GB2151751A - Spool valve - Google Patents

Abstract

A spool valve 10 comprising a spool 11 of circular cross section mounted in a cylindrical bore, the ports 16-19 in the housing being separated by "O" rings 28 and the spool outer surface carrying slots 57 to straddle the "O" rings to interconnect the ports. The "O" rings are compressed through spacer rings which are subject to a variable resilient force. The slots 59 have shallow lead in portions and deeper centre ports. <IMAGE>

Description

SPECIFICATION Spool valve The present invention relates to a spool valve. Spool valves are valves in which a spool is movable to different positions, and in the different positions connects different inputs and outputs together.

Spool valves are well known and are frequently used to vary connections in a pneumatic system or hydraulic system. Spool valve assemblies normally comprises a spool which is usually of circular cross section mounted in a cylinder and the cylinder incorporates a plurality of ports connected to the hydraulic or pneumatic system and movement of the spool interconnects the ports in a predetermined way. In the arrangement to be described the spool is of a predetermined smaller diameter than the cylinder surface of the bore in which it is mounted and between the spool and the bore there are provided sealing "0" rings.

Interesting features of the spool valve assembly to be described are the manner in which ports are interconnected through slots in the surface of the spool itself and also the manner in which the "0" rings are tensioned so as to form a good seal between the bore and the spool.

A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is an axial section through a spool valve assembly according to the invention and, Figure 2 is a part axial section through the spool in a plane which includes a slot in the surface of the spool.

The spool valve assembly 10 comprises a spool 11 of circular cross section mounted axially in a bore 12 of cylindrical cross section within a housing 13 machined from solid metal. The housing 13 carries four ports 16,17,18,19whichextendtotheinner cylindrical surface of the bore 12 and to each of which is mounted a tube connector 21 to 24.

Around the spool 11 there are mounted five spaced "0" rings 25 to 29, the "0" rings 25 to 29 being spaced apart by spacer rings 31 to 34. Each end of the bore 12 includes a threaded portion 36,37 respectively, and respective threaded tube 39,40 are mounted to the threaded portions 36,37. Respective lock nuts 41,42 are also mounted on the threaded tubes 39,40 and abut against the end of the housing 13. Mounted axially beyond each end ofthe housing 13 are respective solenoids 43,44 which include respective movable cores 46,47 which are spring loaded by springs 48,49 so as to be retracted away from the spool 11.The movable cores 46,47 each include plungers 51,52 extending towards the spool 11. All of the parts thus far described are mounted on a suitable mounting frame 53.

The spool 11 also includes on its outer surface two slots 56, 57 (illustrated in Figures 1 and 2).

The apparatus thus far described is used as follows.

The spool valve assembly is adapted so that the spool 11 may be movable between a first and second position, in the first position illustrated in Figure 1 the ports 18,19 are interconnected and the ports 16, 17 are closed off. In a second position of the spool 11 to be described the ports 16 and 18 are interconnected and the ports 17 and 19 are interconnected.

Referring to Figure 1 in which the spool 11 is in the first position it will be noted that the slot 57 in the surface of the spool 11 extends across the plane of the "0" ring 27 and thus interconnects the ports 18 and 19.Thus air, gas or liquid can pass from port 18 to port 19 via the slot 57 or vice versa.

The port 16 is, however, sealed by means of the "0" rings 25,26 and the port 17 is sealed by means of the "0" rings 28,29.

If the solenoid 43 is energised the core 46 moves to the right in Figure 1 against the restoring action of the spring 48 and moves the spool 11 from the position shown in Figure 1 in which it is positioned as far as possible to the left to a second position in which it is moved as far as possible to the right.

In this second position the slot 56 straddles the "0" ring 26 and the slot 57 straddles the "0" ring 28. In this second position, therefore, the port 16 is interconnected with the port 18 and the port 17 is interconnected with the port 19 via the slots 56, 57 respectively.

The spool 11 may of course be moved back to the first position by energising the solenoid 45 which moves the core 47 to the left which in turn, via the plunger 52, pushes the spool 11 leftwards.

