GB2247737A

GB2247737A - A pneumatic valve

Info

Publication number: GB2247737A
Application number: GB9116298A
Authority: GB
Inventors: Kurt Stoll; Manfred Ruedle
Original assignee: Festo SE and Co KG
Current assignee: Festo SE and Co KG
Priority date: 1990-09-06
Filing date: 1991-07-29
Publication date: 1992-03-11
Anticipated expiration: 2011-07-29
Also published as: GB2247737B; DE4028234A1; ITMI912220A0; FR2666634A1; IT1251156B; SE503472C2; JPH04248077A; SE9102529L; GB9116298D0; ITMI912220A1; SE9102529D0; DE4028234C2

Abstract

A pneumatic valve comprises a valve housing (2) and a valve spool (1) arranged therein. Dependent on the position of switching of the valve spool (1) receiving space (5b) is in communication with one of two receiving spaces (5a, 5c). For this purpose lip seals (7) are provided between the two parts (1 and 2) and they have a lip edge (12) pointing in the axial direction. These lip seals (7) are so arranged both on the valve housing (2) and also on the valve spool (1) in such a manner that a respective lip edge is turned towards the receiving space (5a) under a higher operational pressure and furthermore during a switching movement a sealing edge (18) initially engages the rear side of the associated seal. <IMAGE>

Description

Improvements in and relating to pneumatic Valves.

The invention relates to pneumatic valves and more particularly but not exclusively to a valve comprising as one part a valve housing, in whose receiving space a valve spool as a further part, which is more particularly in the form of a round rod, is arranged for axial movement and which has a plurality of axially consecutive receiving space sections, which are connected with each other and separated from each other, respectively, in the possible switching positions in accordance with different schedules, and in the zone between the valve spool and the valve housing seals are provided, which are arranged axially consecutively, are attached to one of the two parts via a respective holding portion and are more particularly in the form of sealing rings, such seals being caused by movement over a sealing edge provided on the other respective part to shift into a sealing position during operation of the valve, in which sealing position there is a cooperation of a sealing zone, for instance in the form of a sealing rim, provided thereon, with the other part so that the seals sealingly separate sections of the receiving space with a higher operational pressure from receiving space sections with a lower operational pressure.

Valves of this type are generally multi-way valves and possess a valve spool which is for instance in the form of a flat spool or more particularly in the form of valve spool with a round cross section. The seals provided for sealing between the valve spool and the valve housing are, in the case of valves with round or cylindrical valve spools, designed in the form of sealing rings coaxially surrounding the latter. Such a valve is for instance described in the German patent 3,204,112A, in which case the sealing rings are fixedly attached to the cylindrical valve spool so as to move with it. In the case of a further valve as described in the German patent 3,043,871 the valve spool itself bears no seal and the sealing rings are held on the valve housing.

In all other cases so-called O-rings or the like are utilized as seals, which have the disadvantage that if they are worn there is no sufficient reserve of material for re-adjustment. Wear of the seals is more particularly a problem in the case of multi-way valves and it is more particularly caused by the movement over the sealing edges on the housing, even if such edges are rounded.

Furthermore owing to their compact design conventional seals only have a limited capability to allow for manufacturing inaccuracies as regards the dimensions and alignment of the valve spool and the receiving space. Then finally there is frequently the problem that the sealing rings as utilized in known valves are slightly pulled out of their positions owing to the suction effect of the emerging fluid so that leakage past them is possible.

Accordingly one object of the invention is to design a valve of the type initially mentioned which while having reduced wear in comparison with the prior art has a larger reserve of material for re-adjustment or taking up wear.

In accordance with a further object of the invention the valve is to have firmly seated seals and is to allow for comparatively large relative dimensional and fitting inaccuracies between the valve spool and the valve housing.

