US3575212A

US3575212A - Leakage control for closed center valves

Info

Publication number: US3575212A
Authority: US
Inventors: Raud A Wilke
Original assignee: Koehring Co
Current assignee: Husco International Inc
Priority date: 1969-11-03
Filing date: 1969-11-03
Publication date: 1971-04-20
Anticipated expiration: 1988-04-20
Also published as: BE753810A; DE2049876A1; NL7015680A; FR2071625A5; GB1303328A; DE2049876C3; DE2049876B2; SE361919B

Abstract

A hydraulic control valve wherein pressure fluid which leaks along the exterior of the movable valve element from a high pressure inlet zone is intercepted before it reaches any service passage of the valve and conducted along a path externally of the valve element to a low pressure return passage in the valve body.

Description

Raud A. Wilke United States Patent s T N m MA 8 mm MA .mfl D E W N U M U a W M w w m B r m n e V m 137/625 48X 137/625.69X l37/625.69X

[211 App]. No. 873,521

[22] Filed Nov. 3, 1969 [45] Patented Apr. 20, 1971 [73] Assignee Koehring Company Milwaukee, Wis.

VALVES ABSTRACT: A hydraulic control valve wherein pressure fluid which leaks along the exterior of the movable valve element 137/625.69 from a high pressure inlet zone is intercepted before it reaches Fl6lk 11/07 any service passage of the valve and conducted along a path externally of the valve element to a low pressure return passage in the valve body.

18 Claims, 2 Drawing Figs.

[51] Int..

FIG-.I.

PATENTE D APR 2 0 van SHEET 1 OF 2 NVENTOR 7 A- zZka E Y ATTOR EZY FIG-.2.

PATENTED APR20 I97:

SHEET 2 OF 2 INVENTOQ.

Ewliaud Aj/ili A-r-ro NE;

LEAKAGE COUL FOR CLUSED CENTER VALVES This invention relates to hydraulic control and has more particular reference to control valves of the closed center, hold-in-neutral type.

The valve element of a hold-in-neutral control valve prevents operation of a fluid motor governed thereby in the neutral position of the valve element in its chamber, at which it blocks flow of pressure fluid to and from the motor. Because there is no provision for pump output fluid entering the inlet chamber of a closed center control valve such as herein concerned to be returned to a reservoir through an open center passage in the valve body, fluid in the inlet chamber of the valve remains at high pressure all during the time the pump is in operation and the valve element is in neutral. Thus pressure ,fluid at high pressure is immediately available for operation of the motor upon shifting of the valve element to one of its operating positions.

One of the problems encountered with closed center valves of this type resulted from the impossibility of fitting the valve element in its chamber or bore closely enough to prevent fluid at high pressure in the inlet chamber of the valve from leaking along the wall of the bore, past the lands on the valve element in the neutral or hold position thereof, to a service port and thence to the governed motor. Such leakage has caused unwanted operation of the governed motor, and has created conditions that could become dangerous to life as well as to costly hydraulically actuated apparatus' With this problem in mind, it is a general object of the invention to provide a closed center control valve of the character described wherein the danger of unwanted motor operation due to leakage thereto of high pressure fluid past the valve element of the control valve is obviated.

Hence, it is a more specific purpose of this invention to provide a closed center control valve of the character described wherein the problem referred to above is solved by intercepting such leakage fluid before it reaches a service passage to which the motor is connected, and by conducting such intercepted leakage fluid to a low pressure return passage in the body of the valve.

in the most specific sense, it is an object of the invention to provide a closed center control valve of the character described wherein such leakage fluid is exhausted to a low pressure passage along a path lying wholly externally of the valve element so as to obviate the need for costly machining thereof, and which path is chiefly comprised of cored passages in the body of the control valve.

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 such changes in the specific apparatus disclosed herein may be made as come within the scope of the appended claims.

The accompanying drawing illustrate two complete examples of the embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

H6. 1 is a sectional view of a closed center control valve embodying this invention; and

FIG. 2 is a sectional view of a closed center control valve similar to that seen in H6. 1, but illustrating a modified embodiment of the invention.

Referring now to the accompanying drawings, FIG. 1 illustrates a closed center hydraulic control valve having a body 5 with a bore 6 therein defining a valve chamber. An elongated valve element or spool 7 is closely fitted in the bore for lengthwise sliding movement therein between a neutral or hold position shown, and a pair of operating positions at opposite sides of its neutral position.

The control valve chosen for illustration is intended to govern the operation of a double acting cylinder or other reversible fluid motor (not seen), although it will be appreciated that this invention is equally as well applicable to control valves for single acting service. For double acting service, the body of the valve is provided with a pair of upwardly opening service passages 8 and 9 which are connectable with the opposite ends of the cylinder, and which communicate with the valve chamber or bore 6 at zones that are spaced apart a substantial distance along its axis. These passages are selectively communicable with a pressure fluid source, such as a pump 10, by means of the valve spool 7, in one or the other of its operating positions.

