GB1589851A

GB1589851A - Slide valves

Info

Publication number: GB1589851A
Application number: GB3061077A
Authority: GB
Original assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Current assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Priority date: 1976-07-24
Filing date: 1977-07-21
Publication date: 1981-05-20
Also published as: DE2633443A1; FR2359343A1; SE7708453L; FR2359343B1; SE431785B

Description

(54) IMPROVEMENTS IN AND RELATING TO SLIDE VALVES (71) We, FEsTo-MAscHINENFAsRIK GOTTLIEB STOLL, a Company organised under the laws of the Federal Republic of Germany, of Ulmer Strasse 48, 73 Esslingen a.N, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement The invention is concerned with improvements in or relating to slide valves.

Slide valves of the type having a valvemember slidable in a casing which is provided with at least two inlet and outlet bores have been used especially for the control of pneumatic or hydraulic cylinders, engines, or the like. The main problem encountered with the use of these slide valves is the difficulty in providing a reliable seal between the various inlet and outlet bores.

Until the present time the valve casing and at least the end portions of the valve member have been cylindrical, a circular gasket consisting of a resilient material being provided at either of these end sections, to be pressed against the inner wall surface of the casing bore in an essentially radial direction. These seals, which may for example be O-rings, being resilient, have the disadvantage of a poor sliding capacity; this means that relatively high displacement forces have to be applied in order to control the valve movements. In addition to this, wear is considerable each time the valve member closes or releases an inlet or outlet bore, wear being particularly great at the edge of an inner wall surface, and the service life of the seal being correspondingly short.

To overcome this difficulty, a slip ring consisting of a material with good sliding properties has been inserted between the bore wall of the casing and the resilent sealing ring which presses the slip ring against the inner wall of the cylindrical casing. The drawback of this arrangement is that in consequence of the high modulus of elasticity of materials with good sliding properties, the compressive load which must be applied in order to ensure that the seal is satisfactory has to be very great which, in turn, leads to an increase in the displacement force. Moreover, the tolerances between the external slip ring diameter and the internal bore diameter have to be very narrow. Apart from this, the radial adjustment of sealing elements which have reached the wear limit, is very difficult if not impossible.Finally, the unit is relatively costly and it is extremely difficult to produce perfect bore walls which, in order to meet the requirements, must be accurately precision machined.

It has also been proposed to arrange for valve members which move along a single plane surface with the necessary inlet and outlet bores. However, the valve slide has to provide a seal only on one side and an external force has to be used to press it against the associated surface which includes the bores, in order to prevent the slide from being lifted off the surface. It is moreover difficult to adjust the necessary compressive load accurately to the pressure in the inlet bore(s).

It is therefore understandable that as a precaution a compressive force is applied that is higher than necessary and this, in turn, entails higher displacement forces.

It is an object of the invention to provide a slide valve which is easily manufactured and preferably adjusted to compensate for wear, and is moreover favourable with regard to customer services.

According to the present invention there is provided a slide valve having a casing comprising a pair of plate members defining surfaces which are disposed in parallel planes, a valve member reciprocably slidably located between said plate members, a sealing arrangement provided on the valve member on each side thereof which is adjacent to a respective one of the plate members, each sealing arrangement defining a planar sliding surface engageable with a respective one of the parallel plane surfaces of the plate members, and a plurality of bores arranged in each of said plate members, each bore in one of said plate members being aligned across the sliding path of the valve member with a respective bore in the other of said plate members whereby, when a pair of aligned bores have a common external connection, the valve member is relieved from any differential pressure effects transversely to its slide path, and the valve member being capable of providing communication simultaneously between any one bore, the bore aligned therewith, and each of the bores at an adjacent pair of aligned bores.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing, the single figure of which is a schematic representation of an axial longitudinal section through a slide-valve according to the invention.

Referring to the drawing, a slide-valve 11 for pneumatic or hydraulic control units comprises a valve casing with two planar plates 12 and 13 which are spaced apart by a distance (a), and which are formed as planeparallel elements and accommodate therebetween a valve-slide 14 with sealing elements 15, the slide moving to and fro as indicated by the double-hcaded arrow A with the aid of a rod which is not shown in the drawing.

Each of the plates 12, 13 which may be, for example, of elongate rectangular form, or square form, is provided with continuous bores 16, 161, 1611 and 17, 171, 1711 which define inlet and outlet bores of the slide valve 11, each of the bores 16, 161, 1611 being located across slide path of of the valve slide 14 opposite a corresponding bore 17, 171, 1711.

The bores 161, 171 define inlets for a supply of pressure medium, the bores 16, 17 define connections to means to be controlled by the valve, and the bores 1611, 17define outlets to exhaust. Depending on the instantaneous position of the slide 14, the two central bores 16, 17 (as shown in the drawing) could for example be connected solely with one another, or an outer pair of bores on one side or the other, 161, 171 or 1611, 1711 could be connected with the bores 16, 17 to either deliver pressure medium to the means to be controlled or connect the latter to exhaust, because the remaining pair of bores which are located opposite each other are sealed off by the valve slide 14.The outside of the bores may be provided with a nipple connecting with a pneumatic or hydraulic line and the bores may, for this purpose, be threaded.

