Hydraulic control valve and pressure compensating mechanism therefor

Claim 2

A control valve having a body with inlet and feeder passage means, a pair of service passages, and a valve element having a pair of working positions at opposite sides of a neutral position at which inlet fluid flows thereacross from the feeder passage means to a selected one of said pair of service passages, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to a selected one of the seRvice passages via the feeder passage means in accordance with variations in the pressure differential across the valve element in a selected one of said working positions thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means, said passageway comprising a hollow portion of said plunger; C. a single check valve disposed in said hollow portion of said plunger and arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. said pressure compensating valve mechanism being located in the path along which pressure fluid flows from the inlet passage means to the feeder passage means; E. the plunger of said pressure compensating valve mechanism being spring urged in a direction to increase inlet fluid flow to the feeder passage means; F. and means providing for imposition of a fluid pressure force on the plunger which varies in accordance with the pressure of fluid in the inlet passage means and opposes said spring force on the plunger.

Claim 3

The control valve of claim 1, wherein said last named means comprises: A. a surface on the plunger; B. and means for translating the pressure of fluid in said plunger passageway into said fluid pressure force on said surface of the plunger.

Claim 4

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism located in the path along which pressure fluid flows from the inlet passage means to the feeder passage means and having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway, said passageway comprising a hollow portion of the plunger through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve located in the hollow portion of said plunger and being arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. said plunger of said pressure compensating valve mechanism being spring urged in a direction to increase inlet fluid flow to the feeder passage means; E. means providing for imposition of a fluid pressure force on the plunger which varies in accordance with the pressure of fluid in the inlet passage means and opposes said spring force on the plunger. F. said last named means comprising a surface on the plunger; G. and means for translating the pressure of fluid in the feeder passage means into said fluid pressure force on the plunger.

Claim 5

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism located in the path along which pressure fluid flows from the inlet passage means to the feeder passage means and having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway, said passageway comprising a hollow portion of the plunger through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve located in the hollow portion of said plunger and being arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. said plunger of said pressure compensating valve mechanism being spring urged in a direction to increase inlet fluid flow to the feeder passage means; E. means providing for imposition of a fluid pressure force on the plunger which varies in accordance with the pressure of fluid in the inlet passage means and opposes said spring force on the plunger. F. said last named means comprising a surface on the plunger; G. and means for translating the pressure of fluid in the feeder passage means into said fluid pressure force on the plunger.

Claim 6

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway, said passageway comprising a hollow portion of the plunger having axially spaced inlet and outlet ports in the wall of said hollow plunger portion to respectively communicate with the inlet and feeder passage means; C. a check valve being located in said hollow portion of the plunger For engagement with an annular seat in said passageway, coaxial therewith, and being arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. a first surface on the plunger upon which pressure fluid from the inlet passage means exerts force tending to move the plunger in one direction to effect reduction in flow of fluid from the inlet passage means to the feeder passage means; E. a second surface on the plunger upon which pressure fluid can exert force tending to move the plunger in the opposite direction to effect increase in flow of fluid from the inlet passage means to the feeder passage means; F. and feedback duct means controlled by the valve element and rendered effective in said working position thereof to impose the pressure of service passage fluid on said second surface of the plunger.

Claim 7

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway, said passageway comprising a hollow portion of the plunger having axially spaced inlet and outlet ports in the wall of said hollow plunger portion to respectively communicate with the inlet and feeder passage means; C. a check valve being located in said hollow portion of the plunger For engagement with an annular seat in said passageway, coaxial therewith, and being arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. a first surface on the plunger upon which pressure fluid from the inlet passage means exerts force tending to move the plunger in one direction to effect reduction in flow of fluid from the inlet passage means to the feeder passage means; E. a second surface on the plunger upon which pressure fluid can exert force tending to move the plunger in the opposite direction to effect increase in flow of fluid from the inlet passage means to the feeder passage means; F. and feedback duct means controlled by the valve element and rendered effective in said working position thereof to impose the pressure of service passage fluid on said second surface of the plunger.