The output of the pump is fed into an inlet chamber in the body of the valve, here shown by way of example as comprised of twin branches 11 and 12 which open to the bore 6 at locations spaced apart axially thereof from one another and intermediate the zones at which the service passages communicate with the bore. As is customary in control valves heretofore available, the valve spool 7 is adapted to communicate the service passage 8 with the right-hand inlet branch 12 when the valve spool is shifted to its operating position to the right of neutral, and to communicate service passage 9 with the left-hand inlet branch 11 when the spool is shifted to its operating position to the left of neutral. In each of these operating positions, the spool is adapted to communicate the service passage not connected with the inlet chamber with an exhaust or return passage 13.

The valve spool 7 has five circumferential grooves therein, at axially spaced apart locations, and which, reading from left to right, are numbered l4, 15, 16, 17 and 18. In the neutral position of the spool shown, its groove 14 is in register with the junction between the bore and service passage 8, while its groove 17 is in register with the junction between the bore and service passage 9. The grooves 14 and 17 provide for communicating the service passages 8 and 9 with either the inlet chamber or the return passage 13, depending upon the direction the valve spool is shifted out of its neutral position.

Besides the service passages 8 and 9, the valve body is provided with a number of other passages through portions of which pressure fluid can flow to and from the service passages in the different operating positions of the valve spool. These include the exhaust passage 13 mentioned previously, which can be considered as a low pressure bridge of U-shaped configuration, having a bight portion 20 that extends lengthwise of the bore 6 a distance therebelow, and substantially parallel opposite legs which define

exhaust branches

21 and 22 that extend upwardly from the opposite ends of the bight portion and intersect the bore 6 at zones spaced outwardly along the bore from its zones of communication with the service passages 8 and 9, respectively, so as to receive return fluid from said service passages through the grooves 14 and 17 in the spool.

A bridge passage 24 to supply high pressure fluid to the service passages is also formed in the body. The high pressure supply bridge is of inverted U-shaped providing a bight portion 25 which extends lengthwise of the bore 6, a distance thereabove, and

opposite legs

26 and 27 which extend downwardly from the ends of the bight portion to the bore 6 at locations intermediate the service passages 8 and 9. The leg 26 is adjacent to passage 6 and provides for supplying pressure fluid thereto through spool groove 14; while the leg 27 is adjacent to passage 9 to provide for supply of pressure fluid thereto through spool groove 17. The two branches 11 and 12 of the inlet chamber open to the bore 6 at zones between those at which the high pressure bridge legs 26 and 27 communicate with the bore.

Substantially medially between the inlet branches 11 and 12, a short feeder passage 30 extends upwardly from the bore toward the bight portion 25 of the high pressure bridge 24. This feeder passage is communicated with the high pressure bridge through a check valve 31 in a passageway 32 that joins the feeder passage 30 with the left-hand leg 26 of the bridge. The check valve 31 is a so-called load holding check valve which is arranged to open only at times when pressure of fluid in feeder passage 30 exceeds the pressure of fluid in the high pressure bridge 24. The feeder passage 30 opens to the bore 6 at a zone which is in register with the groove 16 in the valve spool when the spool is in its neutral position.

Feeder passage 1%) is communicated with the inlet branch 12 when the valve spool is shifted to its operating position to the right of neutral so that pump fluid can then flow to service passage 8 via the left-hand leg of the bridge 24. Similarly, passage 30 cooperates with bridge 24 to supply service passage 9 from inlet branch 11 when the valve spool is shifted to its operating position to the left of neutral.

in the well known open center valves commonly used in the past, one or the other, or both of the inlet branches l1 and 12 were communicated in some way with an outlet passage 35 in the neutral position of the valve spool. The outlet passage 35 is here shown as located substantially centrally of the valve body, between the bore 6 and the bight position 20 of the low pressure bridge 13, and it is at all times communicated with the latter through a short connecting passageway 35'.

In the control valve here shown, however, the

lands

36 and 37 on the spool 7 defined by its grooves l5, l6 and 17, close off the inlet branches l1 and 12 from the bore 6 in the neutral position of the valve spool. Accordingly, as long as the pump 10 remains in operation, its full output pressure will obtain in the inlet branches 11 and 12 and such fluid can leak along the wall of the bore 6 through the slight clearance space essential to assure proper sliding of the spool therein, toward one or the other of the service passages 8 or 9. If nothing is done to prevent it, such leakage fluid can seep lengthwise along the exterior of the spool to one of the service passages 8 or 9 and cause unwanted operation of the fluid motor governed by the control valve. Such unwanted operation of the fluid motor can at times be dangerous, even through the motor will then operate at only a slow speed.

