US3927603A

US3927603A - Control means for a pair of fluid motors

Info

Publication number: US3927603A
Authority: US
Inventors: Gerald W Bernhoft
Original assignee: Koehring Co
Current assignee: Bank of New England NA
Priority date: 1972-06-12
Filing date: 1974-05-24
Publication date: 1975-12-23
Anticipated expiration: 1992-12-23

Abstract

A fluid pressure system comprising a pair of pilot actuated control valves, one of which has an inlet for pump output fluid and passage means through which the other is supplied with said pump fluid. Actuation of the valve element in said one control valve to a full operating position inhibits flow of pump output fluid to the other control valve until said valve element is returned at least part way toward its neutral position, and such partial return thereof is automatically effected as a consequence of actuation of the pilot for said other control valve.

Description

United States Patent Bernhoft CONTROL MEANS FOR A PAIR OF FLUID MOTORS 1 Dec. 23, 1975 3,773,084 11/1973 Bernhoft et 91/414 X Primary Examiner-Alan Cohan Assistant Examiner-Gerald A. Michalsky Attorney, Agent, or Firm-James E. Nilles ABSTRACT A fluid pressure system comprising a pair of pilot actuated control valves, one of which has an inlet for pump output fluid and passage means through which the other is supplied with said pump fluid. Actuation of the valve element in said one control valve to a full operating position inhibits flow of pump output fluid to the other control valve until said valve element is returned at least part way toward its neutral position, and such partial return thereof is automatically effected as a consequence. of actuation of the pilot for said other control valve. i j

5 Claims, 2 Drawing Figures STICK CONTROL VALVE M EXTEND U.S. Patent Dec. 23, 1975 Sheet 10f2 3,927,603

FIG. 1

I. i. w. 5 i i CONTROL MEANS FOR A PAIR OF FLUID MOTORS BACKGROUND OF THE INVENTION This application is a division of copending application Ser. No. 262,024 filed June 12, I972 which issued as US. Pat. No. 3,883,023 on May 13, 1975.

BACKGROUND OF THE INVENTION This invention relates to fluid pressure systems in which a pair of fluid motors must at times be operated simultaneously, in consequence of actuation of pressure compensated control valves therefor.

As is well known, when two such pressure compensated control valves are connected together in a bank having a common inlet or supply passage for pump output fluid, that valve which is closer to the inlet has priority over the other. This is to say that if the valve element or spool of the first control valve is in a full operating position, all of the pump output fluid entering the inlet would flow to the fluid motor governed by said first valve, and none would be available for operation of the motor governed by the second control valve. In that case, only one of the fluid motors could be operated at a time.

A hydraulically operated backhoe is but one example of a mechanism having two fluid motors, in this case double acting hydraulic cylinders, which frequently must be operated concurrently in order to efficiently perform its digging function. A first pressure compensated valve can be one which controls the bucket cylinder, and the second pressure compensated valve can be one which controls the stick cylinder. If the bucket control valve is nearer the inlet and is actuated to a full operating position, all of the pump flow is directed into the bucket cylinder, and operation of the stick cylinder is impossible.

Inasmuch as all control valves have a maximum capacity, one solution to the aforementioned problem would be to supply a volume of pressure fluid to the inlet of the valve bank in excess of the capacity of the first valve section. In this way, sufficient fluid could be made available for simultaneous operation of both the bucket and stick cylinders. This solution, however, is subject to the objection that additional horsepower would be required, which additional horsepower would be wasted when only one of the cylinders was in operation.

Another solution to the problem involves practice of an expedient which has for long been quite common to operators of parallel and/or series-parallel control valves. This expedient required the operator to manually return the valve element of the first control valve partway toward its neutral position, in order to divert some of the incoming pump fluid to the motor governed by the second control valve. For simultaneous operation of the bucket and the stick cylinders of a backhoe, therefore, the operator had to acquire a certain degree of skill in the manual manipulation of the hand levers on their respective control valves and he frequently had to "hunt" for the proper positions of both valve elements, by continuously shifting their levers back and forth to obtain the desired rates of fluid flow to the motors governed by the control valves.