It is to be appreciated that the arrangement of inlet and outlet bores may differ from that shown in the drawing.

The inner surfaces 18, 19 of the two planeparallel plates 12, 13, through which the inlet and outlet bores extend are precisionmachined, or preferably lapped. The distance (a) between the two plates 12, 13 is adjustable or re-adjustable with the aid of suitable means. At the ends of the valve there are located, between the two plates 12, 13, plates or discs 35, 36, which may be resilient, and are sealed by means of O-rings 37, 38.

Adjustment is made by clamping the plates 12, 13 or more or less tightly together for example with the aid of set-screws or braces.

The valve slide 14 is defined by a pair of end sections 21, 22 preferably of oblong or square form and an integral connecting web 23 of smaller dimensions. Each of the end sections 21, 22 has, on each face which is adjacent to a respective one of the plates 12, 13, a respective groove 26, 27, the groove 26 opening towards the inner surface 18 of the upper plate 12, and the groove 27 opening towards the inner surface 19 of the lower plate 13. Into each of the grooves 26, 27, is fitted an elongate sealing element 15 which corresponds to the width of the end sections, each element 15 consisting of a sliding strip, manufactured for example from Teflon (Registered Trade Mark), polyamide, polyurethane, and a selaing strip 29 of circular cross section consisting of a highly elastic material such as Perbunan (Registered Trade Mark) or Buna (Registered Trade Mark).The sealing strip 29 rests against the bottom of the groove 26, 27, and the sliding strip 28 rests against the selaing strip 29.

The sliding strip 28 is of substantially oblong or rectangular form, and essentially fills the width of the groove 26, 27. The arrangement of the slide 14 (which may be of elongate rectangular cross-section) between the two plane-parallel plates 12, 13 is such that each sliding strip 28, controlled by the compressive force of the resilient sealing strip 29 which is inserted in a pre-stressed condition, is forced against the associated internal surface 18, 19 of the plates 12, 13. The corresponding dimension of the outer, or end sections, 21, 22 of the valve slide 14, is thereby slightly smaller than the spacing (a) between the two plates 12, 13. Sliding surfaces 31 of the sliding strips 28 thus slightly project beyond the corresponding edges 32 of the end-plates 21, 22.The sliding surface 31 and the surface 33 of each sliding strip 28, which is remote from the sliding surface 31 and rests against the sealing strip 29, is precision-machined, preferably lapped. Thus, when the sliding surface 31 is worn, the sliding strip 28 may be reversed so that the opposite surface 33 may be used as a sliding surface. In the case of the slide-valve 11 the sliding strips 28 may consist of a material with very good sliding characteristics, that is to say, the modulus of elasticity may be relatively high while the sealing strips 29 may consist of highly resilient material whose wear resistance is consequently comparatively low. Since, compared with the continuous bores 16, 17 the size of the sliding area 31 on the sliding strips 28 is very large, and since the sealing strips 29 exert an exclusively two dimensional pressure (there are no "point pressures" involved) wear in the region around the bores 16, 17 is reduced to a relatively moderate value. The considerable pre-stress of the resilient strips 29 permits major adjustments to be made should this be necessary in order to com pensate for wear.

When the cross-section of the slide is rectangular, also the grooves 26, 27 have a rectangular form; they accommodate the seals, which, for example the strip 28, may have a correspondingly rectangular cross section.

The slide valve according to the invention is easy to manufacture mainly because it is easier to machine-finish a plane surface compared with a bore wall. Similarly it is easier for the inlet and outlet bores to be provided in a plane surface compared with a bore in a cylindrical object; this applies in particular to the operations of deburring and reaming. Unlike cylindrical casings, plane-parallel plates are not affected by temperature increases and the consequential expansion of the sealing element. Even the adjustment of seals to the conditions of wear, is simpler and better. Provided that a highly slidable material has been chosen for the sliding strip and the sealing strip or the like is highly resilient, the materials may be chosen without consideration for their moduli elasticity, which means that materials having very good sliding properties may be used.

In addition to this, the sealing strips or the like which have to provide the seal and the compressive force between the sliding strip and the valve slide, may consist of any suitable material independently of its wear characteristics. Another, significant advantage is that sliding strips, especially those which are lapped on both sides, may be used on either side, that is to say they are reversible and may be turned round when one of the sliding faces has reached the wear limit.

Thus the maximum possible sliding surface and consequently the service life of the sealing element are doubled. This possibility is favourable for customers-services because the sealing and sliding properties of worn valves are easily improved.

Where the spacing of the plane-parallel plates is adjustable, the seal-pressure is very accurately adjustable, and the plate spacing is easily readjusted should this be required after prolonged service to compensate for the resultant considerable wear, in order to restore the original conditions.

Various modifications may be made without departing from the scope of the invention as defined in the appended claims.