According to this invention, any high pressure fluid that leaks along the wall of the bore 6 from the inlet branch 11 in a direction toward the service passage 8 in the neutral position of the valve spool will be intercepted at the junction between the bore and the inner end of a venting passage 40 which has its outer end in communication with the outlet passage 35. The inner end of the passage 40 opens to the bore 6 at a location between itsjunctions with the inlet branch 11 and the left-hand leg 26 of the high pressure bridge passage 24, and so as to be in register with the groove 15 in the valve spool in the neutral position of the latter. Hence, any fluid that leaks along the wall of the bore from the inlet branch 11 toward the service passage 8 will be intercepted before it reaches said service pasage, and be conducted to the outlet passage 35 through the venting passage 40.

At this point, it is important to observe that in the neutral position of the valve spool, its groove 15 is located to communicate the left-hand branch 26 of the high pressure bridge with the venting passage 40. Accordingly, any high pressure fluid in the inlet branch 12 that leaks along the wall of the bore 6 toward the other service passage 9 will be intercepted by and collect in the right-hand leg 27 of the high pressure bridge, from whence it will be free to flow through the remainder of said bridge and spool groove 15 to venting passage 40, and thence to the outlet passage 35.

in like manner, the high pressure bridge is employed to conduct to the venting passage 40 any fluid that leaks out of the inlet branches 11 and/or 12 into the feeder passage 30. High pressure leakage fluid in feeder passage 30 will be able to flow through passageway 32 and check valve 31 therein to the left-hand leg 26 of the high-pressure bridge, and from there across the spool groove 15 to the outlet passage 35 via passage 40.

From the above, it will be apparent that the high-pressure bridge, through which pressure fluid must flow to reach the service passages in the working positions of the valve spool, is vented in the neutral position of the spool. It thus constitutes a low pressure bridge in the neutral position of the valve spool, and it only becomes a high pressure bridge when the valve spool is moved to one or the other of its operating positions. At those times the bridge 24 is cut off from the venting passage 40 either by the spool land 36 or by the land 42 thereon defined by spool grooves 14 and 15.

It is also important to realize that because of the above described arrangement, a more or less conventional passage in the valve body which is normally relied upon to conduct high pressure fluid to one of the service passages in an operating position of the valve spool is here capable of use in conducting leakage fluid to the reservoir in the neutral position of the valve spool.

An important feature of this invention resides in the fact that the groove 18 in the valve spool 7 enables the spool to be placed in a float position when it is shifted to the left far enough to communicate the service passages 8 and 9 with one another through the low

pressure bridge branches

21 and 22.

The present leakage controlled closed center valve construction enables this float position to be achieved in a most facile manner, whereas float was either impossible or extremely difficult and costly to obtain in the past with comparable valve constructions. This resulted from the fact that in past closed center valves, the junctions of the service passages with the bore were customarily communicated with the return passages in the neutral position of the valve spool, thus making it essential to provide complicated and costly pilot operated mechanisms to isolate the ports of the controlled fluid motor from the reservoir.

The closed center control valve illustrated in FIG. 2 has several features in common with that described above. lt has a bore 6 with a valve spool 70 therein, but the spool has five annular grooves which, reading from left to right, are numbered 45, 46, 47, 48 and 49. These grooves define lands 50 and 51 at opposite sides of groove 45; lands 52 and 53 at opposite sides of groove 47; and lands 54 and 55 at opposite sides of groove 49.

The valve has an inlet chamber with but a single feeder branch 56 that opens to the bore 6 in register with the spool groove 47 in the neutral position of the spool shown, midway between the

legs

26 and 27 of the high pressure bridge 24.

In this case, when the valve spool is in neutral, the spool lands 52 and 53 block flow of fluid into the bore 6 from the

legs

26 and 27 of the high pressure bridge; while the

lands

51 and 54 extend across the junctions of the service passages 8 and 9 with the bore to prevent flow of fluid therethrough to and from the service passages.

To achieve the purpose of this invention in the valve of FIG. 2, its body is provided with a pair of small U-shaped cores, 76 and 77, associated with the service passages 8 and 9, respectively. The bight portion of the core 76 extends lengthwise of the bore 6, beneath the zone at which the service passage 8 joins with the bore but above the bight portion of the return passage 13. The opposite legs 78 and 79 of core 76 extend upwardly from its bight to intersect the bore 6 at opposite sides of the service passage 8. The left-hand leg is positioned to be intennediate the service passage 8 and the adjacent exhaust branch 21, in register with spool groove 45', while the right-hand leg 79 is positioned to be intermediate the service passage 8 and the adjacent leg 26 of the high-pressure bridge 24, in register with spool groove 46.

Similarly, the U-shaped core 77 has opposite legs 80 and 81 which intersect bore 6 and lie at opposite sides of service passage 9, with the leg 80 intermediate said service passage and the adjacent leg 27 of the high pressure bridge, in register with spool groove 80; while the leg 81 is intermediate service passage 9 and the adjacent leg 22 of the low pressure bridge, in register with spool groove 49. The bight of the core 77 joins the lower ends its legs 80 and 81, below the bore 6 but above the bight of the low-pressure bridge 13.

