow from port B (when connected directly to conduit 69) opens valve 71B. When solenoid 76 is energized, pilot pressure from port P to port B pressurizes the chambers 74 of valves 67A and 71B to hold them closed, and the chambers 74 of

valves

71A and 67B are vented (via the choke portion of the choke-check valve 77 through ports A and T. Thus, pressure in conduit 66 opens valve 67B to conduct fluid pressure to port B of the ram cylinder 70 via conduit 69 and check valve 78, and return flow from port A and conduit 68 opens valve 71A, the opening rate being under the control of the choke portion of valve 77 to avoid rapid decompression of the cylinder 70.

Adjacent the pump 62 is an unloading valve 80 controlled by solenoid pilot valve 81 so that when solenoid 82 is de-energized, the chamber 83 is vented through pilot passage 84 to open valve member 85 thus to unload pump 62. When solenoid 82 is energized, pilot pressure through valve 81 and pilot passage 84 pressurizes chamber 83 to hold valve member 85 in closed position for supply of system pressure through check valve 65 and conduit 6'6 to open the then vented

valve

67A or 67B. It is to be noted that the valve 80 and valve member 85 may be identical in construction to the

valves

67A, 67B, 71A, and 71B and the valve members 72 therein.

Adjacent the pump 61 is a pilot operated relief valve assembly comprising a pilot relief valve 86 which when open bleeds fluid through pilot passage 87 and chamber 88 of the valve 89 faster than fluid can be replenished through the orifice 90 in the pressure seated, springbiased valve member 91. Thus, the ram 60 may be raised or lowered by the conjoint discharge of both pumps 61 and 62. As evident, the valve 89 and valve member 91 may be the same as

valves

67A, 67B, 71A and 71B and the valve members 72 therein, except that valve member 91 has the orifice 90 therein.

The system supply conduit 6'6 also has a system relief valve assembly 88'-86' which is the same as the valve assembly 88-86 just described except that the pilot relief valve 86 will have a higher pressure relief setting than pilot relief valve 86.

To prevent downward drift of ram 60 under the influence of its own weight and the weights of the platen, die etc. thereon, there is provided a pilot operated relief valve 92 which is held in closed position so long as there is no flow of fluid through the check valve 93 and the pilot relief valve 94 from the chamber 95 which is in communication with port B via the orifice 96 in valve member 97. The pilot relief valve 94 will be set to open at a pressure which will support the ram load against downward drift. As evident, when the ram 60 is to be moved downwardly the pressure in port B of the cylinder 70 will increase so that pilot relief valve 94 will be opened to vent fluid faster from chamber 95 than it can be replenished through orifice 96 in valve member 97. In this way the valve 92 is opened to permit return flow.

When valve 92 is opened as aforesaid, the return flow from port B opens either unloading

valve

98 or 99 depending on the position of the solenoid operated pilot valve 100. When the solenoid 101 of the pilot valve is de-energized (FIG. 5 position of pilot valve 100) pilot pressure in chamber 102 of valve 98 via check valve 103, pilot valve 100, and pilot passage 104 holds the valve member 105 in closed position. At this time, return flow from port B moves the valve member 106 to open position because the chamber 107 is vented through pilot passage 108 and pilot valve 100 whereby return is conducted to the reservoir via conduit 69 and the open valve 71B.

When solenoid 101 is energized, pilot pressure in chamber 107 of valve 99 holds the valve member 106 in closed position while the chamber 102 of valve 98 is vented. Thus, return flow moves valve member 105 to open position for augmenting the flow of fluid in conduit 68 into port A of cylinder 70.

Assuming that the ram '60 is in raised position as shown and that

pilot valves

64, 81 and 100 are in the positions shown in FIG. 5, the pressure control valve members 74 will all be vented through the pilot valve 64 so that

valves

67A and 71A or valves 67B and 71B may open by flow of fluid from pump 61 through relief valve 89 to maintain pilot pressure in conduit 63; pump 62 is unloaded by opening of valve 80 by venting the chamber 83 through pilot valve 81; and valve 98 is held closed by pilot pressure in chamber 102. The ram 60 is, at this time, held in raised position by ram pressure in the chamber 95 of valve 92. 'However, to prevent ram drift as by leakage, oil is supplied to port B through the choke-check valve 109 from the pilot pressure conduit 63.

