GB2124737A - Spool valve - Google Patents

Abstract

A spool valve member (26) is slidable longitudinally within a bore 11, and has a first piston (28) at one end and a second piston (27) at the other end, the pistons being of equal size. High pressure fluid is continuously applied to a chamber 35 and against one face of the first piston 28, and low pressure is continuously applied chamber 34 and against the face of the second piston 27 which faces in the same direction as the face of the first piston to which high pressure is continuously applied. The other faces of the two pistons communicate with each other continuously, preferably through a passageway (40) in the valve body, with a control member, preferably in the form of a three-way valve (44), alternatively applying high or low pressure to these faces to move the spool valve member in one direction or the other, respectively. <IMAGE>

Description

SPECIFICATION Spool valve This invention reiates to spool valves, and more particularly to a four-way spool valve controlled by a solenoid-operated pilot valve.

In a four-way spool valve, a valve member in the form of a spool, i.e., two pistons joined by a rod, slides axially within an elongated bore in a valve body. The bore has a number of ports in its side wall which are typically connected to a source of pressurized fluid, a low pressure region, and a working device of some kind, respectively. The spool valve member has two extreme positions within the bore and controls communication between the ports. In one position of the valve member, the pressure port is connected to one of the working device ports and the exhaust port is connected to another of the working device ports.In the other position of the spool valve member, the working device portwhich was connected to the pressure port is connected to the exhaust port and the working device port which was connected to the exhaust port is connected to the pressure port.

Several types of pilot-operated spool valves are known. In one, a three-way pilot or control valve alternatively applies pressurized fluid or exhaust pressure to one side of a valve member piston. As the piston is pressurized, the spool valve member shifts in one direction, and as the piston is exhausted, a return spring shifts the valve member back to its original position.

In another type of valve, the two pistons of the spool are of different sizes. The smaller piston has high pressure fluid continuously applied to it. A three-way control valve alternatively applies pressurized fluid or exhaust pressure to the larger piston.

As the larger piston is pressurized, the spool valve member shifts in one direction, since with equal pressure applied to both pistons the force on the larger piston exceeds that on the smaller piston. As the larger piston is exhausted, the pressure on the smaller piston returns the valve member to its original position.

Still another type of spool valve employs a four-way pilot valve and two pistons of equal size.

The pilot valve pressurizes one piston and exhausts the other, to move the valve member in one direction, or alternatively pressurizes the other piston and exhausts the first, to move the valve member in the other direction. In another version of this type of valve, a single piston is used and its opposite faces alternatively pressurized and exhausted.

Each of these known types of valves has advantages and drawbacks. The valve using a three-way control valve and a return spring is inexpensive to produce. However, the spring eventually fails due to fatigue, as a result of which the valve fails. Furthermore, the constant force exerted by the spring makes use of the valve impractical at very low pressures.

A valve employing different size pistons avoids use of a spring, but is more expensive to make, since the overall size of the valve must be larger to accommodate the larger piston. To avoid using a larger size piston, two identical pistons in tandem can be used in place of the larger piston. However, this approach adds the expense of an additional piston, piston seals, and a vent between the tandemly arranged pistons.

Use of a four-way control valve also avoids use of a spring and permits two pistons of equal size to be employed. However, it is more expensive to manufacture due to the complexity of the pilot valve and its associated circuit.

It is an object of the present invention to provide a spool valve incorporating a valve member having two pistons of equal size, which has no need for a return spring, and is operable by a three-way pilot valve. The valve of this invention, therefore, has all the advantages of the known valves described above, and none of the disadvantages.

Afeature of the invention involves continuously pressurizing the face of one piston which faces in a particular direction and continuously exhausting the face of the other piston which faces in the same direction, and using the control valve to pressurize the other faces of both pistons, to move the valve member in one direction, or alternatively exhaust the other faces of both pistons, to move the valve member in the other direction.

It is another object of the invention to provide such a spool valve wherein each piston is furnished with a one-way seal, and neither seal is continuously loaded.

Additional objects and features of the invention will be apparent from the following description in which reference is made to the accompanying drawings.

In the drawings: Figure 1 is a schematic longitudinal crosssectional view of a spool valve according to the present invention, the valve member being in one of its extreme positions; and Figure 2 is a view similar to Figure 1, the valve member being in the other of its extreme positions.