The inlet branch 56 is communicated through a passageway 82 and a load holding check valve 83 with the bight of the high-pressure bridge 24.

As before, the valve spool 70 is shiftable out of its neutral position shown at each of a pair of operating positions at opposite sides of neutral, to effect communication of either service passage 8 or 9 with the inlet branch 56 via the high pressure bridge, and to effect communication of the other service passage with the outlet passage 35 via the low-pressure bridge 13.

For example, if the service passage 8 is to be communicated with the inlet or feeder passage 56, and service passage 9 is to be concurrently connected with the return passage 13, the valve spool 70 must be shifted to its operating position to the right of its neutral position. When so shifted, high-pressure fluid in the inlet or feeder 56 can flow past the check valve 83 into the high-pressure bridge 24, through its leg 26 and spool groove as into the leg 79 of cored passage 76, and through the leg 7% thereof and spool groove 45 to service passage 8. Pressure fluid returning to service passage 9 from the controlled motor flows through spool groove 48 into leg 80 of core 77, and through leg M and spool groove 49 to branch 22 of the low pressure bridge 13.

Fluid flow to and from the service passages is reversed when the valve spool is shifted to its operating position to the left of neutral.

The same small U-shaped cores 76 and 77 which provide important segments of the paths along which pressure fluid flows both to and from the service passages 8 and 9 in the operating positions of the valve spool, also comprise the means for conducting to the return passage 13 high-pressure fluid that leaks axially outwardly along the wall of the bore 6 from the inlet branch as in the neutral position of the valve spool.

All such leakage fluid flowing along the wall of the bore to one or the other, or both, of the small U-shaped cores 76-77, enters their legs 79 or 8th closest to the high pressure bridge legs 26-27, and flows to the upright branches 21-22 of the low-pressure bridge 13 through the remote legs 78 and 81 of said cores. In other words, the cores 76 and 77 conduct the leakage fluid to the low-pressure bridge 113, in bypass relation to the spool lands 5i and 54 that close off the service passages h and 9 from the bore.

From the foregoing description, together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides a closed center valve in which lwkage fluid from the inlet chamber of the valve is led to a return or outlet passage through duct means no part of which is comprised of drilled passages in the valve spool, and which duct means can comprise parts of the paths along which pressure fluid flows to and from the service passages of the valve.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

lclaim:

l. A closed center hydraulic control valve having a body with a service passage that is selectively communicable with either an inlet or an outlet passage in one or the other of a pair of operating positions of a valve element in a chamber in which the valve element operates, and wherein said service passage is closed off from both the inlet and the outlet passage by the valve element in a neutral position thereof, characterized by:

A. said inlet and service passages opening to the valve chamber at zones spaced from one another;

IB. supply passage means having a portion communicating with said chamber at a location intermediate said zones, and through which pressure fluid from the inlet passage must flow to reach the service passage in one of said operating positions of the valve element; and

C. means defining a vent passage in the valve body, which opens to said chamber and which is cooperable with the valve element in the neutral position thereof to conduct to the outlet passage pressure fluid that leaks along the wall of said chamber from the inlet passage toward the zone at which the service passage opens thereto.

2. A closed center control valve, characterized by:

A. a body having a valve chamber therein;

l3. service, inlet and outlet passages in the body, opening to said chamber at spaced apart locations;

C. a valve element in said chamber adapted to close off the inlet passage from the outlet passage in a neutral position of the valve element at which it is adapted to also close off the service passage from both the inlet and outlet passages, said valve element being adapted to effect communication of the service passage selectively with either the inlet or the outlet passage in different operating positions of the valve element;

D. a supply passage which opens to said chamber and is adapted to conduct pressure fluid from the inlet passage to the service passage in one of said operating positions of the valve element; and

E. vent passage means which extends through a portion of the body from the outlet passage toward the valve chamber and intersects the latter at a location between its junction with the service and inlet passages, said vent' passage being cooperable with the valve element in the neutral position thereof to conduct to the outlet passage pressure fluid from the inlet passage that leaks along the wall of the valve chamber toward its junction with the service passage.

3. A closed center control valve of the type having a body with a valve element which is operable to effect communication, through a chamber in which the valve element operates, of a service passage with either a pressure fluid supply passage or with an outlet passage in one or the other of a pair of operating positions to which the valve element is movable, characterized by:-

A. means on the valve element operable in a hold position thereof to close off the service passage from both the supply and the outlet passages, and to also close off the supply passage from the outlet passage; and

B. vent passage means in the body comprising a branch of the outlet passage wholly externally of the valve element, said vent passage means intersecting the valve chamber at a location ahead of its junction with the service passage, with respect to the direction that fluid from the inlet passage tends to leak toward the service passage along the exterior of the valve element, so as to intercept such leakage fluid and prevent it from reaching the service passage.