In order to achieve these or other purposes appearing in the present specification, claims and figures, valve comprising as one part a valve housing, in whose receiving space a valve spool as a further part, which is more particularly in the form of a round rod, is arranged for axial movement and which has a plurality of axially consecutive receiving space sections, which are connected with each other and separated from each other, respectively, in the possible switching positions in accordance with different schedules, and in the zone between the valve spool and the valve housing seals are provided, which are arranged axially consecutively, are attached to one of the two parts via a respective holding portion and are more particularly in the form of sealing rings, such seals being caused by movement over a sealing edge provided on the other respective part to shift into a sealing position during operation of the valve, in which sealing position there is a cooperation of a sealing zone, for instance in the form of a sealing rim, provided thereon, with the other part so that the seals sealingly separate sections of the receiving space with a higher operational pressure from receiving space sections with a lower operational pressure, is characterized in that the seals are in the form of lip seals, which respectively have a sealing lip arrangement comprising at least one sealing lip, the sealing lip arrangement has a form with an axial directional component towards its free end or sealing zone, which is remote from the holding part and is associated with the front side of the seal, and both on the valve housing and also on the valve spool at least one such lip seal has such an alignment that the front side of the seal having the free end or, respectively, the sealing zone is directed, as seen in the sealing position, towards a receiving space section with a higher operational pressure and furthermore on movement into the sealing position the associated sealing edge is first run over by the axial seal back side of the lip arrangement or, respectively, the back side of its sealing lip arrangement.

Accordingly lip seals are utilized as seals and such lip seals as seen in their sealing positions only make reliable sealing engagement in one of the two possible axial positions or directions of mounting when they are subjected to an axial pressure differential. The seals have such an alignment in the part between the valve spool and the valve housing that they cooperate with the axial side, which constitutes the front side, towards which the sealing lip arrangement, which generally consists only of one sealing lip, is directed, which during operation is normally subjected to a higher pressure than the following receiving space section which is adjacent thereto beyond the sealing ring. The pressure differential obtaining results in a force assisting the inherent sealing force of the seal, which is approximately proportional to the pressure differential.In order to ensure optimum pressure relationships in the transitional zone of all receiving space sections and furthermore to prevent the lip edge of a seal running against a sealing edge during the switching movement of the valve spool so that the lip is turned back and is damaged, there is the provision in accordance with the invention that both on the valve housing and also on the valve piston respectively at least one corresponding lip seal is secured so as to be dependent on the direction of sealing.

Ail in all the novel valve renders possible the use of lip seals with relatively long sealing lips so that if wear takes place there is a large reserve of material for resetting. Owing to the radial deformation possible which is better than is in the case of conventional O-rings or the like, the respective sealing lip is able to compensate for wear by deformation, and the pressure differential present during operation additionally reinforces the necessary deforming effect. The satisfactory capacity to yield of the sealing lips furthermore entails an automatic allowance for inaccuracies of manufacture between the valve housing and the valve spool. And furthermore owing to the attachment, which is alternately on the valve housing and on the valve spool, of the lip seals, the arrangement may be such that the one sealing edge associated with one lip seal, of the part able to be moved in relation to it, is only run over by the back side of the sealing lip or of the seal first, and hence it is not possible for the sealing edge and the edge of the sealing lip to foul each other and the sealing lip arrangement safely slides over the sealing edge.

The combined internal-external sealing arrangement makes it impossible for the seals to be moved into the sealing position against the lip, or "tail first since they are only approached from the opposite or "head" side.

Examples of lip seal rings are illustrated in the German patent 3,204,112, but they are not similar to the arrangement and use as in the valve in accordance with the invention.

Advantageous further developments of the invention are indicated in the claims.

The invention will now be described in more detail with reference to the accompanying drawings, which show two working embodiments thereof.

Figure 1 shows an embodiment of the novel valve in longitudinal section in the form of a 3/2-way valve, halves of the figure above and, respectively, below the longitudinal center line indicating the valve spool in its two possible positions of switching.

Figure 2 shows a simplified diagrammatic longitudinal section of a 5/2-way valve generally illustrated in the same manner as the lower half of figure 1.

In the case of the two possible configurations of the valve illustrated it is a question of piston valves with a valve spool 1 in the form of a cylinder with a circular cross section.

Accordingly the seals provided between the valve spool 1 and the surrounding valve housing 2 are annular. The valve design in accordance with the invention is however also applicable to other types of valves, more particularly of the flat spool type, in which case the seal arrangement will then extend parallel to the plane of the spool.

