GB2094909A - Sealing device for pneumatic and hydraulic control instruments - Google Patents

Abstract

A sealing device for pneumatic and hydraulic control instruments consists of a sealing ring (3), which seals a closing member (2) displaceably mounted in a housing (1). Two stops (4, 5) are provided for the sealing ring (3), one (4) of which stops is disposed on the housing (1) and the other (5) on the closing member (2). When the sealing ring (3), which can be arranged between brace rings (6, 7), is acted upon on one side by a pressure medium at (9), it is supported by the stop (5) and moves with the member (2), the ring (3) sealing against the housing (1) at its outer circumference. When the stop (4) prevents further movement of the ring (3), the latter seals against the member (2) at its inner circumference. The pressure-loaded surface can therefore be altered without using other components. The device can be incorporated in a control valve (Fig. 6, not shown) where a valve member (26) is maintained seated whether pressure medium is admitted at (27) or at (23). <IMAGE>

Description

SPECIFICATION Sealing device for pneumatic and hydraulic control instruments The invention relates to a sealing device for pneumatic and hydraulic control instruments, such os pistons, slides and valves, with a sealing ring which seals a closing member displaceably mounted in a housing.

Sealing devices of this type are used not only for the pistons of control and working cylinders, but also for the pressure-tight sealing of other displaceable machine parts, such as valve shutter members, pressure-tight bushings etc. If, for example, directional control valves are actuated by pistons acted upon by a pressure medium, it is important in many cases for piston cross sections of different sizes to be operative for switching backwards and forwards. In other cases, however, piston cross sections of the same size are required. Special pistons therefore have to be provided for each case. It is necessary to mount another cylinder together with pistons and fittings in order to change a finished valve over to a piston of a different diameter.

The object of the invention is to improve the hitherto known sealing devices such that the pressure-loaded surface can be altered without using other components.

The invention lies in the fact that two stops are provided for the sealing ring arranged between the housing and the closing member, one of which stops is disposed on the housing and the other on the closing member. When the closing member is acted upon by pressure medium the sealing ring comes into contact with one stop and seals against the closing member at its inner edge and the housing at its outer edge. When it is firmly in contact with the housing, only the closing member moves when pressure is applied, the effective cross-sectional surface of the displaceable closing member corresponding to the surface defined by the inner circumference of the sealing ring.

However, when the sealing ring lies against the stop of the closing member, it moves with the latter when pressure is applied. In this case the effective surface which is acted upon as a whole by the pressure medium is determined by the outer circumference of the sealing ring and corresponds to the surface defined by the outer circumference. The pressure-loaded surface which is sealed by the sealing ring can thus be altered in a simple manner.

If, for example, the two stops of the sealing ring face one another and the sealing ring thus contacts one stop in one direction of movement and the other stop in the other direction of movement, the size of the pressure-loaded effective surface of the closing member depends upon the side of the sealing ring from which the pressure medium is supplied. The stops can, however, also be arranged such that the sealing ring comes into contact with them in the same direction of movement, and further provisions enable the sealing ring to contact one or other of the stops, as desired. In order to facilitate this, it is possible, according to the invention, to arrange a brace ring on at least one side of the sealing ring between the latter and the end stop.The effective cross-sectional surface of the closing member can be altered by omitting, exchanging or turning brace rings which are preferably of different construction.

According to a further embodiment of the invention, the brace ring is stepped at its outer circumference and only projects radially at one end with a collar into the region of the stop provided on the housing. If this brace ring is mounted such that its collar lies against the sealing ring, but its other end lies against the stop of the closing member, the sealing ring is displaced together with the closing member when pressure is applied, so that the greater surface, defined by the outer circumference of the sealing ring, becomes effective. However, if the brace ring is mounted so that it is turned through 1 800, its collar comes into contact with the stop of the housing at a correspondingly earlier point in time, the sealing ring remains stationary and only the closing member is displaced under the effect of the pressure medium.Only the smaller surface of the closing member is effective in this case and the length of the step of the brace ring preferably corresponds to the travel of the closing member. If two brace rings are provided, the sealing ring can be clamped in a mounting position between these two brace rings at the inner wall of the housing.