The spool valve chosen to illustrate the present invention includes a valve body 10 having elongated bore 11. Bore 11 is closed at one end by an end plate 12 and atthe other end byan end plate 13, the end plates being mounted on body 10 in a fluid-tight manner by suitable fasteners (not shown). Body 10 is formed, in this example, with six ports 14, 15, 16, 17, 18 and 19 in the side wall of bore 11. Projecting into bore 11 are six annular seals 20, 21 and 22, formed for example of rubber or plastic, one seal being located between each two successive ports, and seal 22 being arranged beyond port 17.

Seals 20, 21 and 22 are maintained separated by spacers (not shown), and the assembly of seals and spacers is maintained in place within bore 11 bytwo snap rings 23 accommodated by two annular recesses in the wall of bore 11.

Port 18 in body 10 is adapted for connection to a source of pressurized fluid, such as compressed air, and ports 14, 17 and 19 connect with a low pressure region, such as the atmosphere, where the fluid whose flow is being controlled is air, or a reservoir, where the fluid is a liquid. Ports 15 and 16 are connectable to a working device being controlled by the spool valve, such as the opposite sides of a piston within a cylinder (not shown).

A spool valve member 26, arranged to slide axially within bore 11 may include two pistons 27 and 28 of equal diameter joined by a rod 29. Pistons 27 and 28 fit snugly but slideably within bore 11, and rod 29 fits snugly but slidably within seals 20-22, the engagement between the rod and seals being fluid tight.

Rod 29 has two reduced diameter regions 30 spaced radially inward of seals 20-22. Valve member 26 is movable between two extreme positions shown respectively in Figures 1 and 2. In the position shown in Figure 1, pressure port 18 communicates with working device port 16 through bore 11, and exhaust port 14 communicates with working device port 15 through bore 11. When valve member 26 moves to the Figure 2 position, pressure port 18 communicates with working device port 15, and exhaust port 17 communicates with working device port 16.

Piston 27 defines, together with end plate 12, a chamber 33 within bore 11, and the same piston defines, together with seal 20, an annular chamber 34 within bore 11. Similarly, piston 28 defines, together with end plate 13, a chamber 35, and the same piston defines, together with seal 22, an annular chamber 36. A longitudinal passageway 37 in body 10 is in constant communication with pressure port 18 via a short branch passageway 38 and bore 11. At one of its ends, passageway 37 joins a passageway 39 in end plate 13 which extends between passageway 37 and chamber 35. Thus, pressure port 18 is in continuous communication with chamber 35 in all positions of valve member 26, through bore 11 and passageways 38, 37 and 39.

Chamber 34 continuously communicates with a low pressure region (atmosphere or reservoir), in all positions of valve member 26, through vent port 19.

It will be seen, therefore, that one face of piston 28, i.e., the rightward facing one in the drawings, has high pressure continuously applied to it, and the face of piston 27 which faces in the same direction as that face of piston 28 has low pressure continuously applied to it. A longitudinal passageway 40 extends from chamber 36 to a passageway 41 in end plate 12 which in turn extends to chamber 33, thereby providing continuous communication between chambers 33 and 36 in all positions of valve member 26.

Movement of spool valve member 26 is controlled by a three-way solenoid operated pilot valve 44, mounted on spool valve body 10 in a fluid-tight manner. The body of valve 44 is formed with an internal bore 45 having three ports 46,47 and 48.

Port 46 communicates constantly with passageway 37 and hence with pressure port 18; port 47 com municates constantly with the low pressure region (atmosphere or reservoir); port 48 provides, together with a passageway 49 in body 10 and a passageway 50 in end plate 12, constantcommuni- cation between bore 45 and chamber 33.

Movable axially within bore 45 is a pilot valve member, or armature 53, the movement of which is controlled by an electrical solenoid 54. When the solenoid is deenergized (Figure 1), armature 53 is held in its lowermost position by a spring (not shown) wherein it closes port 46 and opens port 47.

As a result, chamber 33 is exhausted through passageways 50,49, and 48, bore 45, and vent port 47. When solenoid 54 is energized, armature 53 moves to its uppermost position (Figure 2) wherein it closes port 47 and opens port 46. As a result, chamber 33 is pressurized from pressure port 18 through bore 11, passageways 38 and 37, port 46, bore 45, port 48, and passageways 49 and 50. Upon deenergization of the solenoid, the spring returnsarmature 53 to its lowermost position (Figure 1).