SUMMARY OF THE INVENTION It is the purpose of the present invention to provide a fluid pressure system comprising a plural spool pilot operated control valve mechanism having a common pressure fluid supply passage for said spools, and wherein instrumentalities incorporated in the system function automatically to effect partial retraction from a full operating position of the valve element of a first control valve nearest the inlet of the supply passage, as a consequence of actuation of the valve element of a second control valve downstream from the first in the direction of fluid flow through the supply passage, to thereby make pressure fluid available to the service passages governed by the second control valve.

More specifically it is an object of the invention to provide a control valve mechanism comprising a pair of pilot operated control valves, wherein actuation of the pilot to effect shifting of one control spool to an operating position automatically effects retraction of the control spool nearer the inlet of the mechanism from a full flow operating position thereof partway toward a neutral position to thus enable flow of inlet fluid to service passage means governed by the downstream valve spool.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic view of a material handling device, such as a backhoe embodying this invention, and

FIG. 2 is a graphic diagram of a fluid pressure system employed in carrying out the invention.

DETAILED DESCRIPTION The invention is embodied in a material handling device, such as a backhoe illustrated in FIG. I, and including a boom I to which an arm or stick 2 is pivoted for relative movement. In addition, a tool, such as a bucket 3, is pivoted to the arm 2 for relative pivotal movement. A hydraulic cylinder A is connected between the tool 3 and the stick 2 which upon extension of the hydraulic cylinder A causes clockwise pivotal movement of the bucket 3 relative to the arm 2. A similar cylinder B is connected between the arm 2 and the boom 1 which acts a support so that extension of the hydraulic cylinder B causes the stick 2 to pivot in a clockwise direction relative to the boom I.

Referring now more particularly to FIG. 2, it will be seen that the system comprises a control valve mechanism 4 having a pressure fluid inlet 5, an outlet 6, and first and

second control valves

7 and 8 which can comprise two juxtaposed sections ofa bank whose inlet 5 is supplied with pressure fluid from the output port of a pump 9. The first control valve 7 is that which is nearer the inlet 5 and can be considered as the upstream valve for controlling the cylinder A in FIG. I. The second control valve 8 can thus be referred to as the second or downstream valve, for controlling the cylinder B. The valve 7 is connected by hydraulic lines 7a and 7b to the opposite ends of hydraulic cylinder A and valve 8 is connected by

hydraulic lines

80 and 8b to the opposite ends of hydraulic cylinder B.

Each of the control valves has been shown as of the pressure compensated type having a control spool which is movable out of its neutral position indicated in the diagram to operating positions at opposite sides of neutral. Fluid pressure operated actuators 10, one connected with each end of each spool, provides for shifting of the spools to one or the other of their respective operating positions at the dictate of pilot valves such as generally designated 1]. While each actuator has its own pilot valve 11, only two have been shown in the diagram, one for the actuator 10 at the left hand end of the upstream control valve 7, and one for the actuator 10 at the right hand end of the downstream control valve 8.

All of the pilot valves are connected with a common source of pilot fluid under pressure. For purposes of illustration the pilot fluid can comprise air under pressure brought in to the system through a duct 12. The pilot valves I] are of the type disclosed in detail in the US. Pat. No. 3,773,084 of Gerald W. Bernhoft and David A. Miller Ser. No. 195,58l, granted Nov. i0, I973 and entitled Control For Mobile Construction Machine. In fact, the pilot circuitry herein shown follows to a considerable extent that which is disclosed in said copending application.

Each pilot valve 11 has a plunger which is movable up and down and is normally held in a closed upper position blocking flow of air under pressure from the air line 12 to the actuators l0. Depression of the plunger of the pilot H for control valve 7 effects shifting of the spool thereof to a full operating position to the right of neutral by the actuator 10 at its left hand end; while depression of the plunger of the pilot H for control valve 8 effects shifting of its spool to a full operating position to the left of neutral by the actuator 10 at its right hand end.

With pressure compensated control valves like those graphically shown in the diagram, pressure fluid entering the inlet 5 from the pump 9 is able to flow substantially freely through a common supply passage such as indicated at 14 as long as the spools of both control valves remain in their neutral positions shown. Each one of the valves, when actuated separately to a full operating position at the dictate of its pilot 11, is capable of directing substantially the entire out-put of the pump 9 to the hydraulic cylinder A or B governed thereby.

