GB2189007A - A liquid flow control valve - Google Patents

Abstract

A liquid flow control valve of the spool and sleeve type has a flow control aperture defined by circular metering edges 18, 19 on the spool and sleeve respectively and an annular flow passage 20 downstream of the aperture which leads to one or more outlet edges 38 extending around the sleeve, the passage including an annular recess 32 of concave axial cross section on the spool. A by-pass flow passage 35 extends from one or more inlets 36 in said recess to one or more outlets 37 on the spool surface opposite said outlet edge or edges 38, the by-pass outlets 37 discharging radially outwardly toward the outlet edge or edges to reduce the formation of cavitation plumes in the liquid flow passing from the annular passage over the outlet edge or edges. <IMAGE>

Description

SPECIFICATION A liquid flow control valve This invention relates to liquid flow control valves, and in particular to valves of the spool and sleeve type in which a spool is movable along the axis of the sleeve or bushing to control the flow of liquid between inlet and outlet ports in the sleeve.

In such a valve it is desirable to shape the parts in such a way as to minimise the changes in the forces acting on the spool with changes in the extent of opening of the valve.

It is also desirable in the interest of noise reduction to minimise the extent of flow disturbance or cavitation resulting from the flow of liquid around sharp corners.

These problems have been addressed in the publication Fluid Power Control edited by Blackburn et al, published by The Technology Press of M.I.T. and John Wiley & Sons inc 1960 at pp 304-310 and in PCT/GB83/001 03.

The present invention is concerned with further improving the noise reduction properties of a valve of this type.

According to the present invention there is provided a liquid flow control valve comprising a spool slidable within a sleeve, the sleeve having at least one inlet port and at least one outlet port, the spool having an annular recess therein defining part of a flow passage leading from the inlet port to the outlet port, the spool being movable axially with respect to the sleeve from a closed state in which surfaces of the spool and sleeve abut one another to close the flow passage, to an open state in which said surfaces are spaced from one another to form an aperture whose dimensions control the rate of flow through the flow passage, the recess being disposed downstream of the aperture and having a profile which, in sections containing the axis of the spool, has a concave surface, the sleeve having an outlet edge downstream of said recess over which liquid can flow to said outlet port, the spool having a by-pass passage therein leading from at least one inlet aperture disposed in said recess to at least one outlet aperture disposed in the spool surface opposite said edge whereby liquid flow discharged from the or each outlet aperture acts on liquid flow discharged over said edge along the outside of the spool in a sense to reduce cavitation in the liquid flow around said edge.

One embodiment of a liquid flow control valve according to the invention will now be particularly described by way of example with reference to the accompanying drawings in which: Figure 1 is an axial section through the valve; Figure la is an enlarged view of part of the valve of Fig. 1; Figures 2 and 3 are sections on the lines ll-ll and Ill-Ill through the spool of the valve of Fig. 1.

As shown in the drawing, the valve comprises a valve spool 10 which fits slidingly within a valve sleeve 11. The illustrated valve is a four-way valve having a centrally located inlet supply port 12 and two inlet/outlet ports 13,14 which conduct liquid between the valve and a load 15 via ducts 16,17.

Considering the left hand end of the valve, in the position of the spool as shown, a metering edge 18 on the spool is spaced from a metering edge 19 on the sleeve 10 to provide an aperture which permits liquid to flow from the load 15 through a passage 20 to an outlet in the form of return port 21.

In this position of the spool, a further pair of metering edges 22,23 in the sleeve and spool are spaced apart to permit liquid to flow from the inlet supply port 12 via the aperture defined by edges 22,23 to the load 15. The load 15 is conveniently a piston 15a movable in a cylinder 15b and under these conditions, the piston is caused to move to the left.

While the spool is in this position, surfaces on the spool engage corresponding surfaces on the sleeve to prevent flow from the inlet supply port 12 into the duct 16 and from duct 17 into the right hand end of the valve.

The right hand and left hand ends of the spool and sleeve are similarly shaped and it will be evident that if the spool is moved to the left in Fig. 1, the apertures defined by edges 18,19 and 22,23 are closed, and apertures defined by the corresponding edges 24,25 and 26,27 are opened to permit flow in the opposite directions in duct 16,17. This will cause the piston 1 5a to move in the opposite direction i.e. to the right in Fig. 1.