Referring to Figure 2 it will be seen that the use of slots, and in particular slots of the cross section shown in Figure 2, means that as the spool moves from the first to the second position then at a time when the slots 56,57 begin to straddle their respective "O" rings there is a very limited passage for fluid to pass through the slots and this means that if the assembly is being used to pass a gas or liquid the flow of gas or liquid initially through the slots 56,57 is restricted because of the small opening and there is a smooth build up of pressure rather than an abrupt change of pressure as with hitherto arrangements.To assist in this matter the slots 56,57 may include lead-in portions 58,59 which will gradually increase the cross-section available for gas or liquid to pass through the slots as the spool 11 is moved between its first and second positions. Of course, once the spool 11 is in either the first or second position, then the "0" ring will be straddled by the full depth of the slot 56 or 57 and will allow free passage of fluid or gas.

Furthermore, in past arrangements during assembly of the assembly 10 in manufacture it has been difficult to ensure that the "0" rings 25 to 29 seal with and bear with the correct pressure on the spool 11 and bore 12. The present arrangement provides a particularly convenient method of doing so.Thus during assembly the lock nuts 41 or 42 are disengaged from the end surface of the housing 13 and one or both of the threaded tubes 39,40 are screwed in on the threaded portions 36,37 so as to compress the "0" rings in the direction of the axis of the spool 11. The degree of compression can be preset by means of a torque measuring device rotating the tubes 39,40 so as to preload the "0" rings 25 to 29 in such a manner that they seal with the spool 11 and bore 12 with the correct degree of force. This force should be set so that movement of the spool 11 can be readily carried out by the relatively low power produced by the solenoids 43,44 and yet a suitable seal is provided.Once the threaded tubes 39,40 have been correctly located they can be retained in those positions by screwing the lock nuts 41,42 into engagement with the end bore of the housing 13 to retain the threaded tubes 39,40 in that position.

Such an arrangement considerably facilitates assembly of the apparatus.

The invention is particularly adapted for use with a differential pressure transducer, the two sides of differential pressure transducer being connected to the tube connectors 23, 24 respectively whereby in the first position the two sides of the pressure transducer are interconnected with one another so as to zero the apparatus and in the second position of the spool 11 the two sides of the pressure transducer are connected respectively to tube connectors 21,22.

In a preferred arrangement the depth of each slot 56,57 was conveniently arranged to be 0.6 mm and the width 0.6 mm.

The use of slots 56, 57 in the spool 11 maintains constant "0" ring compression which reduces pneumatic or hydraulic transients on the pressure measuring equipment and allows for smooth movement of the spool 11 between those two positions.

There has thus been described a bi-stable spool valve. However the invention is not restricted to the details of the foregoing example.

Claims (8)

1. A spool valve comprising: a spool of circular cross section including, on its cylindrical outer surface, an axially extending slot, so that at least one of its axial ends includes a lead in portion in which the depth of the slot gradually increases from a minimum at the end of the slot to a maximum towards the middle of the slot; a housing incorporating a cylindrical bore within which the spool is mounted and at least two ports which extend to the surface of the bore; ring seals mounted between the cylindrical bore and the spool to seal the cylindrical bore and spool with respect to one another, a ring seal being provided on each side of each port; and means to move the spool axially between a first position in which the slot straddles a ring seal between the two ports so as to interconnect the two ports and a secod position in which the slot does not straddle this ring seal and hence isolates the two ports, whereby as the spool moves from the second position to the first position the initial straddling of the ring seal is carried out by the lead in portion which thereby provides a gradually less restricting connection between the two ports.

2. A spool valve as claimed in claim 1 in which there are provided more than two ports.

3. A spool valve as claimed in claim 2 in which there is provided more than one slot.

4. A spool valve as claimed in claim 2 or 3 in which the or each slot incorporates a lead in at each axial end thereof.

5. A spool valve as claimed in any of claims 1 to 4 in which the ring seals comprise "0" rings.

6. A spool valve as claimed in claim 5 in which the "0" rings are held in position by means of spacer rings.

7. A spool valve as claimed in claim 6 in which the spacer rings are axially movable between the cylindrical bore and the spool and are held in position by variable resilient means to thereby submit the "0" rings to a variable compression.

8. Apparatus as claimed in claim 1 substantially as hereinbefore described with reference to the accompanying drawings.