In a further embodiment the sealing ring can be arranged in a slide ring with sealing lips provided at the inner and outer circumference. The sealing ring presses the sealing lips inwards and outwards in a radial direction, thus providing a good seal.

The slide ring, which may consist of a material with good antifriction properties, e.g. a plastics material, reduces the sliding friction between the sealing ring and the housing and the closing member. As the slide ring also forms the brace ring, a special ring for this is unnecessary.

The sealing device according to the invention enables the operating pistons to be provided with a greater or a smaller effective cross section, e.g.

upon the actuation of directional control valves, without using new components and merely by altering the parts which are already provided. If, when the actuating pressure is the same, the directional control valve is always to assume a certain switching position, the piston having the greater cross section and acting in the relevant direction is selected. There is, however, no preferred switching position if both pistons have the same cross section. Different requirements of the actuation of the directional control valve can therefore be taken into account simply by altering the operating pistons. The use of other components is not necessary and stock keeping is correspondingly simplified.

The sealing device according to the invention can, however, also be used with other control valves, particularly with seat valves, e.g. in an embodiment with a valve housing, which comprises two pressure connections for the supply and removal of controlled pressure medium, and a control connection. A control valve of this type with the sealing device according to the invention is characterised in that the closing member sealed by the sealing ring is displaceably arranged in a bore between the two pressure connections, comprises a through-bore which can be closed by a sealing member and is connected to the shutter member of the control valve, the surface sealed by the shutter member of the control valve being greater than the surface enclosed by the inner circumference of the sealing ring, but smaller than the surface enclosed by the outer circumference of the same.This construction provides the advantage that, depending upon the side from which the pressure of the controlled pressure medium acts on the closing member, the sealing ring is always displaced such that a resultant force is produced in the closing direction of the shutter member of the control valve. It is therefore possible to exchange the pressure supply and release connections without impairing the operation of the control valve. In one instance a control valve which is closed in the non-actuated state is obtained, but in the other case an embodiment which keeps the pressure medium inlet open in the non-actuated state.

Further details and advantages of the invention will become apparent from the following description of embodiments with reference to the drawings, in which figure 1 shows a schematic axial cross section of the sealing device according to the invention, figure 2 the sealing device according to figure 1 in a mounting position, figures 3 and 4 a variant in two different mounting positions, figure 5 a directional control valve with the sealing device according to the invention in axial cross section and figure 6 a seat valve, in which the sealing device according to the invention is used, also in axial cross section.

According to figures 1 to 4, a closing member 2, e.g. a piston, is mounted so as to be axially displaceable in a housing 1. A sealing device, consisting of a sealing ring 3, is disposed between the housing 1 and the piston 2. The housing 1 comprises a stop 4 formed, for example, as a step, for the sealing ring 3, and a stop 5, formed by a radially projecting collar, is disposed on the closing member 2. Two brace rings 6 and 7, which cooperate directly with the stops 4 and 5, are arranged on both sides of the sealing ring 3. The brace ring 6 has a stepped outer circumference and is provided at one end with a radially projecting collar 8. According to figures 1 and 2, the brace ring 7 is rectangular and its outer circumference abuts the housing 1.A control pressure chamber 9, which is closed by a housing cover 10, with the interposition of a seal 11, is disposed at the front end of the closing member 2.

In the arrangement according to figure 1 the brace ring 6 is pushed along the closing member 2 such that its end lies against the stop 5. The other end, provided with the collar 8, of the brace ring 6 supports the sealing ring 3. The second brace ring 7 is disposed on the other side of the sealing ring 3 and abuts the cover seal 11. If a pressure medium is admitted to the control pressure chamber 9 via a connection which is not shown, the sealing ring 3 is supported via the brace ring 6 and the stop 5 on the closing member 2 and moves with the latter when it is displaced. Sealing against the housing 1 is effected at the outer circumference of the sealing ring 3. The effective cross section of the closing member 2 which is acted upon by pressure medium therefore corresponds to the surface enclosed by the outer circumference of the sealing ring 3.However, as soon as the collar 8 comes into contact with the stop 4, the sealing ring can no longer move with the closing member 2 and if the closing member 2 has not yet reached the end of its path of travel, it can move further under the effect of the pressure medium. However sealing is then effected at the inner circumference of the sealing ring 3. The pressure-loaded effective surface is smaller in this case and only corresponds to the surface enclosed by the inner circumference of the sealing ring 3.

