GB2154303A

GB2154303A - Gate valve

Info

Publication number: GB2154303A
Application number: GB08428227A
Authority: GB
Inventors: Erwin Winklmann; Manfred Gladisch
Original assignee: Deutsche Babcock Werke AG
Current assignee: Deutsche Babcock Werke AG
Priority date: 1984-02-17
Filing date: 1984-11-08
Publication date: 1985-09-04
Also published as: IT1183352B; FR2559869B1; GB8428227D0; DE3405681C2; IT8519533A0; ATA337584A; DE3405681A1; GB2154303B; AT390310B; FR2559869A1

Abstract

A gate valve comprises a gate formed by two parallel plates (8, 9) which are held at a spacing in the unloaded state by helical springs (13) and are provided with sealing rings (11, 12, 16, 17) at mutually remote and mutually facing sides thereof. The plates (8, 9) interengage with an annular clearance fit by way of a centring projection (18) and recess (19). The diameters d2, d1 of the projection (18) end of the sealing rings (16, 17) at the mutually facing plate sides are greater than the diameter d of the sealing rings (11, 12) at the mutually remote plate sides. Sealing rings (11, 12) cooperate with seals (7, 6) on valve seats (5, 4), and flour passages (14, 15) extend through the plate (8). <IMAGE>

Description

SPECIFICATION Valve The present invention relates to a valve, and has particular reference to a gate valve with two parallel plates arranged in a flow duct in a housing.

In such a slide valve, a gap is present, according to the side of the pressure loading between the plates or between one plate and a sealing ring at the housing. A connection between the interior of the housing and the pressure-conducting side of the valve is always present by way of the gap either directly or together with a bore in one of the plates so that excess pressure, possibly due to heating of the medium in the flow duct, does not arise in the housing.

In a known slide valve (DE-PS 22 49 601), a projection provided on one of the plates has a smaller diameter than sealing rings at the housing, whilst sealing rings arranged internally and externally of the area between the plates are disposed at the height of the sealing rings at the housing. By reason of this construction, the known valve requires a certain pressure difference of about 5 to 10 bar, according to nominal width, for the sealing-off on a pressure loading on the plate without the bore. This pressure difference is generally present in the usual operating conditions.

Leakages can occur in the range of smaller pressure differences when the effective pressure on the entry side is equal to or slightly greater than the sum of the spring force and pressure acting on the exit side.

It would thus be desirable to improve such a valve so that sealing-off in all pressure ranges is ensured with the same manner of function in respect of a constant pressure relief.

According to the present invention there is provided a valve comprising a housing defining a flow duct and two parallel valve plates movably arranged in the duct.and resiliently biassed away from each other to be spaced apart in an unloaded state thereof, one of the plates being provided with a passage therethrough from one major face to the other and each of the plates being provided with respective centring means engaging the centring means of the other plate with an annular clearance therebetween and further provided with a first sealing ring co-operable with the first sealing ring of the other plate and a second sealing ring co-operable with a respective third sealing ring which is arranged in the housing and has a diameter smaller than that of each first ring and of the annular clearance.

In a preferred embodiment the two parallel plates, which interengage by way of the centring means, are held by spring means at a spacing in the unloaded state and are each provided with respective sealing rings arranged internally and externally of the area between the plates. The internal sealing rings and the external sealing rings are arranged opposite sealing rings at the housing and one of the plates is bored through in axial direction. The internal sealing rings and the centring means are arranged on a greater diameter than the sealing rings at the housing, while the diameters of the internal sealing rings and of the centring means are about equal and the centring means have a clearance fit. The centring means may have a greater diameter than the internal sealing rings. Preferably, the spring means have a flat characteristic.

Due to the increase in the diameters of the centring means and of the internal sealing rings, an increased area, on which the pressure of the entry side can act, is formed when the plate without the bore has lifted off from the sealing ring at the housing in the range of smaller pressure differences. Through the thus increased area and the pressure, an additional force is produced, which overcomes the force acting from the opposite side and effects sealing interengagement of the internal sealing rings. Thereby, the valve seals off under the aforesaid pressure conditions and forms a gap by way of which the interior of the housing communicates with the entry side.

The clearance fit in the centring means is so chosen that a throttling is provided to permit only a slow decay of the pressure towards the entry side so that the full pressure can act at the increased area after the lifting-off of the plate.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a schematic longitudinal section of part of a gate valve embodying the invention.

Referring now to the drawing, there is shown a gate valve comprising a housing 1 with two lateral stub pipes 2 and 3 which, according to pressure loading, respectively represent the entry side and exit side of the valve. Seating rings 4 and 5, which at their facing ends having sealing rings 6 and 7, are arranged in the housing 1 in the notional projection of the stub pipes 2 and 3 and welded in place.

Two parallel plates 8 and 9 are suspended at a spindle 10, by way of which the plates 8 and 9 are brought into open setting or into a closed setting between the sealing rings 4 and 5. The plates 8 and 9 are provided with sealing rings 11 and 1 2 at their mutually remote faces, which sealing rings are disposed opposite the sealing rings 6 and 7 at the housing and co-operate therewith.

The plates 8 and 9 are held at a spacing in the unloaded state by spring means so that a gap s is present between the plates 8 and 9.

The spring means consists of several helical springs 1 3 (only one of which is shown) with a soft characteristic and arranged on a partial circle. A single, centrally arranged spring can also be used. Apart from helical springs, other springs, for example plate springs, can be employed. The springs 13 rest in bores 14 (only one of which is shown) of the plate 8 and bear on the base of these bores 1 4 and on the adjacent face of the plate 9. The base of each bore 14 is bored through so that a connection is created from the stub pipe 2 to the gap s between the plates 8 and 9.