4. A closed center hydraulic control valve of the type having a body with a service passage that is selectively communicable with either an inlet passage or with an outlet passage in one or the other of a pair of operating positions of a valve element in a chamber in which the valve element operates, and wherein said service passage is closed off from both the inlet and the outlet passage by the valve element in a neutral position thereof, characterized by:

A. said inlet and service passages communicating with the valve chamber at zones spaced from one another;

B. supply passage means having a portion communicating with said chamber at a location intermediate said zones, and through which inlet fluid must flow to reach the service passage in one of said operating positions of the valve element, said supply passage means registering with a groove in the exterior of the valve element in the neutral position thereof; and

C. means in the valve body defining a vent passage opening to said chamber and registering with said groove in the neutral position of the valve element, to communicate said supply passage means with the outlet passage along a path wholly externally of the valve element.

5. A control valve of the type having a body with an inlet, an outlet, supply passage means, a movable valve element, and a service passage which is selectively communicable with either the inlet or the outlet by the valve element, characterized by:

A. the supply passage means comprising a supply branch through which the inlet is communicated with the service passage by the valve element in one working position thereof, said supply branch being closed off from the inlet and from the service passage in a hold position of the valve element at which. it closes off the service passage from the outlet;

for the interception of any high pressure fluid that leaks past the valve element from the inlet or from the supply passage means in said hold position of the valve element, and being adapted to freely conduct all such intercepted leakage fluid to the outlet so as to prevent flow of said said feeder passage being normally closed off from both inlet branches by the valve spool but being communicable with different ones thereof in said operating positions of the spool; and

C. a check valve controlled passage in the body, through which pressure fluid received in the feeder passage from one or the other of said inlet branches can flow to the high pressure supply passage.

10. ln a closed center control valve having a body with a bore and an elongated valve spool slidable endwise in the bore from a neutral closed center position to each of a pair of operating positions to selectively communicate either of a pair of service passages with pressure fluid inlet means and the other service passage with outlet means characterized by:

leakage fluid to the service passage.

6. A closed center control valve of the type having a body with inlet and outlet passages, a service passage, a valve chamber with which said passages communicate at zones spaced from one another, and a movable valve element in said chamber to control communication of the service passage with the inlet and outlet passages, characterized by:

A. said valve element being adapted in a hold position thereof to close off communication of the service passage with both the inlet and the outlet passages, and being adapted to communicate the service passage with either the inlet or the outlet passage in one or the other of a pair of operating positions to which the valve element is movable; and

B. duct means rendered operative by the valve element in said hold position thereof for conducting to the outlet passage, in bypass relation to the service passage, pressure fluid from the inlet passage which leaks along the exterior of the valve element toward the service passage, said duct means being located entirely externally of the valve element and leading from a zone of said chamber between the zones at which said inlet and service passages communicate with said chamber.

7. A closed center valve having a body with a bore and an elongated valve spool in the bore movable from a hold position to a pair of operating positions to selectively communicate either of a pair of service passages with inlet means and the other service passage with return means, characterized by:

A. the service passages opening to the bore at first zones spaced apart axially of the bore;

B. a high-pressure supply passage through which pressure fluid from the inlet means is caused to flow to one of said service passages in each of said operating positions of the valve spool, said supply passage having a pair of branches, one for each service passage, and which branches open to the bore at second zones intermediate but axially adjacent to said first zones; and

C. a venting passage in the valve body, wholly externally of 55 A. said service passages opening to the bore at first zones spaced apart lengthwise of the bore;

B. said inlet means opening to the bore intermediate said first zones;

C. a supply passage through which the service passages are communicated with the inlet means by the valve spool in said operating positions thereof, said supply passage having a pair of branches, one for each service passage, and opening to the bore at second zones each adjacent to but between one of said first zones and the junction of the bore with the inlet means;

D. said outlet means comprising a return passage having a pair of branches, one for each service passage, said branches intersecting the bore at third zones each of which is adjacent to one of said first zones but at the side thereof remote from the adjacent second zone, and an outlet passage which is communicated with both of said return branches; and

E. a venting passage at all times connecting with said outlet means and with the bore, and cooperating with the valve spool in the neutral position thereof to vent one of said branches of the supply passage.

11. The closed center control valve of claim 10, wherein said venting passage opens to the bore at a location between the inlet means and one of said second zones and is communicated with said one branch of the supply passage through a groove in the valve spool and the bore in which the spool operates.

12. The closed center control valve of claim 11, further characterized by:

the valve spool, to nonnally communicate the highpressure supply passage with the return means, said venting passage opening to the bore at a location intermediate said second zones but adjacent to one of them, and being cooperable with the valve spool in the neutral position thereof to communicate one branch of and an elongated valve spool slidable axially therein from a closed center neutral position to each of a pair of operating positions to communicate either of a pair of service passages with centrally disposed inlet means and the other service passage with outlet means through grooves in the valve spool and portions of the bore, characterized by:

the supply passage with the return means through the bore in which the valve spool operates.

