GB2204664A - Spool valves - Google Patents

Abstract

A spool valve comprises a housing (3), a cylindrical chamber (6) and a number of ports (5) spaced along the chamber (6) for the inlet and outlet of fluid. A spool (4) is reciprocatable along the chamber (6). O ring seals (7) are retained in sealing contact with the housing (3) and spool (4) in annular grooves (8) and the spool (4) includes passage means (9), which comprise diagonal through passages 14 or axially extending grooves (100). The grooves (100) are circumferentially spaced around the spool (4). In a first position of the spool (4) in the cylinder (6) a selected pair of ports (5) is connected for the flow of fluid and in a second position of the spool (4) in the cylinder (6) an alternatively selected pair of ports is so connected. Various configurations of the grooves and through passages are disclosed. The valve is particularly used to control fluid flow in reverse osmosis liquid purification apparatus. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO SPOOL VALVES This invention relates to spool valves and in particular but not exclusively to a spool valve for use in a reverse osmosis purification apparatus for the purification of water or other fluids.

It is known for spool valves to be used in fluid purification apparatus of the type as disclosed in European patent No. 0028913 in which a reverse osmosis purification module having a suitable membrane is supplied with fluid under high pressure using two or more mechanically interconnected piston-cylinder assemblies which are supplied and driven by a single low pressure supply of fluid.

More particularly the above patent discloses apparatus for the reverse osmosis purification of water or other fluid which comprises a fluid supply, a module including a reverse osmotic membrane, a fluid inlet and fluid outlet for passage of fluid over one surface of the membrane and an outlet for the passage of purified fluid out of the module from the opposite surface of the membrane together with a plurality of similar cylinders each having a piston or diaphragm dividing the cylinder into a front end and a rear end, a separate valve to the fluid inlet of the module for each cylinder, each said cylinder with its piston or diaphragm being arranged for forcing fluid from the front face of the piston or diaphragm through said separate valve to the fluid inlet of the module, at least one operating rod mechanically interconnecting said pistons or diaphragms, which operating rod or rods extend from the rear faces of said pistons or diaphragms whereby said pistons or diaphragms mechanically operate in a cyclic sequence, and valve means for the front end of each cylinder, wherein there are provided means arranged for supplying fluid under pressure from said fluid supply to the front end of each cylinder through separate non-return or controlled distribution valves constituting said valve means and in that there are also provided controlled valve means operating selectively to connect the rear end of each cylinder alternately to the fluid outlet of the module and to a discharge in synchronism with said cyclic sequence so that the pistons are driven by the applied fluid pressure.

In the simplest case only two cylinders are employed and, in this case, two pistons may be directly connected by an operating rod so that the cylinders are aligned and the pistons are connected in back to back formation.

It is an object of the present invention to provide improved valve arrangements particularly but not exclusively for use with such apparatus and to provide an improved apparatus of the type hereinbefore defined.

According to the present invention there is disclosed a spool valve comprising a housing defining an elongate throughway, a plurality of ports spaced apart along and communicating with the throughway for the inlet or outlet of fluid, a spool having an axis extending along the throughway, the spool being reciprocatable along the throughway between a first and second position, a plurality of annular resilient seals spaced along the housing and in sealing contact with the housing and the spool respectively, retaining means in the throughway locating each seal in fixed relationship with the throughway with at least one seal interposed between each pair adjacent ports spaced along the throughway, which spool includes passage means whereby in the first spool position at least one selected pair of ports is connected for the flow of fluid therebetween and in the second spool position at least one alternatively selected pair of ports is so connected.

Preferably the passage means comprises at least one grooved portion of the spool having at least one groove extending from one axial extremity of the grooved portion to the other.

Preferably the or at least one of the grooved portions comprises a plurality of grooves extending axially of the spool. An advantage of such an arrangement is that such axially extending grooves form ribbed portions of the spool between the grooves which extend axially throughout the grooved portion so as to provide radial support for the seals which might otherwise collapse radially inwardly.

It is further preferable that the or at least one of the grooves comprises a generally rectangular surface contour. An advantage of this arrangement is that manufacture of the grooves, using cutting means capable of producing an axially extending, rectangular groove, is facilitated.

