US3618636A

US3618636A - Pneumatic logic valve

Info

Publication number: US3618636A
Authority: US
Inventors: Charles J Grimland; Peter C Huff
Original assignee: Dynamco Inc
Current assignee: Dynamco Inc
Priority date: 1969-03-26
Filing date: 1969-03-26
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09

Abstract

A pneumatic logic valve including a cylinder that is closed by end caps and a valve spool mounted in the cylinder for movement between the end caps. The spool is driven by compressed air that enters the cylinder through passageways in the end caps. Reduced diameter sections of the spool interconnect different pairs of logic holes depending on the position of the spool in the cylinder. Accessories mounted in the cylinder in place of the end caps equip the valve for visible spool position indication, spring-driven spool return and low-pressure signal spool actuation.

Description

United States Patent 721 Inventors CharlesLGrimland [2 l Appl. No. [22'] Filed [45] Patented 73] Assignee Garland;

Peter C. l-lufl, Dallas, both of Tex. 810,746

Mar. 26, 1969 Nov. 9, 1971 Dynameo Inc.

Dallas, Tex.

[54] PNEUMATIC LOGIC VALVE 8 Claims, 5 Drawing Figs. [52] US. Cl. l37/625.6, 137/556 [51] Int. Cl. F1611 11/07 [50] Field Search 137/269,

[56] References Cited UNITED STATES PATENTS 2,985,469 5/1961 Bowman 285/304 X 2,584,890 2/1952 Leonard 251/634 X 2,648,346 8/1953 Deardorfiet al. 251/62 X 2,773,486 12/1956 Alberg 137/625.63

2,973,746 3/1961 Jupa l37/625.63 3,323,547 6/1967 Van l-lusen et al l37/625.64 3,329,159 7/1967 Herion l37/625.63 X 3,401,711 9/1968 Kubilos 137/625.63 X 3,470,910 1 /1969 Loveless... 137/6256 3,473,547 10/1969 Coakley 137/625.63 X 3,474,828 10/1969 Wheeler et a1 137/6256 FOREIGN PATENTS 1,487,472 7/1967 France 137/625.64

740,225 11/1955 Great Britain 137/625.64

Primary Examiner-M. Cary Nelson Assistant Examiner-Richard Rothman Auorney- Richards, Harris 81 Hubbard ABSTRACT: A pneumatic logic valve including a cylinder that is closed by end caps and a valve spool mounted in the cylinder for movement between the end caps. The spool is driven by compressed air that enters the cylinder through passageways in the end caps. Reduced diameter sections of the spool interconnect different pairs of logic holes depending on the position of the spool in the cylinder. Accessories mounted in the cylinder in place of the end caps equip the valve for visible spool position indication, spring-driven spool return and low-pressure signal spool actuation.

PATENTED RUV 9 I97! FIG. I

FIG. 2

INVENTOR3: CHARLES 'J, GRIMLAND PETER c. HUFF 44 MAW /l //yI//// ATTORNEYS PNEUMATIC LOGIC VALVE BACKGROUND OF THE INVENTION The art of logic control is divided into two distinct branches, electrical and fluid. The electrical branch employs electricity as a working medium and includes both relay networks and purely electronic systems. In the fluid branch the working medium is usually a compressed gas, such as air. The fluid branch includes both fluidic systems, which in the pure form employ no moving parts but rather operate directly on moving fluid streams, and pneumatic systems in which valves and other mechanical devices are used to control fluid flow.

I-Ieretofore, the development of pneumatic logic control systems has been hampered by the high cost and large size of the logic elements available for use in such systems. This invention relates to a pneumatic logic valve that is very small in size and very inexpensive to manufacture when compared with the valves presently available. Also, the invention includes several accessories suitable for use with the basic valve.

SUMMARY OF THE INVENTION In the preferred embodiment, this invention comprises a valve body having a bore formed in it and a hole extending through it, at least one end member for closing the bore and a disc-shaped valving member mounted in the bore for movement from one side of the hole to the other. Preferably, the end member includes a locating surface for limiting the travel of the valving member in one direction.