Figure 2 shows another mounting position of the brace rings 6 and 7. The brace ring 7 abuts the stop 4 in this arrangement. The stepped brace ring 6 is disposed on the other side of the sealing ring 3 and the collar 8 abuts the sealing ring 3. The two brace rings 6, 7 together with the sealing ring 3 form a width which corresponds to the spacing between the stop 4 and the cover seal 1 1. The sealing ring 3 is then clamped between the two brace rings 6,7 at the inner wall of the housing 1.

If pressure medium is admitted to the control pressure chamber 9, only the closing member 2 is thus displaced and sealing takes place at the inner circumference of the sealing ring 3. This also determines the size of the pressure-loaded effective surface. Two different effective crosssectional sizes of the closing member 2 can thus be obtained with the same components by simple exchanging the brace rings 6 and 7, as illustrated in figures 1 and 2.

The variants illustrated in figures 3 and 4 correspond to the sealing device which is provided in the case of the directional control valve shown in figure 5. According to figure 5, a connecting device 12 is displaceably mounted in the housing 1 of the directional control valve and controls the connection between the individual connections 1 5 by means of seals 13 and 14. The connecting device 12 is displaced by pistons 1 6 and 17, which are inserted in bores of the housing 1 as closing members. The sealing device of the pistons 1 6 and 1 7 is formed in a manner similar to the embodiment of figures 1 and 2. As shown in figures 3 and 4, the sealing ring 3 is arranged in a slide ring 18, which comprises sealing lips 1 9 both at the inner and outer circumference. The slide ring 18 is at the same time formed as the brace ring 6 with the collar 8 which cooperates with the stop 4 on the housing 1. The arrangement of the brace rings 6 and 7 according to figure 3 corresponds to that according to figure 1, sealing being effected at the circumference of the outer sealing lip 1 9. However, in the mounting position according to figure 4 the sealing point is at the inner sealing lip 19, thus producing the same effoct as in the embodiment according to figure 2.

In the case of the directional control valve according to figure 5 the slide rinJ 18, which forms the brace ring 6, and the drape ring 7 are mounted on the left-hand side, as shown in figure 3. If pressure is applied to the piston 16, the sealing ring 3 thus moves together with the piston, so that sealing is effected at the outer circumference of the sealing lip 1 9, which is pressed against the housing 1 by the sealing ring 3. However the piston 1 7 on the right-hand side in figure 5 is sealed by a sealing device arranged according to figure 4, where the sealing ring 3 is clamped between the slide ring 18 and the brace ring 7, so that sealing is effected at the inner circumference of the slide ring 1 8 and therefore at the inner sealing lip 1 9.If the two servo pistons 16 and 17 are acted upon by a pressure medium which is under the same pressure, the connecting device 12 is always moved into its right-hand end position owing to the greater piston surface of the piston 16. The effective cross-sectional surfaces of the piston 1 6, 1 7 can be altered by simply exchanging the brace rings 6,7 or by turning the slide ring 18, without the necessity of using other spare parts. The two pistons 1 6, 1 7 can be assembled with effective surfaces of the same or different size, as desired.

The control valve illustrated in figure 6 consists of a housing 1, in which a closing member 2 is displaceably mounted. The latter is sealed in the housing 1 by a sealing ring 3, for which a stop 5, formed by a collar, is provided on the closing member 2. An insert 21 is secured in an enlargement of the housing 1 by means of a connecting screw 20 and forms, with rib-shaped extensions, the stop 4, rigidly connected to the housing 1, for the sealing ring 3. The closing member 2 comprises a through-bore 22, which connects the connecting screw 20 forming the control connection to a pressure connection 23.

The through-bore 22 can be closed against the force of a spring by a sealing member 25 formed as a push button. The lower end of the closing member 2 comprises a head-like enlargement, which forms the shutter member 26 of the control valve controlling the connection between a further pressure connection 27 and the connecting screw 20. A spring 28 pushes the shutter member 26 onto its valve seat formed by the insert 21.