To initiate downward movement of ram 60,

solenoids

75, 82 and 101 are energized whereby, (a) chambers 74 of

valves

71A and 67B are pressurized to hold said valves closed and chambers 74 of valves 67A and 71B are vented; (b) chamber 83 of unloading valve 80 is pressurized to close said unloading valve 80; and (c)

chambers

107 and 102 of

valves

99 and 98 are respectively pressurized and vented. Rapid descent of the ram 60 is thus achieved by delivery of fluid from both pumps 61 and 62 to port A of cylinder 70 via conduit 66, open valve 67A, and conduit 68. In addition, return pressure in port B opens

valves

92 and 98 whereby return flow through

valves

92 and 98 augments the delivery of pumps 61 and 62 to port A.

As the ram 60 approaches the feed limit,

solenoids

82 and 101 are de-energized respectively (a) to permit opening of the unloading valve 80 and (b) to close the valve 98 and to open the valve 99 for continued return flow through conduit 69 and valve 71B. In a die casting trim press, the trim operation then occurs by flow of high pressure oil from pump 61 into port A via conduit 66, valve 67A and conduit 68.

To initiate rapid upward movement of ram 60, solenoid 75 is de-energized and

solenoids

76 and 82 are energized, respectively, (a) to vent the chambers 74' of

valves

67B and 71A for flow of system pressure to port B via conduit 66, valve 67B, conduit 69 and check valve 78 and for return flow from port A through conduit 68 and valve 71A; and (b) to close the unloading valve 80 so that pump 62 augments the delivery of pump 61. In a die casting trim press, initial slow pullout may be achieved by energizing solenoid 82 after solenoid 76 has been energized whereby only pump 61 will deliver fluid to port B during the time that solenoid 82 remains de-energized. When the solenoid 75 is de-energized at the end of the high pressure work stroke of the ram 60, the choke-check valve 77 avoids rapid decompression of the cylinder 70.

When the ram 60 reaches its upper position, the

solenoids

76 and 82 are de-energized whereby the

pilot valves

64 and 81 return to the neutral positions as shown in FIG. 5. The ram '60 then remains in its upper position and downward drift thereof is prevented by the valve 92 and the choke-check valve 109.

In the FIG. system, the

check valves

65, 78, 93 and 103 may, if desired, be of the same form as

valves

67A, 67B, 71A and 71B, except that the pilot passages 73 will be plugged and the valve members 72 will have openings communicating the chambers 74 with the outlet ports.

We, therefore, particularly point out anddistinctly claim as our invention:

1. In a pressure controlled directional system of the type wherein a valve assembly is selectively operative to conduct fluid under pressure from a pump means to a fluid motor port or to conduct return flow of fluid from said motor port to a reservoir; said valve assembly comprising supply and return valves having inlet and outlet ports respectively communicating with said pump means and said motor port and with said motor port and said reservoir, and each of said supply and return valves having a valve member movable therein and having a first area on one side exposed to fluid pressure in said inlet port and a second larger area on the opposite side exposed to pilot pressure to close said valve; control means having communication with said pump means and said reservoir selectively to conduct pilot pressure therethrough into one valve to close it while pilot pressure in the other valve is vented to said reservoir via said control means whereby inlet pressure acting on said first area opens said other valve for flow of fluid to or from said motor port according to whether said other valve is said supply valve or said return valve and wherein said control means has a neutral position at which the pilot pressure in both valves is vented to said reservoir so that both valves are opened for flow of fluid from said pump means to said reservoir.

2. The system of claim 1 wherein said control means comprises a control valve having a control valve member selectively movable to supply or vent pilot pressure to or from said supply and return valves.