DESCRIPTION OF THE DRAWINGS A more complete understanding of the invention may be had by referring to the following detailed description when taken in conjunction with the drawings, wherein:

FIG. 1 is a top view of a pneumatic logic valve employing the invention;

FIG. 2 is a sectional view taken generally along the line 2-2 in FIG. I in the direction of the arrows;

FIG. 3 is a sectional view taken generally along the line 3-3 in FIG. I in the direction of the arrows;

FIG. 4 is a front view of the device shown in FIG. I in which certain parts have been broken away more clearly to illustrate a first accessory suitable for use with the device shown in FIG. I, and

FIG. 5 is a front view of the device in FIG. I in which certain parts have been broken away more clearly to illustrate second and third accessories suitable for use with the device shown in FIG. 1.

DETAILED DESCRIPTION Referring now to the drawings, like reference numerals designate like parts throughout the several views. Referring particularly to FIG. 2, there is shown a pneumatic logic valve employing the invention and including a valve body 12 The body 12 is secured to a mounting base 14 by a pair of body screws 16, only one of which is shown in FIG. 2. A onepiece gasket 18 is positioned between the body 12 and the mounting base 14. As is best shown in FIG. 1, the screws 16 extend into holes 20 formed in the mounting base 14. The entire pneumatic logic valve 10 may be mounted by suitable fasteners extending through a pair of holes 22 formed in the base 14.

Referring to FIGS. 2 and 3, the body 12 has a cavity 24 extending axially through it. The cavity 24 includes a reduced central section 26 which is circular in left-hand and a pair of enlarged end sections 28. The body 12 also has a plurality of radially extending holes 30 formed in it. Each of the holes 30 extends outwardly from the central section 26 of the cavity 24 into communication with a hole 32 formed in the gasket 18. The holes 32 each extend to a hole 34 formed in the mounting base 14 which in turn extends to a high pressure barb 36 mounted in the mounting base 14.

The barbs 36 serve to connect the pneumatic logic valve 10 to flexible tubes (not shown) which in turn extend to compressed air emitting and receiving devices. In use, the left hand and right-hand barbs 36 shown in FIGS. 1 and 2 are normally utilized as pilot or control ports for the valve 10 while the five centermost barbs 36 are utilized as logic ports. That is, the operation of the valve 10 is nonnally controlled by use of the left-hand and right-hand barbs 36 while interconnection of the five center barbs 36 is controlled by the valve 10.

The cavity 24 of the body 12 is closed by a pair of end caps 38 positioned in the end sections 28 and extending into the central section 26 of the cavity 24. The end caps 38 are retained in the end sections 28 by a pair of end plates 40 which are in turn each secured to the body 12 by a pair of end cap screws 42, only two of which are shown in FIG. 2. The end caps 38 each have a pair of

annular grooves

44 and 46 formed in them. The grooves 44 receive and position a pair of O-rings 48 which serve to seal the interior of the cavity 24. The grooves 46 serve to interconnect the outermost radially extending holes 30 in the body 12 with the center section 26 of the cavity 24. The end caps 38 also have accurately located end surfaces 50 which serve as reference surfaces to define the working length of the cavity 24.

The pneumatic logic valve 10 further includes a valve spool 52 mounted in the cavity 24 for axial movement with respect to the body I2. The spool 52 includes four valving portions 54 each having an outside diameter equal to the diameter of the central section 26 of the cavity 24 and three reduced portions 56 each positioned between a pair of the valving portions 54. The valving portions 54 of the spool 52 have an axial length equal to the diameter of the holes 30 while the reduced portions 56 have an axial length equal to three times the diameter of the holes 30. The working length of the cavity 24 defined by the surfaces 50 of the end caps 38 exceeds the overall axial length of the spool 52 by a distance equal to twice the diameter of the holes 30. Thus, the stroke of the spool 52 in the cavity 24 is equal to twice the diameter of the holes 30.

In operation, the positioning of the spool 52 in the cavity 24 is controlled by the relative pressures that are supplied to the pneumatic logic valve 10 through the left-hand and right-hand high-pressure barbs 36. The spool 52 is moved to the position shown in full lines in the drawing whenever the pressure applied to the valve 10 through the right-hand barb 36 exceeds the pressure applied through the left-hand barb 36. The spool 52 is moved to the dash line position shown in FIG. 2 whenever the pressure applied to the valve 10 through the left-hand barb 36 exceeds the pressure applied through the right-hand barb 36.