In the valve housing 2 of the valve in accordance with the invention there is a receiving space 3 in which the valve spool 1 is arranged so that it may be reciprocated in axially, that is to say in the longitudinal direction 4 of the valve. In this case the receiving space 3 has a plurality of axially consecutive receiving space sections 5, which in the illustrated working embodiment of figure 1 are separated with respect to each other by housing steps or in the illustrated working embodiment of figure 2 may be flush with each other. At least some of the receiving space sections 5 are connected with valve ducts 6 extending laterally into the receiving space 3, such ducts leading for instance to the same outer side of the housing, where fluid power components or other devices are able to be connected via a manifold or ducts.

The valve of figure 1 is a 3/2-way valve and it has a first receiving space section 5a, which is in communication with a source of fluid under pressure, adjoining which section on one axial side there is a second receiving space section 5b which is during operation is connected with a load and which in turn is followed in the axial direction by a third receiving space section 5c, which serves for venting and is connected for instance with the surroundings or with a means receiving fluid under pressure.

The 5/2-way valve illustrated in figure 2 is similar in design, but however on the side of the receiving space section 5a which is remote from the second receiving space section 5b - connected with the source of fluid under pressure there is a further fourth receiving space section 5d, which is adapted to be connected with a load, and this receiving space section is followed by a further receiving space section 5e functioning for venting.

The two illustrated valves have the common feature that the receiving space sections 5 present are connected and separated from each other in the two possible positions of switching in accordance with a given schedule. Thus in the case of the valve of figure 1.

in the ieft switching position shown above of the valve spool 1 the first and the second receiving space sections 5, 5a and 5b are connected with each other, while the third one (5c) is cut off and in the second switching position in the bottom part of the figure the first section 5a acted upon by the pressure is separated from the two sections 5b and 5c, which are now connected with each other.

In the case of the 5/2-way valve of figure 2 in the two positions of switching the section 5a, which is connected with the source of fluid under pressure is alternatively connected with the two adjacent sections 5b and 5d leading to loads, the respective other one of these two sections 5b and 5d being connected with the adjacent section Sc and 5e serving for venting.

The separation as regards fluid connection between the individual receiving space sections is ensured in the positions of switching by the seals, which are constituted by lip seals 7 and are located in the part between the valve spool 1 and the valve housing and, respectively, the circumferential wall of the receiving space 3 in axial succession. As already mentioned, these lip seals 7 are constituted by sealing rings arranged coaxially to the valve spool 1 and it is a question of seals, which are to be fitted in accordance with the direction of sealing in order to produce the desired sealing effect.

The lip seals 7 present are partly secured to the housing and in part arranged on, and move with, the valve spool. They each have a circumferential holding part 8 which functions to lock them on the respective part 1 or, respectively, 2, such seals being fitted for instance in annular receiving recesses 9 on the outer periphery of the valve spool 1 and, respectively, on the periphery of the receiving space 3, the seals being for instance retained with a snap-action or "buttoning" effect. Each lip seal 7 possesses a sealing lip arrangement 10, which in the case of the embodiments illustrated herein consists of a single sealing lip.

This sealing lip 7 or, respectively, sealing lip arrangement 10 radially adjoins the holding part 8 and towards its free end 12 which is remote from the holding part and which in the illustrated working embodiment is constituted by a circumferential lip edge, has a form with an axial, unidirectional component. The free end 12 is associated with the axial front side of the seal so that at the front side 13 of the seal the free end 12 is directed axially away from the sealing ring. In this respect it is naturally possible and convenient for there to be an additional radial component of slope.

For instance in the case of valve of the figure 1 and 2 different types of lip seals 7 are utilized. The lip seals 7 illustrated in figure 2 have their lips so arranged that as considered in cross section they are bent towards the front side of the seal, whereas the configuration of the sealing lips of the lip seals 7 in figure 1 is on the other hand rather more bent towards the front side 13 of the sealing ring. A point in common with the two possible modifications of the invention is that as seen in cross section at one point of the periphery of the ring there is a seal configuration which is generally U-like, the one part corresponding to the one limb of the letter U belonging to the holding part 58 and the other part to the sealing lip arrangement 10.

As regards the position of fitting of the lip seals 7 in the valve a significant point is that the front side 13 of the seal is respectively turned towards the section of the receiving space with a higher operational pressure. Accordingly in the correct position of fitting the recess 17 in the seal recess 17, which is viewed in cross section and corresponds to the U-like recess, is directed towards that receiving space which is in operation normally subjected to the higher fluid pressure.

