GB2041497A - Gate valve - Google Patents

Abstract

A gate valve for fluids comprises a closure element 5 consisting of two valve discs 6 and 7 and a chamber 16 therebetween of alterable volume which is charged with a pressure medium in order to press the discs against seats 3 and 4. To open the valve, the valve discs are retracted towards each other away from the seats and the closure member 5 is displaced sideways by an arm 11. In order that relatively high closing forces can be generated with low medium pressure, a second chamber 33 comprising plates 34 and 35 connected by a bellows 36 is disposed in the chamber 16. Plate 34 is rigidly connected by rods 37 to the non-adjacent valve disc 7, and plate 35 is connected similarly to valve disc 6 by rods 38. The force acting on each valve disc due to pressure medium in the chamber 16 is thus increased by the force acting in the same direction on the connected plate. <IMAGE>

Description

SPECIFICATION A gate valve The invention relates to a gate valve (stop slide valve) which includes a closure element consisting of two valve discs and a chamber arranged therebetween of alterable volume in order to change the distance between the discs.

In gate valves of this type (e.g. known from German Offenlegungschrift 20 52 488) the closure element can be displaced, pivoted or rolled sideways between an open position and a closed position whilst the discs are sufficiently close together so that such movement of the closure element is not impeded. In order to close a gate valve of this type the closure element is brought into a position in front of the opening or openings to be closed. The chamber located between the discs is than charged with a pressure medium, as a rule compressed air, whereupon the discs move outwardly. Both discs may, as in German Offenlegungsschrift 20 52 488, be provided with gaskets. A valve seat surrounding the openings to be closed co-operates with each of these gaskets. In the case where only one opening is to be closed, the second disc simply has a supporting function.

As a rule the two discs are spring loaded, and accordingly the distance between the discs decreases when the pressure in the chamber is released.

In order to initiate the opening of the gate valve, the discs must move in such a way that the closure element can move sideways again in an unobstructed manner.

A disadvantage of the known gate valves of this type is that a great deal of energy has to be expended to produce a sufficiently high pressure in the pressure medium, particularly if the openings that are to be closed have a relatively large diameter compared to the chamber itself and if a high closing pressure is to be generated. If, for example, in the case of pneumatically actuated gate valves the necessary pressure medium operating pressure exceeds 10 Atmospheres, expensive postcompressors are necessary in addition to the normal compressors. Also in the case of hydraulic actuation, which in any case is preferably not used for gate valves in vacuum applications on account of the hydraulic oil the expenditure for the compressors rises considerably with increasing blank-off pressure (final pressure).

The object of the present invention is to provide a gate valve of the aforementioned type in which relatively high closing forces can be generated with low pressure medium pressures.

This objective is achieved in accordance with the invention by providing a gate valve which includes a closure element consisting of two valve discs and a chamber arranged therebetween of alterable volume in order to change the distance between the discs, wherein a further chamber of alterable volume is disposed in the (first) chamber between the valve discs and comprises two plates substantially parallel to the valve discs, and each plate is connected to the valve disc furthest away from it.

If in the case of a gate valve designed in this manner an elevated pressure is produced in the space formed by the two chambers, this pressure first of all acts in a known manner in such a way that the valve discs are forced outwardly. In addition this pressure acts on the plates of the second chamber in such a way that these plates move towards one another. The force acting on a valve disc thus has the same direction as the force acting on the in each case non-adjacent plate of the further (inner) chamber. In accordance with the invention, these two elements are joined together so that overall the effective area is enlarged and thus the forces acting on the valve discs are increased. Depending on the size of the plates, the forces can be magnified by almost a factor of two without increasing the pressure medium pressure.

Further advantages and details of the invention will now be described in more detail with reference to the accompanying drawing which is a diagrammatic cross-sectional elevation of an embodiment of a gate valve according to the invention. The drawing shows only those parts of the embodiment essential for the invention.

Referring to the drawing, the gate valve is shown in the closed position, and comprises a housing of which only two side walls 1 and 2 with their respective openings 3 and 4 being partially illustrated. A closure element 5 includes valve discs 6 and 7 associated with the openings 3 and 4, the discs 6 and 7 having seals 8 and 9 on their periphery. In the closed position as illustrated, the seals 8 and 9 lie tight against the side walls 1 and 2 in the region of the periphery of the openings 3 and 4, and provide a tight seal for these openings.