However, as is the case with series-parallel valves, if the spool of the first or upstream control valve 7 is in a full operating position, it inhibits flow of supply fluid to the second or downstream control valve 8. As a result, the cylinder governed by the downstream control valve 8 cannot be operated until the spool of the upstream control valve 7 is returned to neutral, or at least partway toward neutral to a position metering flow to its associated cylinder and thereby allowing some of the pump output fluid entering the inlet 5 to flow to the downstream control valve 8 for operation of the cylinder governed thereby concurrently with the cylinder governed by the upstream control valve 7.

As explained in the aforesaid copending application, however, it is possible by manual regulation of the position of the plunger of pilot valve 11 for control valve 7 to place it in any one of a number of undefined positions intermediate its closed and fully open positions, to effect reduction of the air pressure in the associated actuator 10 to a value at which the force it exerts on the spool of valve 7 balances the force of the return spring [5 thereon at some metering position of the spool between its neutral and full flow positions. In this way part of the pump fluid entering the inlet 5 can flow to the cylinder governed by control valve 7 and the remainder can be made to flow to the cylinder governed by control valve 8.

According to this invention, the operator of apparatus, such as a backhoe, having the fluid pressure system herein illustrated, does not have to hunt for the intermediate position the plunger of pilot 11 for valve 7 must occupy in order to enable concurrent operation of the cylinders governed by the

control valves

7 and 8. For example, one of these cylinders can be that which governs the tilting and dumping motions of the bucket under the control of the upstream valve 7, and the other cylinder can be that which is governed by the downstream control valve 8 and effects the dig and extend motions of the stick upon which the bucket is mounted.

If it is assumed that the plunger is held in a fully depressed position in the pilot I] for the upstream control valve 7, so that the spool thereof will accordingly be in a full flow bucket tilt position at which all of the pump output fluid entering the inlet 5 flows to the bucket cylinder, the operator can automatically effect partial retraction of said spool and operation of the stick cylinder to cause digging motion of the stick concurrently with tilting motion of the bucket merely by actuation of the pilot 11 for the right hand actuator N) of the downstream control valve 8.

A full discussion of the pilot circuitry which follows, is necessary to an understanding of how this desired concurrent operation of the cylinders governed by both control valves is achieved without any repositioning of the plunger in the pilot for the bucket control valve 7.

The pilot circuit for the actuator 10 at the left hand end of the bucket control valve 7 will be first described. Air under pressure of about psi in line 12 enters a reducing valve 17 and flows therefrom to the inlet of pilot ll via a duct 18 at a pressure of about 35 psi. An outlet duct 19 leads from the pilot valve and is connected with an amplifier 20 ofa commercially available type manufactured by the Bellofram Corp. and known as its Model 360 relay.

The pressure in the duct 19 can be anywhere from 5 to 35 psi, depending upon the extent to which the plunger of the pilot valve 11 has been depressed. This pressure is controlled by bypassing incoming air to the atmosphere in an amount which decreases with downward motion of the pilot plunger until its fully open position is reached at the end of the plunger stroke.

Depending upon the pressure of the air entering the relay or amplifier 20, the pressure of the air flowing into a duct 21 from the outlet of the relay will vary from about l5 to 90 psi. For the purposes of this invention the duct 2i can be considered as a fluid pressure supply line for the actuator 10 at the left hand end of the bucket control valve 7.

If only that pilot valve governing bucket tilt is actuated to a full flow position, pilot fluid (air) in the supply duct 21 normally flows through the left hand section 22 of a two position three port valve instrumentality 23 to a duct 24 connecting with the valve actuator 10, to subject the same to the full pressure of pilot fluid in duct 21. This, of course, effects shifting of the spool in the bucket control valve 7 to a full operating position to the right of neutral, against the force of its return spring 15.

The two position valve instrumentality 23 is biased to the position described above by a spring 25. It is also provided with a fluid pressure actuator 29 in the form of an air cylinder which, when connected with a source of air under pressure, effects shifting of said valve instrumentality to its other position to communicate the duct 24 with a duct 26 forming a branch of the supply duct 2].