Alternatively to the use of rectangular grooves, it is preferable that the or at least one of the grooves is generally diamond-shaped, with the elongate direction of the diamond-shape extending in the axial direction of the spool. An advantage of this arrangement is that as the or any groove crosses, due to the movement of the spool along the throughway, an annular resilient seal, the area of the face of the seal against which any fluid pressure in the groove acts changes as the spool moves. Thus wear of a seal due to a pressure ridge acting repeatedly over the same region of seal is reduced or eliminated. Such wear is of particular importance when a passage between the or any groove and an adjacent portion of the throughway is about to be either sealed or opened by the movement of the spool.

Alternatively the passage means may comprise at least one ducted portion of the spool having at least one aperture at one axial extremity of the ducted portion, each aperture being connected by a respective bore to a further aperture at the opposite axial extremity of the ducted portion.

Conveniently the or at least one of the bores extends between apertures which are diametrically opposed and axially spaced with respect to the spool.

It is further preferable that the or at least one aperture is generally diamond-shaped with the elongate direction of the diamond-shape extending in the axial direction of the spool. An advantage of this arrangement is that when the or any aperture crosses, due to the movement of the spool in the throughway, an annular resilient seal, the area of the face of the seal against which any fluid pressure in the aperture and bore acts changes as the spool moves. Thus, wear of a seal due to a pressure ridge acting repeatedly over the same region of seal is reduced or eliminated. Such wear is of particular importance when a passage between the or any aperture and an adjacent portion of the throughway is about to be either sealed or opened by the movement of the spool.A further advantage of the use of diamond shaped apertures is that any tendency of the 0 ring seals to be caught in and therefore damaged by the apertures is reduced.

Preferably the ports are isolated from one another when the spool is positioned at an isolating position intermediate the first and second position.

Advantageously the seals are 0 rings and the retaining means comprise annular grooves in the housing.

According to a further aspect of the present invention an apparatus for the reverse osmosis purification of fluid of the type hereinbefore defined includes a spool valve as hereinbefore disclosed for controlling flow of liquid to the module incorporating the purification membrane.

Preferably the spool valve constitutes the controlled valve means. The controlled valve means as hereinbefore defined operates selectively to connect the rear end of each cylinder alternately to the fluid outlet of the module and to a discharge in synchronism with the cyclic sequence of the apparatus.

Alternatively the spool valve constitutes the controlled valve means, a separate valve to the fluid inlet of the module for each cylinder and the controlled distribution valves for the front and each cylinder.

In å preferred embodiment the apparatus has two cylinders, these cylinders being aligned and the pistons being interconnected by a common operating rod.

Particular embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings of which: Figure 1 is a schematic drawing of an apparatus for the reverse osmosis purificiatlon of water having two cylinders and including a spool valve having ten ports, Figure 2 is a schematic drawing of an alternative apparatus having a five ported spool valve, Figure 3 is a part sectioned plan view of a ten ported spool valve having grooved portions comprising axially extending grooves, Figure 4 is a similar view of a ten ported spool valve in which the passage means comprises diametrically opposed and axially spaced apertures connected by bores, Figure 5 is a similar view of a five ported spool valve having similar apertures and bores, Figure 6 is a sectional view of the spool of Figure 3, Figure 7 is a similar view of the spool of Figure 4, Figure 8 is a view similar to that of Figure 3 but which differs from Figure 3 in that the axially extending grooves are generally diamond-shaped, Figure 9 is a sectional view of the spool of Figure 8, and Figure 10 is a drawing of a spool similar to that shown in Figure 8 and showing a method of manufacture of the generally diamond-shaped grooves.

The water purification apparatus of Figures 1 and 2 includes spool valves 1 and 2 having ten ports and five ports respectively. The construction of a ten port valve as shown in Figure 3 comprises a housing 3 defining a throughway comprising a cylindrical chamber in which a spool 4 is reciprocatable. A number of side ports 5 communicate with the chamber 6 for the inlet or outlet of fluid and these ports are axially spaced from one another.