At least when a respective lip seal 7 is for an instant not performing its sealing function, a respective lip sealing arrangement 10 will also have a radial component so that all in all in the direction of viewing and starting with the holding part 8 the part runs towards the relatively movable part and simultaneously axially to the front side 13 of the seal. The lip seal arrangement 10 is in this respect made elastic and more particularly has rubber-like properties so that it is able to be radially flared when its inner diameter is caused to increase.

There is in fact always at least a small degree of flaring every time there is an axial switching movement of the valve spool 1 and a lip seal 7 runs over a sealing edge 18, which is provided on the relatively moved part and comes into a sealing position. In this sealing position, which is shown in the figures at 19, the engagement between the corresponding lip seal 7 and a sealing surface 21, which is centered on the longitudinal axis 4, is at a sealing zone 20, which is for instance constituted by the free end 12 in the form of a sealing edge in the illustrated working embodiment, such sealing surface 21 axially directly adjoining one side of the sealing edge 18, which is associated with one respective lip seal 7. It will be clear that the sealing zone 20 may have a large area in given cases.When it assumes a sealing position 19 the corresponding lip seal 7 will be axially between two adjoining sections 5 of the receiving space, and separates them in this manner hermetically. The application of the lip seals 7 to the valve spool 1 or to the valve housing 2 is in this respect performed in such a manner that as seen in a respective sealing position 19 the axial front side of the seal 13 is turned towards that section 5 of the receiving space, which is under the higher pressure during operation. The axial pressure differential which becomes established during operation means that the sealing zone 20 is forced against the associated sealing surface 21 so that there will be sealing force generally proportional to the pressure difference.The pressing force is hence all in all dependent on the operational pressure of the valve so that there is also the advantage that the actuating force for the switching movement is automatically affected accordingly.

As a further condition for the overail length of the lip seals 7 - a condition which determines whether a lip seal ring is to be held on the valve spool 1 or on the valve housing 2 - there is the stipulation that the sealing edge 18, which is associated with one respective lip seal 7 on the other part 1 or 2, is run over on the movement into the sealing position 19, with the axial rear side 22 of the seal leading, that is to say is run over from the rear side of the sealing lip arrangement.

If accordingly we consider a lip seal 7' before a switching movement in a position 24 without any sealing action, then its sealing lip arrangement 10 will be axially spaced on the axial side opposite to the associated sealing surface 21, before the associated sealing edge 18.

During the following switching movement the rear side 22 (which may for instance be filleted or oblique) of the lip seal 7 and 7' will then slide over the sealing edge 18, the sealing lip arrangement being deformed towards the holding part 8 elastically.

When the sealing edge 18 has moved clear of the sealing zone 20 the arrangement will be in the sealing position. It is in this manner that the edge 12 of the radially spread sealing lip arrangement 10 is prevented from jamming against the one sealing edge 18 and being damaged thereby. In the case of the switching movement in the opposite direction jamming against the corner or catching of the sealing lip arrangement 10 is prevented because the transition between the sealing surface 21 and the sealing edge 18 is gradual and more particularly straight.In this connection it is of course necessary to take care to see that the length of the switching movements and of the sealing surfaces 21 and, respectively, the position of the sealing lip arrangements 7 are so matched to each other that the sealing zone 20 of one sealing lip arrangement 10 is not able to run on the side, which is opposite to the sealing edge 18, past the associated sealing surface 21, for instance over a step.

Taking all this into account in the case of all the valves of figures 1 and 2 it will be seen that in each case a first lip seal 7 and 7a is arranged fixed to the housing between the first and the second receiving space section 5 and 5b, the sealing lip arrangement 10 being directed towards the first receiving space section 5a, since in the condition in which the section 5a is suitably sealed off from the second section 5b the section 5a is subjected to a higher pressure than the following second section Sb, which is simultaneously vented.A second lip seal 7 and 7b, which is secured to the valve spool, is associated with the zone between the second and the third receiving spaces 5b and 5c, the front side 13 of the seal as considered in the sealing position being turned towards the receiving space section 5b on the load side. In the case of valve in the illustrated working embodiment of figure 2 there is on the opposite side a corresponding symmetrical arrangement with respect to a plane extending radially through the first receiving space section 5a. At any rate in this case the lip seals 7 are secured successively in the axial direction 4 alternately on the valve spool 1 and on the valve housing 2.