Claim 8

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. means providing a feedback passageway controlled by the valve element, through which service passage pressure can be imposed on the plunger tending to shift the same in the direction to increase fluid flow from the inlet passage means to the feeder passage means in said working position of the valve element; E. a surface on the plunger upon which pressure fluid can exert force tending to shift the plunger in the opposite direction to reduce fluid flow from the inlet passage means to the feeder passage means; F. and means providing a second passageway through which said plunger surface can be subjected to the pressure of fluid in the feeder passage means.

Claim 9

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. means providing a feedback passageway controlled by the valve element, through which service passage pressure can be imposed on the plunger tending to shift the same in the direction to increase fluid flow from the inlet passage means to the feeder passage means in said working position of the valve element; E. a surface on the plunger upon which pressure fluid can exert force tending to shift the plunger in the opposite direction to reduce fluid flow from the inlet passage means to the feeder passage means; F. and means providing a second passageway through which said plunger surface can be subjected to the pressure of fluid in the feeder passage means.

Claim 10

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. means by which the pressure of fluid in the feeder passage means can be imposed upon the plunger to effect movement thereof in the direction to reduce fluid flow from the inlet passage means to the feeder passage means; E. a surface on the plunger upon which pressure fluid can exert force tending to effect movement thereof in the opposite direction to increase fluid flow from the inlet passage means to the feeder passage means; F. and means providing a feedback passage through which the pressure of fluid in the service passage can be imposed upon said plunger surface in the working position of the valve element. 7. A control valve having a body with inlet and feeder passage means, a pair of service passages, and a valve element movable from one to the other of a pair of working positions at opposite sides of a neutral position to communicate either of said pair of service passages with the feeder passage means and the other with return passage means, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to one of the service passages via the feeder passage means in accordance with variations in the pressure differential across the valve element in one of said working positions thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. an outlet in the body to which inlet fluid flows in bypass relation to the feeder passage via passage defining means in the compensating plunger when the valve element is in said neutral position; E. a second such control valve having its inlet connected to said inlet to receive pressure fluid therefrom; F. and said outlet in the first designated control valve being communicated with one of said return passages thereof whereby the second control valve can be supplied with exhaust fluid from a fluid motor governed by the first designated control valve at times when said outlet is in communication with said one return passage.

Claim 11

A control valve having a body with inlet and feeder passage means, a service passage, and a valve element having a working position at which inlet fluid flows thereacross from the feeder passage means to the service passage, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to the service passage via the feeder passage means in accordance with variations in the pressure differential across the valve element in said working position thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. means by which the pressure of fluid in the feeder passage means can be imposed upon the plunger to effect movement thereof in the direction to reduce fluid flow from the inlet passage means to the feeder passage means; E. a surface on the plunger upon which pressure fluid can exert force tending to effect movement thereof in the opposite direction to increase fluid flow from the inlet passage means to the feeder passage means; F. and means providing a feedback passage through which the pressure of fluid in the service passage can be imposed upon said plunger surface in the working position of the valve element. 7. A control valve having a body with inlet and feeder passage means, a pair of service passages, and a valve element movable from one to the other of a pair of working positions at opposite sides of a neutral position to communicate either of said pair of service passages with the feeder passage means and the other with return passage means, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to one of the service passages via the feeder passage means in accordance with variations in the pressure differential across the valve element in one of said working positions thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. an outlet in the body to which inlet fluid flows in bypass relation to the feeder passage via passage defining means in the compensating plunger when the valve element is in said neutral position; E. a second such control valve having its inlet connected to said inlet to receive pressure fluid therefrom; F. and said outlet in the first designated control valve being communicated with one of said return passages thereof whereby the second control valve can be supplied with exhaust fluid from a fluid motor governed by the first designated control valve at times when said outlet is in communication with said one return passage.

Claim 12

A control valve having a body with inlet and feeder passage means, a pair of service passages, and a valve element having a pair of working positions at opposite sides of a neutral position at which inlet fluid flows thereacross from the feeder passage means to a selected one of said pair of service passages, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to a selected one of the service passages via the feeder passage means in accordance with variations in the pressure differential across the valve element in a selected one of said working positions thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a single check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. pressure chambers into which the opposite ends of the compensating plunger project to act as pistons therein; E. pressure of fluid in one of said chambers tending to effect movement of the plunger in the direction to increase fluid flow from the inlet passage means to the feeder passage means, and pressure of fluid in the other chamber tending to effect movement of the plunger in the direction to decrease fluid flow from the inlet passage means to the feeder passage means; F. signal passage means governed by the valve element and rendered effective thereby in its said working position, to communicate the selected one of said service passages with said one chamber; G. means providing a passageway communicating said other chamber with the inlet passage means; H. means in the body providing a low pressure passage; I. and vent means controlled by the valve element and rendered effective thereby in a non-working position thereof to communicate said one chamber with the low pressure passage.