8. The closed center control valve of claim 7, wherein said inlet means is at all times communicable with the supply passage through a check valve arranged to pass pressure fluid into the supply passage; and wherein said inlet means opens to the bore at a location between said second zones.

9. The closed center control valve of claim 7, further characterized by:

A. said inlet means comprising a pair of inlet branches which open to the bore at axially spaced locations intennediate said second zones;

B. a feeder passage in the body, intersecting said bore at a location between its junctions with said inlet branches, 75

A. the outlet means being centrally located in the body, at

one side of the bore;

B. the service passages extending from the other side of the bore and intersecting the same at first zones which are spaced in axially opposite directions from the inlet means;

C. a pair of U-shaped bridge passages in the body, each having opposite branches that intersect the bore at axially opposite sides of one of said first zones, and a bight at the same side of the bore as the outlet means;

D. a U-shaped supply passage that embraces the inlet means and into which pressure fluid is caused to flow therefrom by the valve spool in either of its operating positions, said supply passage having opposite branches that intersect the bore at spacedlocations axially inwardly from the bridge passages, and a bight at the side of the bore remote from the outlet means; i

a U-shaped return passage in the body, having opposite branches, one for eachof said bridge passages, said return passage branches intersecting the bore at zones axially outwardly of the bridge passages and having a bight joining its branches and extending substantially lengthwise of the bore at the same side thereof as the outlet means but spaced farther from the bore than the outlet means and the bights of the bridge passages;

F. a passageway communicating the bight of the return passage with the outlet means; and

G. in its neutral position, the valve spool having 1. lands that close off communication of the service passages and the supply passage branches with the bore,

2. grooves that communicate theaxially remote branches of said bridge passages with the branches of the return passage, through the bore in which the spool operates,

3. and grooves that register with the innermost branches of the bridge passages.

14. The closed'center control valve of claim 13, wherein said inlet means intersects the bore intermediate the branches of the supply passage.

15. A hydraulic control valve having a' body with a bore, and an elongated valve element shiftable in said bore to diflerent positions to selectively communicate fluid flow passages in the body with one another, wherein said fluid flow passages provide:

v A. a pair of service passages that open from one side of the bore at first zones spaced apart lengthwise of the bore;

B. a supply passage having a pair of branches, one for each service passage, and which branches open to the bore at second zones located axially inwardly of said first zones;

C. a return passage having a pair of branches, one for each service passage, and which return branches open to the bore at third zones located axially outwardly of said first zones;

D. inlet passage means providing for flow of supply fluid to the service passages via said supply passage under the control of the valve element, said inlet passage means intersecting the bore between the supply passage lL branches; and

E. vent means intersecting the bore at zones axially inwardly of said first zones and cooperable with the valve element in the neutral position thereof to conduct leakage fluid from the inlet passage means to the return passage along a path wholly externally of the valve element.

16. The hydraulic control valve of claim 15, further characterized by:

A. said service passages opening uninterruptedly to one side of the body from said bore;

B. means on the valve element rendering said vent means 4 operable only in the neutral position of the valve element;

and

C. means on the valve element operable in one position thereof to communicate said service passages with one another.

17. The hydraulic control valve of claim [6, wherein the valve element is operable to effect communication of the service passages with one another through the return passage.

18. A closed center control valve of the type having a body with a valve element which is operable to effect communication, through a chamber in which the valve B. vent passa e' means in the body l. coopera le with the valve element in the neutral position thereof to intercept pressurized supply fluid that leaks along the wall of the chamber before such leakage fluid reaches the junction between the chamber and the service passage, for conducting such.

intercepted pressure fluid to the outlet passage,

2. and said vent passage being cooperable with the valve element to conduct pressurized supply fluid to the service passage in one of said operating positions of the valve element.

Claims

1. A closed center hydraulic control valve having a body with a service passage that is selectively communicable with either an inlet or an outlet passage in one or the other of a pair of operating positions of a valve element in a chamber in which the valve element operates, and wherein said service passage is closed off from both the inlet and the outlet passage by the valve element in a neutral position thereof, characterized by: A. said inlet and service passages opening to the valve chamber at zones spaced from one another; B. supply passage means having a portion communicating with said chamber at a location intermediate said zones, and through which pressure fluid from the inlet passage must flow to reach the service passage in one of said operating positions of the valve element; and C. means defining a vent passage in the valve body, which opens to said chamber and which is cooperable with the valve element in the neutral position thereof to conduct to the outlet passage pressure fluid that leaks along the wall of said chamber from the inlet passage toward the zone at which the service passage opens thereto.