The lip seals 7 provided in the embodiments of the invention of figures 1 and 2 consequently have a sealing lip arrangement 10 only facing in one axial direction. A further sealing lip arrangement, possibly turned in the opposite direction and which would be able to contact a sealing edge 18 during switching movement, is not present. The sealing zone on the rear side is without lips. In the case of the sealing ring illustrated in figure 1 on the left with a cruciform cross section the use of axially opposite sealing lips does cause any disadvantage, since it does not have to run over a sealing edge. This sealing ring 26 functions only to provide a sealing action between an actuating piston 27 connected with the valve spool 1 and a piston space 28 receiving the same, such arrangement normally constituting an actuating device for the pneumatic setting of the valve spool 1.

Such actuating devices are known to the man in the art so that a detailed account thereof is not called for, In the case of the valve in accordance with figure 1 the first receiving space section 5a is also sealed off on the side, which is remote from the other sections, by means of a lip seal 7 in accordance with the invention, although in this case, because on the other hand sealing edges have to be run over, it would be possible to utilize a conventional sealing ring or indeed a cross sealing ring.

More particularly in the case of figure 2 the distance between the spool member, which is received with radial play in the valve housing 2 and the wall of the receiving space is shown on a larger scale in order to make the design features clearer. However the lip rings offer the advantage that, dependent on the lip length, they may be made very elastic and, respectively, may be designed to have a desired elasticity and thus there are large reserves of material to allow for wear. Furthermore they make possible larger tolerance specifications for the diameter. Since the arrangement in accordance with the invention ensures that the lip rings are not able to be moved into their sealing position against the grain" but from the rear end, the danger of the sealing lip being buckled owing to jamming against a sealing edge is out of the question.In order to simultaneously ensure an optimum sealing action in the case of a pressure differential between adjacent section of the receiving space, the lip rings have to be separately secured on the one hand to the valve piston and on the other hand to the housing.

The housing 2 of the valve in accordance with figure 1 is characterized by a multipart design 2. Externally it possesses a generally box-like housing cover 29 whose configuration is more particularly in the form of a parallelepipedon, into which from one cover opening 34 on the longitudinal side inner parts 30, 31 and 32 of the housing are inserted in axial succession, which cooperating with a suitable recesses constitute the receiving space 3 and the valve ducts 6. It is convenient if the receiving recesses 9 on the housing side are formed adjacent to the point of separation between two respective successive housing parts, which are hence divided in a radial plane when the housing parts 30, 31 and 32 are separated so that the lip seals 7, which are to be secured to the housing, may be fitted before the other parts of the assembly operation. It is in this manner that it is possible to make the receiving recess 9 wider adjacent to bottom of the recess without any trouble in order to ensure a reliable anchoring for the holding part and furthermore to have an axial supporting action on both sides for the seal section therein adjacent to the narrower part of the receiving space towards the receiving space 3.

It is to be pointed out in addition that the sealing edges 18 present are preferably located in the axial succession of spool and housing sections with different diameters and, respectively cross sections. More particularly the sealing edges of the housing may however as shown in figure 2 be constituted by the edges of valve ducts opening into the receiving space 3, such ducts then only having to extend over a part of the periphery of the receiving space 3.

Claims

1 A pneumatic valve comprising a valve housing as one part, in whose receiving space a valve spool as another part, which is more particularly in the form of a round rod, is arranged for axial movement and which has a plurality of axially consecutive receiving space sections, which are connected with each other and separated from each other, respectively, in the possible switching positions in accordance with different schedules, and in the zone between the valve spool and the valve housing seals are provided, which are arranged axially consecutively, are attached to one of the two parts via a respective holding portion and are more particularly in the form of sealing rings, such seals being caused by movement over a sealing edge provided on the other respective part to shift into a sealing position during operation of the valve, in which sealing position there is a cooperation of a sealing zone, for instance in the form of a sealing rim provided thereon, with the other part so that the seals sealingly separate sections of the receiving space with a higher operational pressure from receiving space sections with a lower operational pressure, wherein the seals are in the form of lip seals, which respectively have at least one sealing lip arrangement comprising a sealing lip, the sealing lip arrangement has a form with an axial directional component towards its free end or sealing zone, which is remote from the holding part and is associated with the front side of the seal or sealing zone, and both on the valve housing and also on the valve spool at least one such lip seal has such an alignment that the front side of the seal having the free end or, respectively, the sealing zone is directed, as seen in the sealing position, towards a receiving space section with a higher operational pressure and furthermore on movement into the sealing position the associated sealing edge is first run over by the axial seal back side of the lip arrangement or, respectively, the back side of its sealing lip arrangement.