Claim 13

A control valve having a body with inlet and feeder passage means, a pair of service passages, and a valve element having a pair of working positions at opposite sides of a neutral position at which inlet fluid flows thereacross from the feeder passage means to a selected one of said pair of service passages, characterized by: A. a pressure compensating valve mechanism having a fluid pressure responsive plunger to regulate such flow of inlet fluid to a selected one of the service passages via the feeder passage means in accordance with variations in the pressure differential across the valve element in a selected one of said working positions thereof; B. means in the plunger defining a passageway through which pressure fluid from the inlet passage means must flow in order to reach the feeder passage means; C. a single check valve arranged to pass pressure fluid from the inlet passage means to the feeder passage means but to block reverse flow therefrom to the inlet passage means; D. pressure chambers into which the opposite ends of the compensating plunger project to act as pistons therein; E. pressure of fluid in one of said chambers tending to effect movement of the plunger in the direction to increase fluid flow from the inlet passage means to the feeder passage means, and pressure of fluid in the other chamber tending to effect movement of the plunger in the direction to decrease fluid flow from the inlet passage means to the feeder passage means; F. signal passage means governed by the valve element and rendered effective thereby in its said working position, to communicate the selected one of said service passages with said one chamber; G. means providing a passageway communicating said other chamber with the inlet passage means; H. means in the body providing a low pressure passage; I. and vent means controlled by the valve element and rendered effective thereby in a non-working position thereof to communicate said one chamber with the low pressure passage.

Claim 14

The control valve of claim 8, further characterized by: A. said body providing part of a sectional control valve and having a surface adapted for mating engagement with a surface on another section of the valve; B. and said vent means comprising a groove in said surfAce of the body.

Claim 15

A control valve having fluid supply and return passage means, feeder passage means, a service passage, and a movable valve element to communicate the supply passage means with the service passage via said feeder passage means in a working position of the valve element and to close off the service passage from the feeder and return passage means in a non-working position of the valve element, characterized by the following: A. pressure compensating valve mechanism having a feedback chamber and a fluid pressure responsive plunger one end of which is received in the feedback chamber so that the plunger can be actuated in one direction by pressure of feedback fluid in the chamber to effect increase in fluid flow from the supply passage means to the feeder passage means, said plunger having a surface upon which fluid from the supply passage means can exert force tending to move the plunger in the opposite direction, to reduce fluid flow to the feeder passage means; B. said control including a body comprising adjoining body sections having mating surfaces in intimate engagement with one another, and said valve element and passage means being located in one of said body sections; C. venting passage means including a groove in one of said mating surfaces through which said feedback chamber is vented in the non-working position of the valve element; D. and signal passage means comprising a portion of said groove, for communicating the service passage with the feedback chamber in said working position of the valve element.

Claim 16

A control valve having fluid supply and return passage means, feeder passage means, a service passage, and a movable valve element to communicate the supply passage means with the service passage via said feeder passage means in a working position of the valve element and to close off the service passage from the feeder and return passage means in a non-working position of the valve element, characterized by the following: A. pressure compensating valve mechanism having a feedback chamber and a fluid pressure responsive plunger one end of which is received in the feedback chamber so that the plunger can be actuated in one direction by pressure of feedback fluid in the chamber to effect increase in fluid flow from the supply passage means to the feeder passage means, said plunger having a surface upon which fluid from the supply passage means can exert force tending to move the plunger in the opposite direction, to reduce fluid flow to the feeder passage means; B. said control including a body comprising adjoining body sections having mating surfaces in intimate engagement with one another, and said valve element and passage means being located in one of said body sections; C. venting passage means including a groove in one of said mating surfaces through which said feedback chamber is vented in the non-working position of the valve element; D. and signal passage means comprising a portion of said groove, for communicating the service passage with the feedback chamber in said working position of the valve element.