3. In a pressure controlled directional system of the type wherein a reversing valve assembly is selectively operative to conduct fluid under pressure from a pump means to either end of a double-acting fluid motor and to conduct return flow from the other end of said motor to a reservoir; said valve assembly comprising two s upply valves to supply fluid under pressure from said pump means to the respective ends of said motor and two return valves to conduct return flow from the respective ends of said motor to said reservoir; each valve being of the pressure-seated type wherein pilot pressure therewithin closes said valve and wherein the reduction of pilot pressure therewithin permits opening thereof for flow of fluid to said motor or return flow of fluid from said motor; a four-way valve having a pilot pressure port in communication with said pump means, a reservoir port in communication with said reservoir, and two control ports each communicated with a supply valve and a return valve associated with opposite ends of said motor, and having a valve member movable therein to alternately vent the pilot pressure of one of said supply valves to said reservoir for opening thereof to conduct fluid under pressure from said pump means into one end of said motor and to vent the pilot pressure of one of said return valves to said reservoir for opening thereof to conduct return fluid from the other end of said motor to said reservoir; said four-way valve member having a neutral position whereat both control ports are communicated with said reservoir port whereby said supply valves and said return valves are opened to conduct fluid from said pump means to said reservoir and whereat said pressure port is blocked whereby pilot pressure stands at said four-way valve preparatory to conduction through either control port.

4. The system of claim 3 wherein said pump means comprises a main pump to supply fluid under pressure to said motor through an open supply valve, and a pilot pump to supply pilot pressure to the pilot pressure port of said four-way valve; and wherein check valves between said pilot pump and pressure port and between said main pump and pressure port prevent reverse flow of fluid from said pilot pressure port annd enable supply of pilot pressure from said main pump in the event that pilot pressure is less than main pump pressure.

5. The system of claim 3 wherein a counterbalance valve between one end of said motor and the associated supply valve and return valve supports a load on said motor when said four-way valve member is in neutral position; and wherein a check valve bypasses said counterbalance valve to conduct fluid under pressure into said one end of said motor.

6. The system of claim 3 wherein an unloading valve between one end of said motor and the associated supply valve and return valve supports a load on said motor when said four way valve is in neutral position; wherein a first check valve lbypasses said unloading valve to conduct fluid under pressure into said one end of said motor; wherein a counterbalance valve and check valve between the ends of said motor also supports a load on said motor and permits return flow from said one end of said motor to flow into the other end of said motor to augment flow of fluid from said main pump via the thenopensupply valve until return flow pressure increases to a value to open said unloading valve.

7. The system of claim 3 wherein a rapid travel valve between the ends of said motor is operative selectively to conduct return flow from one end of said motor to said reservoir via said valve assembly or to the other end of said motor to augment the flow from said pump means.

8. A reversing valve assembly for a double-acting fluid motor comprising two pairs of valves, each valve being operative in response to a change of pilot pressure supplied to said valve, one pair of valves being supply valves having inlet ports for connection with a fluid pressure source and outlet ports for connection to the respective ends of a double-acting fluid motor, and the other pair of valves being return valves having inlet ports for connection to the respective ends of such motor and outlet ports for connection to a reservoir; each valve having a valve member which prevents or permits flow of fluid through said valve according to whether pilot pressure acting thereon is of high or low magnitude; and a fourway closed center pilot pressure control valve having a pilot pressure inlet port, a reservoir port, and a pair of control ports respectively connected to a supply valve and to a return valve associated with opposite ends of such motor, and having a control valve member movable therein from a neutral position whereat said pilot pressure inlet port is blocked and both control ports are communicated with said reservoir port whereby to permit opening of both supply valves and both return valves for flow of fluid from said pressure source to the reservoir to operating positions selectively communicating said control ports with said pilot pressure inlet port and with said reservoir port thus to establish pilot pressure of high or lower magnitude in said supply and return valves so that fluid under pressure through an open supply valve is conducted to one end of the motor and that return flow from the other end of the motor passes through the open return valve.