An adjustable pressure regulating valve 27 in branch 28 of the supply duct is normally set to reduce the pressure of pilot fluid flowing to the actuator through the valve instrumentality 23 to a value such as to allow the spring to retract the spool of the bucket control valve 7 partway toward neutral, to a position at which the fluid pressure force exerted on the spool by the left hand actuator 10 balances the return force exerted on the spool by the spring 15.

By way of example, with a spring 15 of given strength, and with the pressure of pilot fluid in the supply duct 21 at a maximum value of about 90 psi, and assuming that the valve instrumentality 23 has been actuated to its position routing pilot fluid to the actuator duct 24 through the pressure regulating valve 27, the pressure of fluid then entering duct 24 will be about 52 psi. In other words, the opposing forces of spring pressure on one end of the bucket spool and of pilot actuator pressure on the other end of the spool will hold the spool in a metering position such as to make pump fluid available to the spool of the stick cylinder 8.

It should be noted that the pressure regulating valve 27 is of the self relieving type so as to dissipate any of the higher pressure air from the actuator 10 when the valve instrumentality 23 is shifted to its last described position.

It should also be understood that a duplicate of the pilot valve 11 and pilot circuitry described is provided for the actuator 10 at the right hand end of the bucket control valve 7, to govern dump.

The valve instrumentality 23 will be shifted to its position routing pilot fluid through the pressure regulating valve 27 as a consequence of actuation of the pilot valve 11 for either actuator 10 of the stick control valve 8. The pilot circuitry for each actuator 10 of the stick control valve is the same as that described except that the pressure regulating valve 27 and fluid pressure actuated valve instrumentality 23 are eliminated therefrom.

For convenience, only that pilot valve 11 and pilot circuitry which controls the actuator 10 for the dig" function of the stick control valve has been illustrated. Manual depression of the plunger of the pilot valve ll for dig" brings fluid (air) under pressure into the pilot supply duct 121. This duct leads to the actuator 10 at the right hand end of the stick control valve and it also has a branch 30 which leads through a shuttle valve 31 to a control duct 32 connecting with the fluid pressure actuator 26 for the two position valve instrumentality 23.

Accordingly, if the bucket control spool is in its full flow tilt position directing the entire pump output to the bucket cylinder at the time the plunger of the pilot valve 11 is depressed to effect actuation of the stick control valve for the dig" function, the resulting pressurization of duct 121 with pilot fluid will effect actuation of the valve instrumentality 23 and disconnection of the actuator l0 for the bucket control valve from its supply duct 21, and pilot fluid will be routed to said actuator at reduced pressure through the regulator 27 and the two position valve instrumentality 23.

The spool of the bucket control valve 7 then assumes an intermediate or metering position at which part of the pump fluid entering the inlet 5 of the control valve mechanism is directed to the bucket cylinder and the remainder is directed to the stick cylinder. In this way, the bucket and stick cylinders can be operated simultaneously, to effect the desired digging action through the combined tilt and dig movements of the bucket and stick, respectively.

From this it will be seen that the adjustment of the pressure regulating valve 27 will determine how much pump output fluid will be diverted to the stick cylinder with a return spring 15 of given strength acting upon the spool of the upstream control valve 7.

The same retracting motion of the spool in the bucket control valve takes place upon depression of the plunger in the pilot valve (not shown) for the actuator 10 at the left hand end of the stick control valve. In that event, the actuator 26 for the two position valve instrumentality is again pressurized by pilot fluid (air) under pressure in the actuator supply duct 221 through a branch 35 connecting it with the actuator through the shuttle valve 31 and the duct 32.

From the foregoing description, together with the accompanying drawing, it will be readily apparent to those skilled in the art that this invention provides a fluid pressure system which automatically provides for partial retraction of the spool of a first pilot operated control valve from a full flow position, to enable simultaneous operation of two fluid motors, as a consequence of actuation of a pilot valve for a second control valve; and that adjustable instrumentalities incorporated in the system provide for such simultaneous operation of the fluid motors at optimum speeds without the necessity for repositioning of their pilot valves during such operation.

It will be further apparent that this invention is applicable to pilot operated control valve systems regardless of whether the pilot valves and circuits governed thereby employ air or hydraulic fluid; and that the pilot valves themselves can be solenoid operated in some installations where remote control of the pilot valves is desired.