2. A closed center control valve, characterized by: A. a body having a valve chamber therein; B. service, inlet and outlet passages in the body, opening to said chamber at spaced apart locations; C. a valve element in said chamber adapted to close off the inlet passage from the outlet passage in a neutral position of the valve element at which it is adapted to also close off the service passage from both the inlet and outlet passages, said valve element being adapted to effect communication of the service passage selectively with either the inlet or the outlet passage in different operating positions of the valve element; D. a supply passage which opens to said chamber and is adapted to conduct pressure fluid from the inlet passage to the service passage in one of said operating positions of the valve element; and E. vent passage means which extends through a portion of the body from the outlet passage toward the valve chamber and intersects the latter at a location between its junction with the service and inlet passages, said vent passage being cooperable with the valve element in the neutral position thereof to conduct to the outlet passage pressure fluid from the inlet passage that leaks along the wall of the valve chamber toward its junction with the service passage.

2. grooves that communicate the axially remote branches of said bridge passages with the branches of the return passage, through the bore in which the spool operates,

3. A closed center control valve of the type having a body with a valve element which is operable to effect communication, through a chamber in which the valve element operates, of a service passage with either a pressure fluid supply passage or with an outlet passage in one or the other of a pair of operating positions to which the valve element is movable, characterized by: A. means on the valve element operable in a hold position thereof to close off the service passage from both the supply and the outlet passages, and to also close off the supply passage from the outlet passage; and B. vent passage means in the body comprising a branch of the outlet passage wholly externally of the valve element, said vent passage means intersecting the valve chamber at a location ahead of its junction with the service passage, with respect to the direction that fluid from the inlet passage tends to leak toward the service passage along the exterior of the valve element, so as to intercept such leakage fluid and prevent it from reaching the service passage.

4. A closed center hydraulic controL valve of the type having a body with a service passage that is selectively communicable with either an inlet passage or with an outlet passage in one or the other of a pair of operating positions of a valve element in a chamber in which the valve element operates, and wherein said service passage is closed off from both the inlet and the outlet passage by the valve element in a neutral position thereof, characterized by: A. said inlet and service passages communicating with the valve chamber at zones spaced from one another; B. supply passage means having a portion communicating with said chamber at a location intermediate said zones, and through which inlet fluid must flow to reach the service passage in one of said operating positions of the valve element, said supply passage means registering with a groove in the exterior of the valve element in the neutral position thereof; and C. means in the valve body defining a vent passage opening to said chamber and registering with said groove in the neutral position of the valve element, to communicate said supply passage means with the outlet passage along a path wholly externally of the valve element.

5. A control valve of the type having a body with an inlet, an outlet, supply passage means, a movable valve element, and a service passage which is selectively communicable with either the inlet or the outlet by the valve element, characterized by: A. the supply passage means comprising a supply branch through which the inlet is communicated with the service passage by the valve element in one working position thereof, said supply branch being closed off from the inlet and from the service passage in a hold position of the valve element at which it closes off the service passage from the outlet; B. return passage means through which the service passage is communicable with the outlet in a second working position of the valve element but which is closed off from the service passage in said hold position of the valve element; and C. a passageway in the body through which said supply passage means is communicated with the outlet by the valve element, externally of the latter, in said hold position of the valve element, said passageway providing for the interception of any high pressure fluid that leaks past the valve element from the inlet or from the supply passage means in said hold position of the valve element, and being adapted to freely conduct all such intercepted leakage fluid to the outlet so as to prevent flow of said leakage fluid to the service passage.

6. A closed center control valve of the type having a body with inlet and outlet passages, a service passage, a valve chamber with which said passages communicate at zones spaced from one another, and a movable valve element in said chamber to control communication of the service passage with the inlet and outlet passages, characterized by: A. said valve element being adapted in a hold position thereof to close off communication of the service passage with both the inlet and the outlet passages, and being adapted to communicate the service passage with either the inlet or the outlet passage in one or the other of a pair of operating positions to which the valve element is movable; and B. duct means rendered operative by the valve element in said hold position thereof for conducting to the outlet passage, in bypass relation to the service passage, pressure fluid from the inlet passage which leaks along the exterior of the valve element toward the service passage, said duct means being located entirely externally of the valve element and leading from a zone of said chamber between the zones at which said inlet and service passages communicate with said chamber.

7. A closed center valve having a body with a bore and an elongated valve spool in the bore movable from a hold position to a pair of operating positions to selectively communicate either of a pair of service passages with inlet means and the oTher service passage with return means, characterized by: A. the service passages opening to the bore at first zones spaced apart axially of the bore; B. a high-pressure supply passage through which pressure fluid from the inlet means is caused to flow to one of said service passages in each of said operating positions of the valve spool, said supply passage having a pair of branches, one for each service passage, and which branches open to the bore at second zones intermediate but axially adjacent to said first zones; and C. a venting passage in the valve body, wholly externally of the valve spool, to normally communicate the high-pressure supply passage with the return means, said venting passage opening to the bore at a location intermediate said second zones but adjacent to one of them, and being cooperable with the valve spool in the neutral position thereof to communicate one branch of the supply passage with the return means through the bore in which the valve spool operates.