Elastomeric 0 ring seals 7 are retained in annular grooves 8 in the housing 3 and each seal projects partially into the chamber 6 such that the spool 4 is supported in the chamber by contact with the seals.

The spool 4 includes four grooved portions 9 which are separated by solid portions 10. Each grooved portion 9 includes axially extending grooves 11 which are circumferentially spaced around the spool. The seals 7 are located intermediate adjacent ports 5 so that when the spool is positioned such that a solid portion 10 is in contact with that seal then there is no fluid flow path between those adjacent ports. If on the other hand a grooved portion 9 of the spool 4 is in registration with that seal a flow path is established between the ports through a channel formed between the grooves 8 and the housing 3. The spool and housing therefore together serve as a valve to open and close the flow path between adjacent ports depending on the axial position of the spool.

The 0 ring seals 7 are held in the grooves 8 by contact with the spool and during the period in which a ducted portion 9 is in registration with a particular seal it is held in place by contact with the axially extending ribs 12 formed between the grooves 11. The 0 ring seals 7 are thereby prevented from collapsing radially inwards.

An alternative arrangement shown in Figure 4 includes ducted portions 90 formed by apertures 13 in the spool 4 which are connected by bores 14.

Connected apertures 13 are diametrically opposed and axially spaced with respect to the spool 4. Adjacent ports 5 are connected by a channel formed by intersecting bores 13 which connect those apertures 13 which are in registration with the ports. In an alternative arrangement (not shown) axially spaced ports on diametrically opposed sides of the housing 3 may be connected by a single such bore 14.

During axial movement of the spool 4 such that an 0 ring seal 7 encounters a ducted portion 9 the seal is held in place in its groove 8 by contact with the spool and does not collapse radially inwards since the apertures 13 are selected to be small relative to the circumference of the spool.

Figure 5 shows a shorter spool suitable for use in a five port spool valve and having only two ducted portions.

Figure 8 shows a spool valve similar to that shown in Figure 3 and comprising a housing 3 defining a throughway itself comprising a cylindrical chamber in which a spool 4 is reciprocatable ie it may move between a pair of points respectively at either axial extremity of the housing 3. A number of side ports 5 communicate with the chamber 6 for the inlet or outlet of fluid and these ports are axially spaced from one another.

Whilst the embodiment of Figure 8 is similar to that shown in Figure 3, it differs from the previously described arrangement in that the axially extending grooves 100 included in grooved portion 9 of the spool 4 have a generally diamond-shaped surface contour. By the phrase "generally diamond-shaped surface contour" is meant that the grooves 100, if existing in a plane surface, would appear diamond-shaped to an observer; but the curvature of the surface of the spool 4 distorts the shape of the grooves 100 so that they do not appear as perfect diamond - like shapes.

The diamond-shaped grooves 100 act similarly to the rectangular grooves 11 of Figure 3 in that they permit selective fluid flow between adjacent ports 5, according to the position of the spool 4. However, as a grooved portion 9 including diamond-shaped grooves 100 crosses a seal 7, the area of the groove 100 adjacent the seal 7 changes as the spool moves.

Thus the area of an 0 ring seal 7 against which any fluid pressure within a groove 100 may act also changes with the position of the spool 4 relative to the 0 ring seal 7. When a diamond shaped groove 100 is moving across an 0 ring seal 7 to break a seal but the groove apex 102 has not moved sufficiently far for the seal to be breached, a pressure ridge of constantly varying size therefore acts on the face 101 of the seal 7. This pressure ridge of varying size causes wear on the seal face 101 to vary and hence prolongs the life of the seal 7.. This occurs by not subjecting the seal face 101 to a pressure ridge acting repeatedly on a constant area.

When an apex 102 of a groove 100 emerges on the opposite side of a seal 7 to that on which the bulk of the corresponding grooved portion 9 is initially located the seal is broken. However this breach of the seal initially only occurs at a point and hence strain on the seal 7 is further reduced in comparison with that effected by a rectangular groove, which causes the seal to be broken along a line and therefore causes wear over a large area of the seal face 101.