1 claim:

I. A fluid pressure system of the type wherein pressure fluid from a source is directed to a fluid motor in consequence of pilot actuation by a pilot valve of the valve element of one control valve to an operating position provided the valve element of another pilot operated control valve is in either a neutral position or has been displaced from neutral in one direction, against spring bias, partway toward a full flow operating position characterized by:

A. means providing a pair of fluid pressure actuators,

one for each control valve and operatively connected with the valve element thereof;

B. a pilot circuit for each actuator the pilot circuit for said other control valve having a fluid pressure supply duet With a branch leading therefrom;

C. a valve instrumentality normally occupying a position connecting the actuator for said other control valve with said duct, said valve instrumentality being movable to another position to communicate said last named actuator with said duct through said branch thereof;

D. a pressure control instrumentality in said branch rendered operative in said other position of said valve instrumentality effect subjection of the actuator for said other control valve to pressure at a value less than that present in said supply duct and so preselected that said pressure control instrumentality is cooperable with the spring bias on the valve element of said other control valve to hold the valve element thereof in a position between its said neutral and full operating positions;

E. and means for effecting actuation of said valve instrumentality to said other position thereof in response to a signal produced as a consequence of actuation of said pilot valve for said one control valve.

2. A fluid pressure operated system wherein actua- A. a fluid pressure operated valve actuator for each control valve;

B. a pilot circuit for each actuator, the pilot circuit for the actuator of said first control valve comprising high and low pressure ducts, said high pressure duct serving as means through which pilot fluid under pressure can be supplied to said first control valve at a value such that the resulting actuating force exerted on the valve element overcomes said spring bias and causes the valve element to be moved to said full flow operating position thereof; said low pressure duct serving as a means through which pilot fluid under pressure can be supplied to said first control valve at a lower value such that the resulting actuating force exerted on the valve element will equal the spring bias thereon at one of 45 said flow metering positions of the valve element;

C. fluid pressure actuatable valve means normally occupying a position communicating the actuator for said first control valve with said high pressure duct, said valve means being movable to another position communicating said last named actuator with the low pressure duct;

D. and means for effecting actuation of said valve means to its said other position in consequence of a fluid pressure signal derived from the pilot circuit for the actuator of said second control valve.

3. A fluid pressure system of the type having a first pilot operated control valve with a valve element movable in one direction against spring bias from a neutral position through a range of flow metering positions to a full flow operating position directing pump output fluid from an inlet to a service passage in said first control valve, said system further having a second pilot operated control valve and a common pressure fluid supply passage for said control valves through which fluid flow to said second control valve is inhibited as a consequence of actuation of said valve element of said first control valve to said full flow operating position thereof, each control valve being provided with a pilot valve for effecting operation of its actuator, characterized by:

A. a first fluid pressure actuator operable by a first pilot valve for effecting movement of said valve element in said direction and a second fluid pressure actuator for operating said second control valve;

B. first duct means through which pilot fluid under pressure can be supplied to said first actuator at a value such that the resulting actuating force exerted on the valve element overcomes said spring bias and causes the valve element to be moved to said full flow operating position thereof;

C. second duct means through which pilot fluid under pressure can be supplied to said first actuator at a lower value such that the resulting actuating force exerted on the valve element will equal the spring bias thereon at one of said flow metering positions of the valve element;

D. a valve instrumentality normally occupying a first position connecting said first actuator with said first duct means but movable to a second position connecting said first actuator with said second duct means; and

E. means for actuating said valve instrumentality to said second position thereof in consequence of actuation of the pilot valve for said second control valve.

4. The fluid pressure system of claim 3 further characterized by:

A. said second duct means having a branch connected with with first duct means to be supplied with pilot fluid under pressure therefrom;

B. and a pressure reducing valve instrumentality in said branch.

5. The fluid pressure system of claim 4, further characterized by:

A. said first control valve having a supply passage connecting with said inlet and into which pump fluid is bypassed in the neutral and flow metering position of its valve element;

8. said second pilot operated control valve having an inlet connected with said supply passage to be supplied with pump output fluid therefrom;

C. and said valve instrumentality being actuatable to said second position thereof by pressure fluid from the pilot valve governing said second control valve.