A further bore 15, which receives an assembly screw engaging into the plate 9, is present in the centre of the plate 8. The screw is inserted before the assembly of the plates 8 and 9 and tightened against the effect of the springs 1 3. In this state, the plates 8 and 9 can be inserted into the housing 1. The screw is removed after the insertion.

Radially outside the springs 13, the mutually adjacent faces of the plates 8 and 9 are provided with sealing rings 1 6 and 1 7 arranged opposite each other. On pressure loading of the plate 8, a sealing takes place by way of the sealing ring 11 of the plate 9 and the sealing ring 7 at the ring 5. On pressure loading of the plate 9, sealing-off takes place by way of the sealing rings 1 6 and 1 7 of the plates 8 and 9 as well as by way of the sealing ring 1 2 of the plate 8 and the sealing ring 6 at the ring 4.

The plates 8 and 9 interengage by way of centring means. This centring means can be formed by, for example, providing the plates 8 and 9 at their inside faces with grooves. A ring can be laid into the grooves which are in alignment each with the other. Preferably, however, the centring means consists-as il lustratedof a projection 1 8 which is provided at the inside face of the plate 8. The projection 18 engages into a recess 1 9 in the plate 9. A clearance fit exists between the projection 18 and the recess 1 9.

The diameter d2 of the projection 1 8 or of the recess 19 and the mean diameter dl of the sealing rings 1 6 and 1 7 are greater than the diameter d of the sealing rings 11 and 1 2. Preferably, the sealing rings 1 6 and 1 7 are arranged radially inwardly of the projection 18 or the recess 19. This arrangement entails advantages in respect of the construction and production of the plates. Without the manner of function changing, the sealing rings 1 6 and 1 7 can, however, be mounted radially outwardly of the projection 18 or the recess 19.

The valve operates in the following manner: If the pressure is present at the side of the stub pipe 2, then the plate 9-pressed forward onto its seat by the helical springs 1 3-is pressed by the pressure of the medium onto the sealing ring 7 so as to seal off the valve. Because of the bores 14 and 15, the plate 8 remains bearing against the sealing ring 6, since the pressure in the stub pipe 2 propagates through the bores 1 4 and 1 5 into the gap s between the plates 8 and 9.

On pressure loading from the side of the stub pipe 3, the plate 9 is lifted off by the pressure of the medium and the plates 8 and 9 are pressed together at the sealing rings 1 6 and 1 7 and the plate 8 against the sealing ring 6. The valve now seals off from the exit side at the sealing ring 6 as well as at the sealing ring 1 2 of the plate 8. The gap s is redisposed between the sealing ring 11 of the loaded plate 9 and the sealing ring 7. A connection is once again present by way of this gap s between the interior of the housing and the entry side of the pressure.

The last described case occurs in the described manner always when a pressure difference of certain level is present between the entry side and the exit side of the valve so that the forces acting on the plate 9 clearly exceed the forces acting on the opposite side.

If the pressure force acting on the surface with the diameter d due to the pressure at the entry side is equal to or only slightly greater than the sum of the oppositely directed forces due to the force of the helical springs 1 3 and the pressure at the exit side acting on the surface with the diameter d, then the plate 9 initially likewise lifts off from its seat. Medium flows into the housing 1 by way of the gap forming between the sealing rings 7 and 11 and there builds up the pressure at the entry side. As a result, a pressure gradient arises between the housing 1 and the exit on the side of the stub pipe 2, whereby the medium from the housing 1 flows by way of the centring means of the plates 8 and 9 and then through the bores 1 4 and 1 5 in the plate 8 towards the exit side in the stub pipe 2.

Since the centring means has a clearance fit between the projection 1 8 and the recess 19, which is so chosen that a pronounced throttle effect is provided, the pressure at the entry side can obtain in the housing 1 after a short transitional phase.

The diameter d2 of the centring means consisting of the projection 1 8 and the recess 1 9 is greater than the mean diameter d of the sealing rings 11 and 1 2. As a result, an additional annular surface, loaded by the pressure at the entry side, is present between the diameters d2 and d after the pressure buildup in the housing 1. Resulting from this is an additional force which is directed opposite to the spring force and the force of the pressure at the exit side now acting on the surface with the diameter d2. Due to this additional force, the plate 9 is moved towards the plate 8 and the valve seals off by way of the sealing rings 1 6 and 1 7 as well as by way of the sealing ring 1 2 of the plate 8. In order to ensure that the system remains stable in the now assumed setting, the force due to the pressure at the entry side now acting on the surface with the diameter dl is greater than the spring force, the additional spring force and the pressure force due to the pressure at the exit side acting on the surface with the diameter dl. To ensure this, the mean diameter dl of the sealing rings 16 and 17 differs only slightly from the diameter d2 of the projection 18 or of the recess 19.

Claims

1. A valve comprising a housing defining a flow duct and two parallel valve plates movably arranged in the duct and resiliently biassed away from each other to be spaced apart in an unloaded state thereof, one of the plates being provided with a passage therethrough from one major face to the other and each of the plates being provided with respective centring means engaging the centring means of the other plate with an annular clearance therebetween and further provided with a first sealing ring co-operable with the first sealing ring of the other plate and a second sealing ring co-operable with a respective third sealing ring which is arranged in the housing and has a diameter smaller than that of each first ring and of the annular clearance.

2. A valve as claimed in claim 1, wherein the diameter of the annular clearance is substantially equal to a diameter of each first sealing ring.

3. A valve as claimed in either claim 1 or claim 2, wherein the diameter of the annular clearance is greater than the mean diameter of each first sealing ring.

4. A valve as claimed in any one of the preceding claims, wherein the plates are resiliently biassed by spring means having a flat spring characteristic.

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