Figure 9 shows a sectioned view of the spool 4 of the Figure 8 and illustrates the triangular profile associated with diamond-shaped grooves 100.

There is shown in Figure 10 a representation of a method of manufacture of a spool 4 having diamond shaped grooves 100 as previously described. A groove 100 is cut using a rotating cutter wheel 105 mounted on a shaft 106. The cutter wheel 105 has teeth or blades 107 which produce a groove of triangular profile, although individual teeth of a cutter wheel need not themselves be of triangular profile. The cutter wheel 105 is mounted so that its axis of rotation 108 is perpendicular to the longitudinal axis 110 of the spool 4 and a groove 100 is cut by moving the cutter wheel onto the surface of the spool 4, and allowing penetration of the teeth of the cutter wheel 105 a predetermined depth into the surface of the spool 4. When a particular groove 100 has been cut the cutter wheel 105 is withdrawn and the spool 4 and/or the cutter wheel 105 indexed to a new position for cutting of a further groove 100.

This process is repeated until all the required grooves have been cut in the spool 4.

Clearly the method of manufacture shown in Figure 10 is equally applicable to the manufacture of diamond-shaped apertures for use in conjunction with the emobodiments of Figures 4 and 5, such diamond shaped apertures conferring the same advantage of reduced wear and strain on 0 ring seals as the generally diamond-shaped grooves 100 of Figures 8-10.

Both generally diamond-shaped grooves and generally diamond-shaped apertures are advantageous when the spool moves to "make" a seal, ie to close the passage between two adjacent ports, since any resulting pressure ridges will act on constantly changing areas of the inner face of an 0 ring seal as the spool moves.

The apparatus of Figure 1 includes a piston-cylinder arrangement referred to as a converter 20 having a first and second cylinder 21 and 22 respectively receiving a first and second piston 23 and 24 respectively. The pistons are arranged back to back and are connected by an operating or connecting rod 25. Ports 26 are provided in the cylinders for the input and output of fluid both forward and rearward of the respective pistons.

A reverse osmosis module 27 includes a membrane 28 and has an inlet and outlet 51 and 50 respectively for unpurified fluid and an outlet 54 for purified fluid extracted by means of the membrane 28. A source of pressurised fluid is provided by a pump 32 and circulated fluid is disposed of by means of a fluid discharge or drain 33. The converter 20 serves to boost the fluid pressure to a sufficiently high pressure for the osmosis process to operate and is itself powered by the relatively low pressure of fluid supplied by the pump 32. A spool valve 34 having ten ports is actuated by a reciprocating means 35 for driving the spool axially within its housing in alternate directions in synchronism with the reciprocating motion of the pistons 23, 24 within the cylinders 21, 22.

The spool valve 1 has ten ports 40 to 49 of which port 40 is connected to the fluid drain 33, port 41 is connected to the outlet 50 of the module 27, port 42 is connected to the fluid drain 33, port 43 is connected to the front end of the first cylinder 21, port 44 is connected to the front end of the second cylinder 22, port 45 is connected to the inlet 51 of the module 27, port 46 is connected to the pump 32, port 47 is connected to the inlet 51 of the module 27, port 48 is connected to the rear end of the second cylinder 22 and port 49 is connected to the rear end of the first cylinder 21.

In the first position of the spool 4 as shown the spool valve connects ports 41 and 49, ports 42 and 48, ports 43 and 47, and ports 44 and 46.

Pressurised fluid is thereby directed from the pump 32 into the forward end of the second cylinder 22 so as to drive the second piston rearwardly and hence the first piston 23 forwardly. Fluid in the rearward part of the second cylinder 22 is directed to the drain 33 whilst fluid in the forward part of the first cylinder 23 is pumped by the first piston at elevated pressure into the module 27. Fluid leaving the module 27 is drawn into the rearward part of the first cylinder 21 by piston action so that the fluid on each side of the first piston is at elevated pressure.