WHAT WE CLAIM IS: 1. A slide valve having a casing comprising a pair of plate members defining surfaces which are disposed in parallel planes, a valve member reciprocably slidably located between said plate members, a sealing arrangement provided on the valve member on each side thereof which is adjacent to a respective one of the plate members, each sealing arrangement defining a planar sliding surface engageable with a respective one of the parallel plane surfaces of the plate members, and a plurality of bores arranged in each of said plate members, each bore in one of said plate members being aligned across the sliding path of the valve member with a respective bore in the other of said plate members whereby, when a pair of aligned bores have a common external connection, the valve member is relieved from any differential pressure effects transversely to its slide path, and the valve member being capable of providing communication simultaneously between any one bore, the bore aligned therewith, and each of the bores of an adjacent pair of aligned bores.

2. A slide valve according to claim 1, wherein the parallel plane surfaces of the plate members are lapped.

3. A slide valve according to claim 1 or 2, wherein each sealing arrangement is retained in position in grooves in the valve member.

4. A slide valve according to claim 3, wherein the grooves and the respective sealing arrangements extend linearly across the respective plane surfaces of the plate members.

5. A slide valve according to any of the preceding claims, wherein each sealing arrangement comprises a sliding strip which is formed of a material having high sliding characteristics, and a sealing strip which is formed of a highly resilient material.

6. A slide valve according to Claim 5, wherein the sealing strip is fitted under prestress between the sliding strip and the valve member.

7. A slide valve according to Claim 5 or 6, wherein the planar sliding surface of each sliding strip is lapped.

8. A slide valve according to Claim 5 or 6, wherein each sliding strip has a pair of opposed sliding surfaces each of which is lapped.

9. A slide valve according to any of the preceding claims, wherein the spacing between the plate members is adjustable.

10. A slide valve substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

considerable pre-stress of the resilient strips

29 permits major adjustments to be made should this be necessary in order to com pensate for wear.

When the cross-section of the slide is rectangular, also the grooves 26, 27 have a rectangular form; they accommodate the seals, which, for example the strip 28, may have a correspondingly rectangular cross section.

The slide valve according to the invention is easy to manufacture mainly because it is easier to machine-finish a plane surface compared with a bore wall. Similarly it is easier for the inlet and outlet bores to be provided in a plane surface compared with a bore in a cylindrical object; this applies in particular to the operations of deburring and reaming. Unlike cylindrical casings, plane-parallel plates are not affected by temperature increases and the consequential expansion of the sealing element. Even the adjustment of seals to the conditions of wear, is simpler and better. Provided that a highly slidable material has been chosen for the sliding strip and the sealing strip or the like is highly resilient, the materials may be chosen without consideration for their moduli elasticity, which means that materials having very good sliding properties may be used.

In addition to this, the sealing strips or the like which have to provide the seal and the compressive force between the sliding strip and the valve slide, may consist of any suitable material independently of its wear characteristics. Another, significant advantage is that sliding strips, especially those which are lapped on both sides, may be used on either side, that is to say they are reversible and may be turned round when one of the sliding faces has reached the wear limit.

Thus the maximum possible sliding surface and consequently the service life of the sealing element are doubled. This possibility is favourable for customers-services because the sealing and sliding properties of worn valves are easily improved.

Where the spacing of the plane-parallel plates is adjustable, the seal-pressure is very accurately adjustable, and the plate spacing is easily readjusted should this be required after prolonged service to compensate for the resultant considerable wear, in order to restore the original conditions.

Various modifications may be made without departing from the scope of the invention as defined in the appended claims.

WHAT WE CLAIM IS: 1. A slide valve having a casing comprising a pair of plate members defining surfaces which are disposed in parallel planes, a valve member reciprocably slidably located between said plate members, a sealing arrangement provided on the valve member on each side thereof which is adjacent to a respective one of the plate members, each sealing arrangement defining a planar sliding surface engageable with a respective one of the parallel plane surfaces of the plate members, and a plurality of bores arranged in each of said plate members, each bore in one of said plate members being aligned across the sliding path of the valve member with a respective bore in the other of said plate members whereby, when a pair of aligned bores have a common external connection, the valve member is relieved from any differential pressure effects transversely to its slide path, and the valve member being capable of providing communication simultaneously between any one bore, the bore aligned therewith, and each of the bores of an adjacent pair of aligned bores.
2. A slide valve according to claim 1, wherein the parallel plane surfaces of the plate members are lapped.
3. A slide valve according to claim 1 or 2, wherein each sealing arrangement is retained in position in grooves in the valve member.
4. A slide valve according to claim 3, wherein the grooves and the respective sealing arrangements extend linearly across the respective plane surfaces of the plate members.
5. A slide valve according to any of the preceding claims, wherein each sealing arrangement comprises a sliding strip which is formed of a material having high sliding characteristics, and a sealing strip which is formed of a highly resilient material.
6. A slide valve according to Claim 5, wherein the sealing strip is fitted under prestress between the sliding strip and the valve member.
7. A slide valve according to Claim 5 or 6, wherein the planar sliding surface of each sliding strip is lapped.
8. A slide valve according to Claim 5 or 6, wherein each sliding strip has a pair of opposed sliding surfaces each of which is lapped.
9. A slide valve according to any of the preceding claims, wherein the spacing between the plate members is adjustable.
10. A slide valve substantially as hereinbefore described with reference to the accompanying drawing.