9. In a pressure controlled directional system of the type wherein a reversing valve assembly is selectively operative to conduct fluid under pressure from a pump means to either the rod or head end of a differential dis placement double-acting fluid motor and to conduct return flow from the other end of said motor to a reservoir; said valve assembly comprising two supply valves to supply fluid under pressure from said pump means to the respective ends of said motor and two return valves to conduct return flow from the respective ends of said motor to said reservoir; each valve being of the pressure-seated type wherein pilot pressure therewithin closes said valve and wherein the reduction of pilot pressure therewithin permits opening thereof for flow of fluid to said motor or return flow of fluid from said motor; a four-way valve having a pilot pressure port in communication with said pump means, a reservoir port in communication with said reservoir, and two control ports each communicated with a supply valve and a return valve associated with opposite ends of said motor, and having a valve member movable therein to alternately vent the pilot pressure of one of said supply valves to said reservoir for opening thereof to conduct fluid under pressure from said pump means into one end of said motor and to vent the pilot pressure of one of said return valves to said reservoir for opening thereof to conduct return fluid from the other end of said motor to said reservoir; first and second unloading valves each substantially the same as said supply and return valves respectively connected between the ends of said motor for return flow of fluid from the rod end of said motor to the head end via said first unloading valve when the latter is open and between the rod end of said motor and the associated supply valve and return valve for return flow of fluid through the latter when said second unloading valve is open; a check valve for bypassing said unloading valves to conduct fluid under pressure to the rod end of said motor; a pilot valve for selectively bleeding fluid from the chamber of either unloading valve and conducting pilot pressure to the chamber of the other unloading valve whereby when said second unloading valve is closed by pilot pressure, return flow of fluid from the rod end of said motor flows through said first unload- 10 ing valve to augment flow of fluid from said pump means to the head end of said motor and whereby when said first unloading valve is closed by pilot pressure, return flow of fluid from the rod end of said motor flows through said second unloading valve to the associated return valve.

10. The system of claim 9 wherein said four-way valve member is movable to a neutral position to vent the pilot pressure of both supply valves and both return valves to said reservoir for opening thereof to conduct fluid under pressure from said pump means to said reservoir; wherein a pilot operated relief valve between the rod end of said motor and the associated supply valve and return valve supports a load on said motor when said four-way valve member is in neutral position; and wherein said check valve bypasses said pilot operated relief valve to conduct fluid under pressure into the rod end of said motor when the associated supply valve is open; said pilot operated relief valve, when open, conducting return flow of fluid from the rod end of said motor through whichever unloading valve is open.

11. The system of claim 9 wherein said pump means comprises a dual pump including high pressure-low volume pump to supply pilot pressure to said four-way valve, and a low pressure-high volume pump to supply fluid pressure through a check valve for rapid actuation of said motor; and wherein a relief valve communicates with said high pressure-low volume pump such that when it is opened by an associated pilot relief valve it conducts high pressure fluid to said motor.

12. The system of claim 11 wherein an unloading valve substantially the same as said supply and return valves is operative, when open, to conduct fluid delivered by said low pressure-high volume pump to said reservoir thus to unload said pump and, when closed, to block communication of said low pressure-high volume pump with said reservoir thus to load said pump; and wherein an associated control valve conducts pilot pressure to said unload ing valve to close it or vents said pilot pressure from said unloading valve to permit opening thereof.

References Cited UNITED STATES PATENTS 1,558,002 10/1925 Ferris 91-468X 2,569,881 10/1951 Davies 91-454 2,800,110 7/1957 Haarmeyer 91452X 2,980,064 4/1961 Norton et al. 91-452X 3,151,455 10/1964 Tennis 91-454X 3,381,586 5/1968 Rosenberg 91446X 3,433,131 3/1969 Soyland et al. 91--454X 3,442,338 5/1969 Broderson 91-436X LAVERNE D. GEIGER, Primary Examiner E. J. EARLS, Assistant Examiner US. Cl. X.R. 91-461