* I? k I

Claims

1. A fluid pressure system of the type wherein pressure fluid from a source is directed to a fluid motor in consequence of pilot actuation by a pilot valve of the valve element of one control valve to an operating position provided the valve element of another pilot operated control valve is in either a neutral position or has been displaced from neutral in one direction, against spring bias, partway toward a full flow operating position characterized by: A. means providing a pair of fluid pressure actuators, one for each control valve and operatively connected with the valve element thereof; B. a pilot circuit for each actuator, the pilot circuit for said other control valve having a fluid pressure supply duct with a branch leading therefrom; C. a valve instrumentality normally occupying a position connecting the actuator for said other control valve with said duct, said valve instrumentality being movable to another position to communicate said last named actuator with said duct through said branch thereof; D. a pressure control instrumentality in said branch rendered operative in said other position of said valve instrumentality effect subjection of the actuator for said other control valve to pressure at a value less than that present in said supply duct and so preselected that said pressure control instrumentality is cooperable with the spring bias on the valve element of said other control valve to hold the valve element thereof in a position between its said neutral and full operating positions; E. and means for effecting actuation of said valve instrumentality to said other position thereof in response to a signal produced as a consequence of actuation of said pilot valve for said one control valve.

2. A fluid pressure operated system wherein actuation of pilot valve effects movement of the valve element of a first control valve in one direction from neutral, against spring bias, through a range of metering positions to a full operating position, and wherein a second pilot actuated control valve is rendered ineffective until said valve element is returned at least partway toward its neutral position, characterized by: A. a fluid pressure operated valve actuator for each control valve; B. a pilot circuit for each actuator, the pilot circuit for the actuator of said first control valve comprising high and low pressure ducts, said high pressure duct serving as means through which pilot fluid under pressure can be supplied to said first control valve at a value such that the resulting actuating force exerted on the valve element overcomes said spring bias and causes the valve element to be moved to said full flow operating position thereof; said low pressure duct serving as a means through which pilot fluid under pressure can be supplied to said first control valve at a lower value such that the resulting actuating force exerted on the valve element will equal the spring bias thereon at one of said flow metering positions of the valve element; C. fluid pressure actuatable valve Means normally occupying a position communicating the actuator for said first control valve with said high pressure duct, said valve means being movable to another position communicating said last named actuator with the low pressure duct; D. and means for effecting actuation of said valve means to its said other position in consequence of a fluid pressure signal derived from the pilot circuit for the actuator of said second control valve.

3. A fluid pressure system of the type having a first pilot operated control valve with a valve element movable in one direction against spring bias from a neutral position through a range of flow metering positions to a full flow operating position directing pump output fluid from an inlet to a service passage in said first control valve, said system further having a second pilot operated control valve and a common pressure fluid supply passage for said control valves through which fluid flow to said second control valve is inhibited as a consequence of actuation of said valve element of said first control valve to said full flow operating position thereof, each control valve being provided with a pilot valve for effecting operation of its actuator, characterized by: A. a first fluid pressure actuator operable by a first pilot valve for effecting movement of said valve element in said direction and a second fluid pressure actuator for operating said second control valve; B. first duct means through which pilot fluid under pressure can be supplied to said first actuator at a value such that the resulting actuating force exerted on the valve element overcomes said spring bias and causes the valve element to be moved to said full flow operating position thereof; C. second duct means through which pilot fluid under pressure can be supplied to said first actuator at a lower value such that the resulting actuating force exerted on the valve element will equal the spring bias thereon at one of said flow metering positions of the valve element; D. a valve instrumentality normally occupying a first position connecting said first actuator with said first duct means but movable to a second position connecting said first actuator with said second duct means; and E. means for actuating said valve instrumentality to said second position thereof in consequence of actuation of the pilot valve for said second control valve.

4. The fluid pressure system of claim 3 further characterized by: A. said second duct means having a branch connected with with first duct means to be supplied with pilot fluid under pressure therefrom; B. and a pressure reducing valve instrumentality in said branch.

5. The fluid pressure system of claim 4, further characterized by: A. said first control valve having a supply passage connecting with said inlet and into which pump fluid is bypassed in the neutral and flow metering position of its valve element; B. said second pilot operated control valve having an inlet connected with said supply passage to be supplied with pump output fluid therefrom; C. and said valve instrumentality being actuatable to said second position thereof by pressure fluid from the pilot valve governing said second control valve.