The spool 52 serves to interconnect various ones of the center barbs 36 depending on whether it is in the full line position or the dash line position as shown in FIG. 2. When the spool 52 is in the full line position the barbs 36 indicated by the

numerals

2 and 5 in FIG. 1 are interconnected by the righthand reduced portion 56 of the spool 52, the barbs 36 indicated by the numerals I and 4 in FIG. I are interconnected by the center reduced portion of 56 of the spool 52 and the barb 36 indicated by the numeral 3 in FIG. 1 is blocked. When the spool 52 is in its dash line position the barbs 36 indicated by the numerals I and 3 in FIG. I are interconnected by the left-hand reduced portion 56 of the spool 52, the barbs 36 indicated by the numerals 4 and 2 in FIG. 1 are interconnected by the center reduced portion 56 of the spool 52 and the barbs 36 indicated by the numeral 5 in FIG. I is blocked. Thus, the pressures applied to the spool 52 through the endmost barbs 36 serves to control the interconnection of the live center barbs 36.

The pneumatic logic valve construction shown in the the body 12 into the cavity 24. The spool 52 may be formed from ordinary round stock by turning the reduced positions 56 and grinding the outer diameter of the valving portions 54. Thus, the entire valve 10 is formed by straightforward and inexpensive machining operations without the necessity of providing elaborate castiny and complicated manufacturing operations. The resulting valve is very small in size when compared with prior logic valve designs. For example, the body I2 typically has outside dimension of 1% inches inches x inches.

While the pneumatic logic valve 10 may be formed from any convenient material, it is important that the component parts of the valve be both corrosion and wear resistant. Furthermore, it is important that the spool and the body of the valve have similar coefficients of temperature expansion so that the entire valve is afi'ccted uniformly by temperature. To meet these requirements it has been found convenient to form the spool 52 from stainless steel and to form the body 12 from free machining steel. After machining, the body 12 is coated with electroless nickel which is then heat treated for hardness. The use of these materials results in a valve which has all of the required characteristics and yet is inexpensive to manufacture.

In addition to low cost and small size, the valve shown in the drawing has many advantages over prior designs, many of which result from the use of the end caps 38. First, the end caps 38 extend well into the center section 26 of the cavity 24 formed in the body l2. That is, the working length of cavity 24 as defined by the surfaces 50 of the end caps 38 is considerably shorter than the total length of the center section 26. It is well known that imperfections resulting from the manufacture of a cylindrical cavity are frequently more pronounced at the ends of the cavity than at the center. The positioning of the surfaces 50 well into the interior of the center section 26 of the cavity 24 renders minor defects in the ends of the center section 26 irrelevant to the operation of the valve 10.

Second, the grooves 66 which interconnect the outermost radially extending holes 30 in the body l2 with the center section 26 provide a "no volume" pilot cavity for the valve 10. That is, only the small volume of the grooves 46 need be filled before the full pressure of the compressed air is applied against the spool 52. Also, the grooves 66 provide a place for the accumulation of any refuse that is driven to the ends of the cavity 26 by the spool 52. This is very important because, if the grooves 46 were not provided, such refuse might build up against the surfaces 50 and thereafter impede the travel of the spool 52 in the cavity 24.

Finally, the O-rings Alb have a spring effect which tends to drive the end caps 38 out of the cavity 24. Because of the spring effect of the O-rings 48, the working length of the cavities 26 is easily controlled by simply controlling the length of the end caps 38 and the overall length of the body 12. The rings 48 drive the end caps 38 against the end plates 40 which function to simply maintain the ends of the end caps 38 in alignment with the ends of the body 12. By this means, the surfaces 50 are accurately positioned without the use of any locating surface whatsoever formed in the interior of the cavity 24.

2 now to FIG. 4, there is shown a first accessory 60 for the device shown in FIGS. l, 2 and 3 which provides a visual indication of the position of the spool 52 of the pneumatic logic valve 10. The accessory 60 includes an end cap 62 which replaces a nonnal end cap 38 and which is similar to the end caps 38 in that it is provided with an annular groove 63 which receives and positions an O-ring 64 and an annular groove 65 positioned in alignment with the leftmost hole 30 in the block 12. The end cap 62 differs from the end caps 38 in that it has a small hole 66 extending axially through it. A transparent block 67 having a blind hole 68 extending into it is used in the accessory 60 in place of a conventional end plate 40. A gasket 69 is positioned between the block 67 and the body 12. The gasket 69 and the block 67 are secured to the body 12 of the valve by a pair of screws 70, only one of which is shown. The accessory 6b is completed by a pin 72 which extends from the spool 52 of the valve W and which extends through the hole 66 in the end cap 62. The pin 72 has a layer of colored material 74 extending around its distal end. The layer 74 is moved into and out of the hole 66 by the spool $2 so that the pin 72 is visible through the block 67 whenever the spool 52 is positioned as shown in full lines in FIG. 2 and is not visible through the block 67 whenever the spool 52 is positioned as shown in dash lines in FIG. 2.