Claim 17

Pressure compensating valve mechanism wherein an elongated fluid pressure actuatable valve plunger is movable axially in a valve compartment in the body of the mechanism to regulate fluid flow through said compartment from inlet means opening thereto, to a pair of outlets opening therefrom, in accordance with variations in the pressure differential across the ends of the plunger, characterized by the following: A. said compartment providing valve actuating chambers into which the opposite ends of the plunger project; B. a spring in one of said chambers acting on the adjacent end of the plunger to yieldingly urge the same in a direction to decrease flow of fluid from the inlet means to one of said outlets and to simultaneously increase flow of fluid from the inlet means to the other outlet; C. means in the body providing a first passage communicating with the other chamber and through which fluid pressure force which varies in accordance with the pressure at the inlet means can be imposed upon the plunger in opposition to the spring force thereon; D. a second passage in the body leading to the spring chamber and providing for imposition on the plunger of a fluid pressure signal force which augments the spring force on the plunger; E. means providing a passageway which leads through an internal portion of the plunger, and through which pressure fluid from the inlet means must flow in order to reach said other outlet; F. and a check valve in said passageway arranged to pass fluid to said other outlet but to block reverse flow from said other outlet to the inlet means.

Claim 18

Pressure compensating valve mechanism wherein an elongated fluid pressure actuatable valve plunger is movable axially in a valve compartment in the body of the mechanism to regulate fluid flow through said compartment from inlet means opening thereto, to a pair of outlets opening therefrom, in accordance with variations in the pressure differential across the ends of the plunger, characterized by the following: A. said compartment providing valve actuating chambers into which the opposite ends of the plunger project; B. a spring in one of said chambers acting on the adjacent end of the plunger to yieldingly urge the same in a direction to decrease flow of fluid from the inlet means to one of said outlets and to simultaneously increase flow of fluid from the inlet means to the other outlet; C. means in the body providing a first passage communicating with the other chamber and through which fluid pressure force which varies in accordance with the pressure at the inlet means can be imposed upon the plunger in opposition to the spring force thereon; D. a second passage in the body leading to the spring chamber and providing for imposition on the plunger of a fluid pressure signal force which augments the spring force on the plunger; E. means providing a passageway which leads through an internal portion of the plunger, and through which pressure fluid from the inlet means must flow in order to reach said other outlet; F. and a check valve in said passageway arranged to pass fluid to said other outlet but to block reverse flow from said other outlet to the inlet means.

Claim 19

The pressure compensating valve mechanism of claim 11, further characterized by: A. the passageway through said internal portion of the plunger being coaxial therewith and including radial inlet and outlet ports which open through the wall of said plunger portion at axially spaced locations, for communication with the inlet means and said other outlet, respectively; B. and means on the plunger in said internal portion thereof providing an annular valve seat located between said inlet and outlet ports and facing the latter, which seat is engageable by the check valve to prevent flow of fluid from said outlet port to the inlet port.

Claim 20

A control valve instrumentality having an inlet, an outlet, an open center passage connecting the inlet with the outlet, a pair of valve spools, one upstream from the other, each movable to an operating position to communicate an associated motor port with a feeder passage, and a pair of pressure compensating valve mechanisms, one for each valve spool, mounted in bores which are serially intersected by the open center passage and each having a plunger movable in a direction to establish communication of the associated feeder passage with the adjacent upstream portion of the open center passage in consequence of subjection of one end of the plunger to the pressure of fluid in the associated motor port when the latter is in communication with its associated feeder passage, characterized by: A. the upstream one of said plungers being incapable of restricting the open center passage and consequently incapable of effecting build up in pressure in the upstream portion of the open center passage when in position communicating the latter with the associated feeder passage; B. the other plunger having means thereon to effect restriction of the open center passage when moved in the direction to communicate the adjacent upstream portion thereof with the associated feeder passage; C. and means operable to subject said end of said other plunger to the pressure of fluid in the motor port associated with the upstream plunger in said operating position of the upstream one of said valve spools.