9. The closed center control valve of claim 7, further characterized by: A. said inlet means comprising a pair of inlet branches which open to the bore at axially spaced locations intermediate said second zones; B. a feeder passage in the body, intersecting said bore at a location between its junctions with said inlet branches, said feeder passage being normally closed off from both inlet branches by the valve spool but being communicable with different ones thereof in said operating positions of the spool; and C. a check valve controlled passage in the body, through which pressure fluid received in the feeder passage from one or the other of said inlet branches can flow to the high pressure supply passage.

10. In a closed center control valve having a body with a bore and an elongated valve spool slidable endwise in the bore from a neutral closed center position to each of a pair of operating positions to selectively communicate either of a pair of service passages with pressure fluid inlet means and the other service passage with outlet means characterized by: A. said service passages opening to the bore at first zones spaced apart lengthwise of the bore; B. said inlet means opening to the bore intermediate said first zones; C. a supply passage through which the service passages are communicated with the inlet means by the valve spool in said operating positions thereof, said supply passage having a pair of branches, one for each service passage, and opening to the bore at second zones each adjacent to but between one of said first zones and the junction of the bore with the inlet means; D. said outlet means comprising a return passage having a pair of branches, one for each service passage, said branches intersecting the bore at third zones each of which is adjacent to one of said first zones but at the side thereof remote from the adjacent second zone, and an outlet passage which is communicated with both of said return branches; and E. a venting passage at all times connecting with said outlet means and with the bore, and cooperating with the valve spool in the neutral position thereof to vent one of said branches of the supply passage.

12. The closed center control valve of claim 11, further characterized by: A. the branches of said supply passage being connected with one another at one side of The bore; B. the branches of said return passage being connected by a return passage portion which extends generally lengthwise of the bore at its opposite side; and C. said outlet passage being located between the bore and said passage portion that connects the branches of the return passage.

13. A closed center control valve having a body with a bore and an elongated valve spool slidable axially therein from a closed center neutral position to each of a pair of operating positions to communicate either of a pair of service passages with centrally disposed inlet means and the other service passage with outlet means through grooves in the valve spool and portions of the bore, characterized by: A. the outlet means being centrally located in the body, at one side of the bore; B. the service passages extending from the other side of the bore and intersecting the same at first zones which are spaced in axially opposite directions from the inlet means; C. a pair of U-shaped bridge passages in the body, each having opposite branches that intersect the bore at axially opposite sides of one of said first zones, and a bight at the same side of the bore as the outlet means; D. a U-shaped supply passage that embraces the inlet means and into which pressure fluid is caused to flow therefrom by the valve spool in either of its operating positions, said supply passage having opposite branches that intersect the bore at spaced locations axially inwardly from the bridge passages, and a bight at the side of the bore remote from the outlet means; E. a U-shaped return passage in the body, having opposite branches, one for each of said bridge passages, said return passage branches intersecting the bore at zones axially outwardly of the bridge passages and having a bight joining its branches and extending substantially lengthwise of the bore at the same side thereof as the outlet means but spaced farther from the bore than the outlet means and the bights of the bridge passages; F. a passageway communicating the bight of the return passage with the outlet means; and G. in its neutral position, the valve spool having

14. The closed center control valve of claim 13, wherein said inlet means intersects the bore intermediate the branches of the supply passage.

15. A hydraulic control valve having a body with a bore, and an elongated valve element shiftable in said bore to different positions to selectively communicate fluid flow passages in the body with one another, wherein said fluid flow passages provide: A. a pair of service passages that open from one side of the bore at first zones spaced apart lengthwise of the bore; B. a supply passage having a pair of branches, one for each service passage, and which branches open to the bore at second zones located axially inwardly of said first zones; C. a return passage having a pair of branches, one for each service passage, and which return branches open to the bore at third zones located axially outwardly of said first zones; D. inlet passage means providing for flow of supply fluid to the service passages via said supply passage under the control of the valve element, said inlet passage means intersecting the bore between the supply passage branches; and E. vent means intersecting the bore at zones axially inwardly of said first zones and cooperable with the valve element in the neutral position thereof to conduct leakage fluid from the inlet passage means to the return passage along a path wholly externally of the valve element.

16. The hydraulic control valve of claim 15, further characterized by: A. said service passages opening uninterruptedly to one side of the body from said bore; B. means on the valve element rendering said vent means operable only in the neutral position of the valve element; and C. means on the valve element operable in one position thereof to communicate said service passages with one another.

17. The hydraulic control valve of claim 16, wherein the valve element is operable to effect communication of the service passages with one another through the return passage.

18. A closed center control valve of the type having a body with a valve element which is operable to effect communication, through a chamber in which the valve element operates, of a service passage with either a pressure fluid supply passage or with an outlet passage in one or the other of a pair of operating positions to which the valve element is movable, characterized by: A. means on the valve element operable in a hold position thereof to close off the service passage from both the supply and the outlet passages, and to also close off the supply passage from the outlet passage; and B. vent passage means in the body