Referring now to PEG. 5, a second accessory 76 for the device shown in FIGS. l, 2 and 3 is illustrated. The accessory 76 includes an elongate body 78 which is positioned in the cavity 24 in the body 12 of the valve 10 in place of a normal end cap 33. The body 73 is retained by a plate 80 which extends around the body 72 and which is secured by a pair of screws 81, only one of which is shown. A compression spring 82 is positioned within the body 76 and serves to urge the spool 52 of the pneumatic logic valve 16 to the left as shown in FIG. 5. A groove @3 formed in the body 76 interconnects the right-hand hole 30 formed through the body 12 and the cavity so that whenever the accessory 76 is used, the spring 32 overcomes the effect of equal pressures applied to both ends of the spool 52. The body 78 has an end surface 84 formed on it which limits rightward movement of the spool 52 and has a shoulder 85 formed around it which positions an O-ring in sealing engagement with the body I2. 12.

Also shown in FIG. 5 is a third accessory 87 which may be used to interface the pneumatic logic valve 10 with a fluidic logic circuit or with any other source of low-pressure control signals. The accessory 87 includes a body 88 which is positioned in the cavity 24 of the body 12 in place of a normal end cap 38. The body 88 includes an annular passageway 89 positioned in alignment with the leftmost hole 30 in the block 12 and an annular groove 90 which receives and positions an 0- ring 91. An elongate hole 92 extends axially through the body 38 and a pair of radially extending slots 94 extend from the annular passageway 90 to the axial hole 92.

The axial hole 92 extends to a conically shaped cavity 96 formed in the body 88 which in turn extends to a disc-shaped cavity 98 formed therein. The disc shaped cavity extends to a pair of outlet ports 106 which normally serve to vent the passageway 90 to the atmosphere. A ball 1102 is positioned in the conically shaped cavity 96 and a free floating disc 104 is positioned in the disc shaped cavity 96. A hole 106 extends through the body 88 from the disc-shaped cavity 98 to a source of low-pressure control signals (not shown), such as a fluidic system, etc.

In operation, compressed air is continuously supplied through the left-handmost barb 36 of the valve to the lefthandmost hole 30 formed in the body 12. A liner 108 positioned in the left-handmost hole 30 serves as an orifice to reduce the efi'ective pressure applied through the left-handmost barb 36. Air flowing through the liner 108 passes through the annular passageway 90, the radially extending slots 94 and the axially extending hole 92 to the conically shaped cavity 96. From the conically shaped cavity 96, the air passes through the disc-shaped cavity 98 and out the outlet ports 100.

Whenever a signal is applied through the hole 106, the disc 104 is driven to the right as shown in FIG. 5. This causes the ball 102 to engage the walls of the conically shaped cavity 96 thereby closing the end of the axially extending hole 92. Air entering the valve 30 through the left-handmost hole 30 quickly increases the pressure in the interior of the cavity 24. When the pressure reaches a predetermined level, the spool 52 is driven to the right against the action of the spring 82 of the accessory 76.

Of course, the accessory 87 can be used without the accessory 76, if desired. The accessory 87 serves to amplify signals entering the hole 106 as much as I06 times. That is, signals having pressures as much as 206 times less than the pressure necessary to drive the spool 52 to the right against the action of the spring 83 can be used to control the spool 52 by means of the accessory 87.

Of course, the pneumatic logic valve shown in the drawings can be used with or without the accessories shown in FIG. 4 and 5, as desired. Also, many other accessories can be used with the valve shown. it should be understood that although only one embodiment of the valve and only three accessories therefore are shown in the drawings and described in the foregoing specification, the invention is not limited to the embodiment and accessories shown but is capable of rearrangement, modification and substitution of parts and elements without departing from the spirit of the invention.