In operation, when solenoid 54 is deenergized, low pressure exists in chambers 33 and 36, because chamber 36 is in constant communication with chamber 33, and the iatter chamber communicates with vent port 47 of pilot valve 44. The same low pressure, as always, exists in chamber 34, but high pressure from port 18 is present, as always, in chamber 35. Thus, the low pressures on both sides of piston 27 are balanced, but the imbalance of pressures on the opposite sides of piston 28 result in a net force which moves valve member 26 toward the left to its extreme position shown in Figure 1.

When solenoid 54 is energized, high pressure fluid is introduced into chambers 33 and 36, because these chambers are connected to pressure port 18 through pilot valve port 46. Low pressure continues to exist in chamber 34 and high pressure in chamber 35. The high pressures on both sides of piston 28 are balanced, but the imbalance of pressures on the opposite sides of piston 27 result in a net force which moves valve member 26 toward the right to its extreme position shown in Figure 2.

Pistons 27 and 28 are furnished with annular seals 55 and 56, respectively, each seal being located between the mutually slidable piston wall and the wall of bore 11. Seals 55 and 56 are cup-shaped seals having a U-shaped cross-section. Seal 55 is arranged so that the open side of its U-shape faces chamber 33, and seal 56 is arranged so that the open side of its U-shape faces chamber 35. Because of its shape, each seal operates uni-directionally. Seai 55 prevents leakage of fluid from chamber 33 to chamber 34, but not vice versa, and seal 56 prevents leakage of fluid from chamber 35 to chamber 36, but not vice-versa. It will be appreciated that seal 56 is loaded, i.e., serving to prevent fluid leakage, when the spool valve is in its Figure 1 condition, but in this condition seal 55 is unloaded, i.e., there is no pressure differential across it. When the valve is in its Figure 2 condition, sea 56 is unloaded and seal 55 is loaded. Thus, since each seal is loaded only part of the time that the spool valve is in operation, seal life is extended beyond that of a valve configuration in which the seals are constantly loaded. The reason is that a constantly loaded seal will deform and wear, and hence lose its sealing ability, sooner than an intermittently loaded seal.

Although spool valve member 26 has been de scribed as comprising pistons 27 and 28 joined by rod 29, the two pistons and the rod can be three unattached elements. In the claims which follow, the term "spool valve member" is intended to refer to pistons 27 and 28 and a rod between them, whether or not the three are physically joined to each other.

The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended

Claims (9)

claims. CLAIMS

1. Aspool valve comprising: a valve body having an elongated bore and a plurality of ports in the body along the length of the bore, one of the ports being a pressure port connectable to a source of pressurized fluid, a spool valve member slidable longitudinally within the bore between two extreme positions for controlling fluid flow between the ports, the spool valve member having a first piston at one of its ends and a second piston at the other of its ends, means for continuously applying high fluid pressurn to one face of the first piston, means for continuously applying low fluid pressure to one face of the second piston which faces in the same direction as said one face of the first piston, and control means for (I) simultaneously applying high pressure fluid to the other face of each of the first and second pistons to move the spool valve member to one of its extreme positions, or alternatively (II) simultaneously applying low pressure to the other face of each of the first and second pistons to move the spool valve member to its other extreme position.

2. A spool valve as defined in Claim 1 including a chamber adjacent to each face of each piston, and wherein the means for constantly applying high fluid pressure to the first piston includes a passageway providing constant communication between the pressure port and the chamber adjacent to said one face of the first piston.

3. A spool valve as defined in Claim 2, wherein the control means controls fluid flow between the pressure port and the chamber adjacent to said other face of the second piston, and including a passageway providing constant communication between the chamber adjacent to said other face of the second piston and the chamber adjacent to said other face of the first piston.

4. A spool valve as defined in Claim 3, wherein the control means includes a control valve having a port communicating with a low pressure region, a port communicating with said pressure port, and a third port communicating with the chamber adjacent to said other face of the second piston, the control valve alternatively providing communication between the third port and the low pressure region or the third port and the pressure port.

5. A spool valve as defined in Claim 4, wherein the control valve is a three-way valve having an armature responsive to energization of an electrical solenoid.

6. A spool valve as defined in Claim 3, wherein said passageways are located within the valve body.

7. A spool valve as defined in Claim 1, wherein the first and second pistons are of equal size.

8. A spool valve as defined in Claim 1, including an annular seal between each piston and the wall of the bore within which it moves, each seal being a one-way seal which prevents fluid flow from the chamber adjacent to the longitudinal outer face of the piston toward its longitudinal inner face, and wherein said one face of this first piston is its longitudinal outer face and said one face of the second piston is its longitudinal inner face.

9. A spool valve substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.