Claim 21

A control valve instrumentality having an inlet, an outlet, an open center passage connecting the inlet with the outlet, a pair of valve spools, one upstream from the other, each movable to an operating position to communicate an associated motor port with a feeder passage, and a pair of pressure compensating valve mechanisms, one for each valve spool, mounted in bores which are serially intersected by the open center passage and each having a plunger movable in a direction to establish communication of the associated feeder passage with the adjacent upstream portion of the open center passage in consequence of subjection of one end of the plunger to the pressure of fluid in the associated motor port when the latter is in communication with its associated feeder passage, characterized by: A. the upstream one of said plungers being incapable of restricting the open center passage and consequently incapable of effecting build up in pressure in the upstream portion of the open center passage when in position communicating the latter with the associated feeder passage; B. the other plunger having means thereon to effect restriction of the open center passage when moved in the direction to communicate the adjacent upstream portion thereof with the associated feeder passage; C. and means operable to subject said end of said other plunger to the pressure of fluid in the motor port associated with the upstream plunger in said operating position of the upstream one of said valve spools.

Claim 22

A control valve as set forth in claim 13, wherein said last named means comprises passage means extending through an internal portion of the downstream valve spool.

Claim 23

The control valve instrumentality of claim 13, further characterized by: A. a pressure chamber into which said end of said other plunger projects to act as a piston therein; B. said last named means comprising passage means which leads from the motor port associated with the upstream plunger to said pressure chamber; C. and a shuttle valve governing flow through said passage means, and arranged to preclude reverse flow of pressure fluid from said pressure chamber toward the motor port associated with the upstream plunger.

Claim 24

A control valve instrumentality having an inlet, and outlet, an open center passage connecting the inlet with the outlet, a pair of valve spools, one upstream from the other, each movable to an operating position to communicate an associated motor port with a feeder passage, and a pair of pressure compensating valve mechanisms, one for each valve spool, mounted in bores which are serially intersected by the open center passage and each having a plunger movable in a direction to establish communication of the associated feeder passage with the adjacent upstream portion of the open center passage in consequence of subjection of one end of the plunger to the pressure of fluid in the associated motor port when the latter is in communication with its associated feeder passage, characterized by: A. said plungers being incapable of restricting the open center passage and consequently incapable of effecting buildup in pressure in the open center passage when in position communicating their respective upstream open center passage portions with their associated feeder passages; B. a third plunger which extends across the open center passage downstream from the first designated plungers and has means thereon to restrict or even block flow therethrough upon movement of said third plunger in one direction; C. and means operable at times when either of said motor ports is in communication with its associated feeder passage, for translating the pressure of feeder passage fluid in said motor port into a force on said third plunger that is effective to move the same in said direction to restrict the open center passage.

Claim 25

A control valve instrumentality having an inlet, and outlet, an open center passage connecting the inlet with the outlet, a pair of valve spools, one upstream from the other, each movable to an operating position to communicate an associated motor port with a feeder passage, and a pair of pressure compensating valve mechanisms, one for each valve spool, mounted in bores which are serially intersected by the open center passage and each having a plunger movable in a direction to establish communication of the associated feeder passage with the adjacent upstream portion of the open center passage in consequence of subjection of one end of the plunger to the pressure of fluid in the associated motor port when the latter is in communication with its associated feeder passage, characterized by: A. said plungers being incapable of restricting the open center passage and consequently incapable of effecting buildup in pressure in the open center passage when in position communicating their respective upstream open center passage portions with their associated feeder passages; B. a third plunger which extends across the open center passage downstream from the first designated plungers and has means thereon to restrict or even block flow therethrough upon movement of said third plunger in one direction; C. and means operable at times when either of said motor ports is in communication with its associated feeder passage, for translating the pressure of feeder passage fluid in said motor port into a force on said third plunger that is effective to move the same in said direction to restrict the open center passage.

Claim 26

The control valve instrumentality of claim 16, further characterized by: A. a pressure chamber into which one end of said third plunger projects to have said force imposed thereon; B. said last named means comprising passage means which leads from each Of said motor ports to said chamber; C. and a shuttle valve actuatable by pressure fluid in the downstream motor port at a value greater than that of pressure fluid in the upstream motor port to a position closing off communication between the upstream motor port and said chamber.