What is claimed is:

l. A pneumatic logic valve including:

an outer valve housing having a cylindrical cavity formed in it that is circular in shape and of uniform diameter throughout its length and having at least two holes of substantially equal diameter extending through it into communication with the cavity, said holes being of uniform diameter throughout their lengths and having axes which are separated axially of the cavity by a distance substantially equal to twice the diameter of the holes;

a valve spool mounted in the cavity and comprising a pair of circular valving portions each equal in diameter to the diameter of the cavity and at least one having a length substantially equal to the diameter of the holes and a reduced diameter portion extending between the valving portions and having a length substantially equal to three times the diameter of the holes;

means for moving the spool axially in the cavity between points separated by a distance substantially equal to twice the diameter of the holes and thereby selectively interconnecting the holes through the reduced diameter portion of the spool;

an end cap positioned in one end of the cavity and a compression spring mounted in the end cap and extending therefrom into engagement with the valve spool for urging the valve spool toward one of the points in the cavity; and

signal amplifier means positioned in the other end of the cavity for urging the valve spool toward the other point in the cavity and comprising a conically shaped passageway, a disc-shaped passageway extending from the conically shaped passageway, and a diaphragm positioned in the disc-shaped passageway.

2. The pneumatic logic valve according to claim I further including additional circular holes having diameters substantially equal to the diameter of the two holes and extending through the valve body into communication with the cavity, said additional holes having axes which are separated axially of the cavity by a distance substantially equal to twice the diameter of the holes, an additional circular valving portion on the valve spool having a diameter substantially equal to the diameter of the cavity, and an additional reduced diameter portion on the valve spool having a length substantially equal to three times the diameter of the holes.

3. A pneumatic logic valve comprising:

an outer valve housing having a right circular cylindrical cavity formed through it which is of uniform diameter throughout its length and having a plurality of holes formed in it which extends into communication with the cavity, said holes having equal, uniform diameters throughout their lengths and being separated by center to center distances axially of the cavity equal to twice their diameters and extending to a substantially flat surface on the valve housing.

a valve spool mounted in the cavity and comprising circular valving portions having diameters equal to the diameter of the cavity and having lengths equal to the diameters of the holes, said valving portions being separated by a reduced diameter portion having a length equal to three times the diameter of the holes;

means for moving the valve spool in opposite directions within the cavity and thereby alternately interconnecting predetermined pairs of the holes through the reduced diameter gortion of the valve spool; a pair of en caps mounted in the opposite ends of the cavity for limiting the movement of the valve spool axially therein;

means positioned between outwardly facing surfaces on the valve housing and inwardly facing surfaces on the end caps for sealing the cavity and for biasing the end caps to move outwardly from the cavity;

means mounted on the ends of the valve housing for limiting the outward movement of the end caps under the action of the sealing and biasing means and thereby defining the limits of movement of the valve spool within the cavity;

a substantially fiat gasket mounted on the surface of the housing and having holes extending through it into communication with the holes in the housing, and

a base mounted on the gasket and having holes extending through it into communication with the holes in the gasket.

4. The pneumatic logic valve according to claim 3 further including a plurality of tube receiving barbs each mounted on the base and each having a hole extending through it into communication with one of the holes in the base.

5. The pneumatic logic valve according to claim 4 wherein the end caps include portions of lesser diameter than the cavi ty which extend into the cavity for engagement by the spool, and wherein the spool-moving means comprises passageways formed in the body for directing air into the portions of the cavity surrounding the end caps.

6. A pneumatic logic valve comprising:

a valve body having a circular cavity fonned through it which is of uniform diameter throughout its length and having a plurality of holes extending through it into communication with the cavity, said holes being of uniform diameter throughout their lengths and extending to a substantially flat surface on the valve body;

a valve spool mounted within the cavity and comprising a pair of circular valving portions having the same diameter as the cavity and a reduced diameter portion extending between the valving portions;

means for moving the valve spool in opposite directions axially of the cavity and thereby selectively interconnecting predetermined pairs of the holes in the valve body through the reduced diameter portion of the valve spool;

a substantially flat gasket mounted on the fiat surface of the valve body and having a plurality of holes formed through it each individual to and extending into communication with one of the holes in the valve body; and

a base for receiving the gasket and having a plurality of holes formed in it each individual to and extending into communication with one of the holes in the gasket.

7. The pneumatic logic valve according to claim 6 further including a pair of end caps positioned in the opposite ends of the circular cavity, a pair of O-rings each positioned between an outwardly facing surface on the valve body and an inwardly facing surface on one of the end caps for sealing the cavity and for urging the end caps to move outwardly from the cavity, and means mounted on the ends of the valve body for locating the end caps against the action of the O-rings.