2 The valve as claimed in claim 1, wherein as seen in cross section the lip seals'adjacent to the sealing lip arrangement have a form which is bent or curved towards the front side of the sealing ring.

3 The valve as claimed in claim 1 or in claim 2, wherein the lip seals have a cross section generally in the form of a letter U, and the part corresponding to one U limb belongs to the holding part and the part corresponding to the other U limb belongs to the sealing lip arrangement and the sealing recess corresponding to the U recess as seen in the sealing position thereof is turned towards the receiving space section with a higher operational pressure.

4 The valve as claimed in any one of the preceding claims 1 through 3, wherein the lip seals are arranged so as to be alternately secured to the valve spool and to the valve housing in axial succession.

5 The valve as claimed in any one of the preceding claims 1 through 4, wherein a single sealing edge is associated with each lip seal and is adjoined axially on one side by a sealing surface, and the sealing lip arrangement of the lip seal is arranged in a first switching position without a sealing action on the one axial side of the sealing edge and in a second switching position is arranged with sealing contact with the sealing surface of the other axial side of the sealing edge and in the case of a switching movement into the sealing position the sealing edge is run over with the sealing rear side ahead and in the case of a switching movement leading to a position without a sealing action and in the opposite direction it is run over with the front side of the seal ahead.

6 The valve as claimed in any one of the preceding claims 1 through 5, comprising a first receiving space section connected with a source of fluid under pressure and adjoined by at least one second receiving space section connected with a load during operation, such second receiving space section being followed by a third receiving space section which is vented or is able to be vented and more particularly is adapted to be connected to a means receiving fluid under pressure, and in one of two switching positions the first receiving space section is connected with the second receiving space section, the third space being disconnected and in the other of the two switching positions the second space is connected with the third receiving space section in such a manner that the first receiving space section is disconnected, and a first lip seal is arranged fixed to the housing in a part between the first and the second receiving space sections and a second lip seal, which is fixed to the valve spool, is associated with the part between the second receiving space and the third receiving space in such a manner that the front side of the first lip seal is turned towards the first one receiving space section and the front side of the second lip seal is turned towards the second receiving space section.

7 The valve as claimed in any one of the preceding claims 1 through 6, wherein the valve spool is in the form of a round rod more particularly having a circular cross section and it is received in a receiving space which also has a round cross section, and the lip seals are designed in the form of lip seal rings arranged coaxially to the valve rod and at a position between the valve housing and the valve.

8 The valve as claimed in claim 1, substantiaily as described in the above specification with reference to and as illustratd !fl figure 1 of the accompanying drawings.

9 The valve as claimed in claim 1, substantially as described in the above specification with reference to aRci ae llluotrated "} figure 2 of the accompanying drawings.

10 A pneumatic valve having two parts respectively comprising a valve housing and a valve member, the latter being arranged for axial movement in a receiving space of the housing which has a plurality of axially consecutive receiving space sections respectively connected with, or separated from each other in the possible switching positions in accordance with different schedules, seals being provided in the zone between the valve spool and the valve housing, the seals being arranged axially consecutively, each being attached to one of the two parts via a respective holding portion, and being caused by movement over a sealing edge provided on the other part to shift into a sealing position during operation of the valve, in which sealing position there is cooperation of a sealing zone with the other part so that the seals sealingly separate receiving space sections with a higher operational pressure from receiving space sections with a lower operational pressure, wherein the seals each have at least one sealing lip arrangement providing an axial directional component towards a free end or sealing zone, which is remote from the respective holding portion, and is associated with a front side of the seal, at least one of the seals on each of the valve housing and the valve spool having such an alignment that the free end or, respectively, the sealing zone, is directed, as viewed in the sealing position, towards the receiving space section with a higher operational pressure and, on movement into the sealing position, the associated sealing edge is first run over by the rear side of the lip arrangement of the respective seal.