If the pressure connection 27 is used as an inlet for the supply of pressure medium, the pressure acts on the sealing ring 3 and moves the latter upwards until it lies against the stop 5 of the closing member 2, as illustrated in figure 6. This pressure simultaneously acts on the conical shutter member 26, but in the opposite direction.

The surface sealed by the shutter member 26 is smaller than the surface enclosed by the outer circumference of the sealing ring 3. The force acting upwards on the closing member 2 is then greater, so that the shutter member 26 keeps its valve seat closed irrespective of the pressure value. The pressure medium inlet is thus closed when the control valve is in the non-actuated state. Pressure is removed from a pneumatic or hydraulic instrument, which is connected to the connecting screw 20, by the pressure connection 23. Thf control valve is opened bv pressing down the sealing member 25, the through-bore 22 initially being closed and then the shutter member 26 being raised from its seat.

If the pressure connections 23 and 27 are exchanged and the pressure media m is thus supplied through the connection 23 and the pressure connection 27 is used to release pressure, the pressure medium acts on the sealing ring 3 from above and moves the latter downwards until it lies against the stop 4 rigidly connected to the housing 1, as indicated by a broken line in figure 6. In this position the sealing ring 3 seals the closing member 2 along its inner circumference, so that the pressure-loaded effective surface corresponds to the surface enclosed by the inner circumference of the sealing ring 3. This surface is smaller than the surface sealed by the shutter member 26. As pressure from the connection 23 acts upon the underside of the shutter member 26 via the through-bore 22, the force acting upwards on the closing member 2 is predominant in this case as well. Pressure medium constantly acts upon an instrument connected to the connecting screw 20 when the valve is not actuated. The through-bore 22 is closed by pressing down the sealing member 25 and the shutter member 26 is subsequently raised from its valve seat, whereupon pressure can be released through the pressure connection 27.

The connections can therefore be exchanged as desired in the case of the seat valve according to figure 6, so that it is possible to use the same valve irrespective of whether the pressure medium passage through the valve in the non-actuated state is to be open or closed. The tightness of the control valve is guaranteed in both cases, as in both cases the locking spring is assisted by a pressure which acts upon the closing member and always operates in the closing direction of the valve shutter member on account of the displaceable sealing device.

Claims (7)

1. Sealing device for pneumatic and hydraulic control instruments, such as pistons, slides and valves, with a sealing ring which seals a closing member displaceably mounted in a housing, characterised in that two stops (4, 5) are provided for the sealing ring (3) arranged between the housing (1) and the closing membe (2), one (4) of which stops is disposed on the housing (1) and the other (5) on the closing member (2).

2. Sealing device according to claim 2, characterised in that a brace ring (6, 7) is arranged on at least one side of the sealing ring (3) between the latter and the stop (4, 5).

3. Sealing device according to claim 2, characterised in that the brace ring (61 is stepped at its outer circumference and only projects radially at one end with a collar (8) into the region of the stop (4) provided on the housing (1).

4. Sealing device according claim 3, characterised in that the length of the step of the brace ring (6) corresponds to the travel of the closing member (2).

5. Sealing device according to claim 2, 3 or 4, characterised in that two brace rings (6, 7) are provided, between which the sealing ring (3) can be clamped at the inner wall of the housing (1) (figure 2).

6. Sealing device according to one of claims 1 to 5, characterised in that the sealing ring (3) is arranged in a slide ring (18) with sealing lips (19) provided at the inner and outer circumference, the slide ring (18) at the same time being formed as the brace ring (6) (figures 3 and 4).

7. Control valve with a sealing device according to one of claims 1 to 6, comprising a valve housing, which comprises two pressure connections for the supply and removal of the controlled pressure medium and a control connection, characterised in that the closing member (2) sealed by the sealing ring (3) is displaceably arranged in a bore between the two pressure connections (23, 27), comprises a through-bore (22) which can be closed by a sealing member (25) and is connected to the shutter member (26) of the control valve, the surface sealed by the shutter member (26) of the control valve being greater than the surface enclosed by the inner circumference of the sealing ring (3), but smaller than the surface enclosed by the outer circumference of the same (figure 6).