8. The pneumatic logic valve according to claim 7 including portions smaller in diameter than the cavity which extend into the cavity, and wherein the spool moving means comprises means for directing air into the portions of the cavity adjacent the end caps.

Claims

1. A pneumatic logic valve including: an outer valve housing having a cylindrical cavity formed in it that is circular in shape and of uniform diameter throughout its length and having at least two holes of substantially equal diameter extending through it into communication with the cavity, said holes being of uniform diameter throughout their lengths and having axes which are separated axially of the cavity by a distance substantially equal to twice the diameter of the holes; a valve spool mounted in the cavity and comprising a pair of circular valving portions each equal in diameter to the diameter of the cavity and at least one having a length substantially equal to the diameter of the holes and a reduced diameter portion extending between the valving portions and having a length substantially equal to three times the diameter of the holes; means for moving the spool axially in the cavity between points separated by a distance substantially equal to twice the diameter of the holes and thereby selectively interconnecting the holes through the reduced diameter portion of the spool; an end cap positioned in one end of the cavity and a compression spring mounted in the end cap and extending therefrom into engagement with the valVe spool for urging the valve spool toward one of the points in the cavity; and signal amplifier means positioned in the other end of the cavity for urging the valve spool toward the other point in the cavity and comprising a conically shaped passageway, a disc shaped passageway extending from the conically shaped passageway, and a diaphram positioned in the disc shaped passageway.

2. The pneumatic logic valve according to claim 1 further including additional circular holes having diameters substantially equal to the diameter of the two holes and extending through the valve body into communication with the cavity, said additional holes having axes which are separated axially of the cavity by a distance substantially equal to twice the diameter of the holes, an additional circular valving portion on the valve spool having a diameter substantially equal to the diameter of the cavity, and an additional reduced diameter portion on the valve spool having a length substantially equal to three times the diameter of the holes.

3. A pneumatic logic valve comprising: an outer valve housing having a right circular cylindrical cavity formed through it which is of uniform diameter throughout its length and having a plurality of holes formed in it which extend into communication with the cavity, said holes having equal, uniform diameters throughout their lengths and being separated by center to center distances axially of the cavity equal to twice their diameters and extending to a substantially flat surface on the valve housing; a valve spool mounted in the cavity and comprising circular valving portions having diameters equal to the diameter of the cavity and having lengths equal to the diameters of the holes, said valving portions being separated by a reduced diameter portion having a length equal to three times the diameter of the holes; means for moving the valve spool in opposite directions within the cavity and thereby alternately interconnecting predetermined pairs of the holes through the reduced diameter portion of the valve spool; a pair of end caps mounted in the opposite ends of the cavity for limiting the movement of the valve spool axially therein; means positioned between outwardly facing surfaces on the valve housing and inwardly facing surfaces on the end caps for sealing the cavity and for biasing the end caps to move outwardly from the cavity; means mounted on the ends of the valve housing for limiting the outward movement of the end caps under the action of the sealing and biasing means and thereby defining the limits of movement of the valve spool within the cavity; a substantially flat gasket mounted on the surface of the housing and having holes extending through it into communication with the holes in the housing, and a base mounted on the gasket and having holes extending through it into communication with the holes in the gasket.

5. The pneumatic logic valve according to claim 4 wherein the end caps include portions of lesser diameter than the cavity which extend into the cavity for engagement by the spool, and wherein the spool moving means comprises passageways formed in the body for directing air into the portions of the cavity surrounding the end caps.

6. A pneumatic logic valve comprising: a valve body having a circular cavity formed through it which is of uniform diameter throughout its length and having a plurality of holes extending through it into communication with the cavity, said holes being of uniform diameter throughout their lengths and extending to a substantially flat surface on the valve body; a valve spool mounted within the cavity and comprising a pair of circular valving portions having the same diameter as the cavity and a reduced diameter poRtion extending between the valving portions; means for moving the valve spool in opposite directions axially of the cavity and thereby selectively interconnecting predetermined pairs of the holes in the valve body through the reduced diameter portion of the valve spool; a substantially flat gasket mounted on the flat surface of the valve body and having a plurality of holes formed through it each individual to and extending into communication with one of the holes in the valve body; and a base for receiving the gasket and having a plurality of holes formed in it each individual to and extending into communication with one of the holes in the gasket.