The pressure of fluid within the first cylinder 21 is elevated above that of the fluid delivered from the pump 32 because as the first piston 23 is driven forward the available volume for the fluid contained in the cylinder 21 and module 27 is decreased because of the intrusion of the connecting rod 25 into the cylinder. Also because of the presence of the connecting rod 25 the effective area of the rear face of the first piston 23 is less than that of its front face thereby applying a net rearward force to the piston 23. The second piston 24 is exposed to fluid at the pumped pressure on its front face and zero pressure at its rear face so that, provided the pumped pressure is adequate, the force acting on the first piston 23 will be overcome and the first piston will move forward accompanied by rearward movement of the second piston 24.Some of the fluid delivered to the module 27 will pass through the membrane 28 as purified product and the volume of such fluid at each stroke of the apparatus corresponds roughly to the difference in maximum available volume on either side of each piston due to the presence of the connecting rod 25.

At the end of the stroke of the pistons 23 and 24 the reciprocating means 35 is actuated to move the spool 34 into the second position so as to connect ports 40 and 49, ports 41 and 48, ports 43 and 46 and ports 44 and 45. In this condition the module 27 is supplied from the second cylinder 22 as the pistons move in the opposite direction and the roles of the respective cylinders and.pistons are exchanged.

The arrangement shown in Figure 2 includes a five port spool valve 2 which is mounted integrally in the converter 20 with the axis of the spool parallel to that of the first and second cylinders 21 and 22. The five ports of the spool valve 2 are connected to the converter and to the module 27 in the same manner as ports 40, 41, 42, 48 and 49 of the spool valve 1 of Figure 1 and additional check valves 52 are provided to perform the remaining valve functions.

The five port spool valve 2 operates selectively to connect the rear end of each cylinder 21, 22 alternately to the fluid outlet 50 of the module 27 and to the fluid drain 33 in synchronism with the cyclic sequence of the converter 20 so that the pistons 23, 24 are driven by the applied fluid pressure delivered from the pump 32. Reciprocating means is provided for reciprocating the spool 4 at the completion of each piston stroke to thereby synchronise the valve action and cyclic sequence.

The spool reciprocating means 35 may in either embodiment be hydraulic and conveniently may include additional end ports 53 (as shown in Figures 3 and 8) at each end of the housing 3 for the admission of pressurised fluid for driving the spool 4 in an axial direction. This hydraulic pressure may conveniently be taken from the pump 32. Additional 0 ring seals are then provided to isolate the end ports 53 from the side ports 5. The apparatus may also include means for sensing the position of the pistons 23 and 24 and for example this may be an electrical induction device.Alternative sensing arrangements are also possible including magnetic devices, pressure sensors for sensing the pressure peak occuring at the end of piston travel, or a pilot needle fitted either at the outer end of each main cylinder or at the centre section and in each case permitting the passage of water pressure to the relevant end of the spool. Alternatively the cyclic sequence may be controlled by a timer device.

In the embodiment of Figure 2 the cyclic sequence is shown to be controlled by a further, mechanically actuated valve 112 which is connected to reverse the position of spool valve 2 at the end of each stroke of the convertor 20. Valve 112 has a fluid supply port 118 connected to the pump 32, two ports 120, 122 selectively connectable to the fluid drain 33 and a pair of ports 124, 126 respectively connected to each of the additional end ports of spool valve 2. Valve 112 further has needle actuating means 114, 116 which respectively protrude into the rearward parts of cylinders 21 and 22.

At the instant shown in Figure 2, piston 24 is moving from right to left and therefore valve 112 is positioned so that ports 118 and 124 are connected and fluid at pump pressure is admitted to the right hand end of spool valve 2. Port 120 is connected to the fluid drain 33 and port 122 is closed. At the end of its stroke, the rear face of piston 24 strikes needle actuator 116 and reverses the position of valve 112. This causes fluid at pump pressure to be admitted via port 126 to the left hand end of spool valve 2 and this reverses the position of spool valve 2 so that the cyclic sequence of the convertor may continue without the pistons stalling. Similarly valve 112 reverses again when the rear face of piston 23 strikes needle actuator 114. On reversal of valve 112 the fluid drain 33 is open to whichever of ports 120 or 122 was previously closed, allowing fluid to drain from valve 112 as it changes position.