The passage 20 is defined between the spool 10 and sleeve 11 and comprises an annular recess formed in the outer face of the spool. In cross sections containing the axis of the spool, the profile of the recess comprises a step formed by a radial surface 30 and an axial surface 31 immediately downstream of aperture 18,19, which leads into a concave surface 32. The outlet end of the concave surface 32 leads into a straight surface 33, the passage between surface 33 and the inner surface of the sleeve converging toward the outlet formed by return port 21.

The concave surface is defined by an arc of circle extending over an angle of 130"-140", preferably 134 -138 . This results from the tangent to the inlet end of the concave surface defining an angle of preferably 21 -23 with a plane perpendicular to the spool axis.

The tangent to the outlet end of the concave surface is disposed at a similar angle. The straight surface 33 forms part of a frustoconical surface coaxial with the spool and having a cone angle preferably of 28O to 32 .

The opposite ends of the spool are each formed with a by-pass passage 35 whose inlet is formed by at least one inlet aperture 36, and preferably eight such apertures equidistantly spaced apart, in the bottom of the concave surface. The outlet of the by-pass passage is formed by at least one outlet aperture 37 disposed opposite the return port 21. Preferably eight such outlet apertures 37 are provided, each disposed opposite a separate return port 21.

The, or each, return port 21 is located downstream of an edge 38 formed on the inner surface of the sleeve and lying in a plane perpendicular to the spool axis, so as to direct by-pass liquid flow radially outwardly on to this edge.

In operation of the valve in the position shown in Fig. 1, liquid flow through the apertures 18,19 impinges on the upstream edge of the concave surface 32 and is caused to flow around the concave surface setting up a vortex flow which substantially reduces noise by reducing cavitation in the liquid flow. As the liquid flow progresses through the converging part of the passage between surface 33 and the inner surface 12a of the sleeve, pressure increases until the liquid reaches the downstream end of the frusto-conical surface of the spool.

As the flow continues and passes radially outwardly over the edges 38 at the entrance to the return ports 21, there is a tendency for cavitation plumes to form immediately downstream of the edges 38. However, radially outward flow from the outlet apertures 37 directed against the edges 38 forces the liquid passing over these edges to adhere more closely to the edges and so reduce such cavitation effect, and the corresponding noise level.

A further advantage of the by-pass flow is that liquid flow entering the inlet apertures 36 reduces or prevents circumferential flow occuring around the concave surface 32.

Claims (6)

1. A liquid flow control valve comprising a spool slidable within a sleeve, the sleeve having at least one inlet port and at least one outlet port, the spool having an annular recess therein defining part of a flow passage leading from the inlet port to the outlet port, the spool being movable axially with respect to the sleeve from a closed state in which surfaces of the spool and sleeve abut one another to close the flow passage, to an open state in which said surfaces are spaced from one another to form an aperture whose dimensions control the rate of flow through the flow passage, the recess being disposed downstream of the aperture and having a profile which, in sections containing the axis of the spool, has a concave surface, the sleeve having an outlet edge downstream of said recess over which liquid can flow to said outlet port, the spool having a by-pass passage therein leading from at least one inlet aperture disposed in said recess to at least one outlet aperture disposed in the spool surface opposite said edge whereby liquid flow discharged from the or each outlet aperture acts on liquid flow discharged over said edge along the outside of the spool in a sense to reduce cavitation in the liquid flow around said edge.

2. A valve according to claim 1 having one or more outlet edges on said sleeve, the spool having one or more inlet apertures to the by-pass passage and the one or more outlet apertures each being disposed opposite a said outlet edge.

3. A valve according to claim 1 or claim 2 wherein the concave surface of the spool recess adjoins, at its downstream end, a frustoconical surface which is divergent in the downstream direction.

4. A valve according to any preceding claim wherein the concave surface extends over an arc of a circle of 130 -140 preferably 134 -138 extent.

5. A valve according to any preceding claim wherein the frusto-conical surface diverges at an angle of 28"-32".

6. A liquid flow control valve substantially as herein described with reference to the accompanying drawings.