It will be clear that the embodiment described of using an additional valve 112 represents one of a number of methods of controlling the cyclic sequence of the apparatus. However, the technique is equally applicable to the embodiment of the ten port valve 1 of Figure 1. Further, it will be apparent that valve 11z may be a spool valve in accordance with the present invention.

A spool valve in accordance with the present invention may be constructed with any number of ports. A larger number of ports for example may be required when more than two piston-cylinder arrangements are used. The spool should preferably be of non corrosive and slippery material such as polytetrafluorethylene or other plastics material.

Alternatively the spool may be made of suitable steel or glass material. To provide additional protection to the 0 rings in such a spool valve the edges of all holes or grooves should be chamfered to avoid sharp edges.

The apparatus may operate with any suitable fluid but is particularly useful for the purification of water and may for example be used to purify sea water. Whilst the source of pressurised fluid referred to above is a pump the source could be otherwise, for example a pressurised supply from a dam.

Claims (16)

1. A spool valve comprising a housing defining an elongate throughway, a plurality of ports spaced apart along and communicating with the throughway for the inlet or outlet of fluid, a spool having an axis extending along the throughway, the spool being reciprocatable along the throughway between a first and second positions, a plurality of annular resilient seals spaced along the housing and in sealing contact with the housing and the spool respectively, retaining means in the throughway locating each seal in fixed relationship in the throughway with at least one seal interposed between each pair of adjacent ports, spaced along the throughway which spool includes passage means whereby in the first spool position at least one selected pair of ports is connected for the flow of fluid therebetween and in the second spool position at least one alternatively selected pair of ports is so connected.

2. A spool valve as claimed in claim 1 wherein the passage means comprises at least one grooved portion of the spool having at least one groove extending from one axial extremity of the grooved portion to the other.

3. A spool valve as claimed in claim 2 wherein the or at least one of the grooved portions comprises a plurality of grooves extending axially of the spool.

4. A spool valve as claimed in claim 2 or claim 3 wherein the or at least one of the grooves comprises a generally rectangular surface contour.

5. A spool valve as claimed in claim 2 or claim 3 wherein the or at least one of the grooves is generally diamond-shaped, with the elongate direction of the diamond-shape extending in the axial direction of the spool.

6. A spool valve as claimed in claim 1 wherein the passage means comprises at least one ducted portion of the spool having at least one aperture at one axial extremity of the ducted portion, each aperture being connected by a respective bore to a further aperture at the opposite axial extremity of the ducted portion.

7. A spool valve as claimed in claim 4 wherein the or at least one of the bores extends between apertures which are diametrically opposed and axially spaced with respect to the spool.

8. A spool valve as claimed in claim 6 or claim 7 wherein the aperture is generally diamond-shaped with the elongate direction of the diamond-shape extending in the axial direction of the spool.

9. A spool valve as claimed in any preceding claim wherein the ports are isolated from one another when the spool is positioned at an isolating position intermediate the first and second positions.

10. A spool valve as claimed in any preceding claim wherein the seals are 0 rings and the retaining means comprise annular grooves in the housing.

11. Apparatus of the type hereinbefore defined for the reverse osmosis purification of fluid including a spool valve as claimed in any preceding claim for controlling flow of liquid to the module incorporating the purification membrane.

12. Apparatus as claimed in claim 8 wherein the spool valve constitutes the controlled valve means operating selectively to connect the rear end of each cylinder alternately to the fluid outlet of the module and to a discharge in synchronism with the cyclic sequence of the apparatus.

13. Apparatus as claimed in claim 8 wherein the spool valve constitutes the controlled valve means, a separate valve to the fluid inlet of the module for each cylinder and the controlled distribution valves for the front end of each cylinder.

14. Apparatus as claimed in any of claims 8 to 10 having two cylinders, these cylinders being aligned and the pistons being interconnected by a common operating rod.

15. A spool valve substantially as hereinbefore described with reference to and as shown in any of the accompanying drawings.

16. Apparatus for the reverse osmosis purification of fluid substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.