The seals 8 and 9 as well as the associated seats may be formed in any desired manner depending on requirements, and they are therefore illustrated in a highly diagrammatic manner. If only one of the openings 3 or 4 is to be tightly closed, it is preferred to provide a seal only for that opening, and a simple supporting means on the opposite side.

In the embodiment illustrated the closure element 5 is mounted on an arm 11 by means of which it can be brought into the open position (not shown) and retracted An annular plate 1 2 which has a connecting member 1 3 with a flange and is thereby secured to the arm 11 and serves to retain the individual elements of the closure element 5 on the said arm 11.

In order to form a (first) chamber 1 6 between the two discs 6 and 7, further annular plates 1 7 to 20 are secured to the annular plat 1 2 and also to the valve discs 6 and 7.

Pairs of sealing rings 21 to 24 are provided in each case to ensure a sufficient degree of fluid tightness. Two concentric bellows 25, 26, and 27, 28 are provided in each case between the pairs of annular discs 17, 1 8 and 19, 20. The bellows 25, 26 and 27, 28 are of different diameters, and thus form annular chambers 29 and 30 which communicate with the atmosphere via a channel 31 in the arm 11.

The choice of two bellows for the chamber 1 6 is on grounds of safety and stability, and in many cases one pair of bellows is perfectly sufficient.

A further (second) chamber 33 formed by two plates 34 and 35 parallel to the valve discs 6 and 7 and by a bellows 36 is arranged within the chamber 1 6. One plate 34 is rigidly connected to the valve disc 7 of the outer chamber 1 6 by a plurality of rods 37 (only one of which is visible) secured to its periphery. The other plate 35 is rigidly connected in a corresponding manner to the valve disc 6 by means of a plurality of rods 38. The chamber 1 6 can be charged with compressed air via a channel 40 provided in the arm 11.

A flexible hose 41 communicating with a channel 42 in the arm 11 is connected to the chamber 33. By means of this channel 42 the chamber 33 can either be ventilated or charged with compressed air.

In the closed position as illustrated the chamber 1 6 is under pressure. The chamber 33 must be ventilated via the channel 42.

The pressure medium in the chamber 1 6 then acts on the valve discs 6 and 7 in the direction of the arrows. The pressure medium also acts on the plates 34 and 35 in the direction of the arrows 47 and 48, and thus likwise in the closing direction since the plate 34 is connected to the disc 7 and the plate 35 is connected to the disc 6. The external areas formed by the plates 34 and 35 thus represent an overall increase in effective area.

In order to initiate the opening procedure it is first of all necessary for the valve discs 6 and 7 to be retracted clear of the side walls 1 and 2. To this end, the pressure in the chamber 1 6 is first of all released or the chamber is ventilated, and the chamber 33 is charged with compressed air so that a force is exerted on the plates 34 and 35 which counteracts the closing force. The result is that the distance between the discs 6 and 7 decreases and the discs adopt the positions 6' and 7' shown by the dashed lines. The whole closure element 5 can then be swivelled by means of the arm 11.

In order to eliminate dirt and dust and limit and guide the aforedescribed retracting movement of the valve discs 6 and 7, a cylinder 50 whose axis is substantially normal to the discs 6 and 7 is mounted on the annular plate 12, and short cylinders 51 and 52 of somewhat larger diameter are mounted on the discs 6 and 7 respectively. The cylinders 51 and 52 more or less overlap the cylinder 50, depending on whether the closure element is in its open position or in its closed position, and accordingly the expansion movement of the discs is in each case guided. The length of the cylinder 50 also determines the distance between the discs 6 and 7 in their open position, since the edges of the cylinder 50 in this position rest against the discs 6 and 7.

A further basic advantage of a gate valve according to the invention is that return springs for the valve discs 6 and 7 can be dispensed with and thus the gate valve can be actuated exclusively by means of compressed air. Return springs are not only disadvantageous since they represent additional structural parts; the force exerted by them also acts against the closing force, with the result that the pressure in the chamber must be higher, to compensate for the spring forces, than is necessary simply in order to produce the closing pressure. If it were desired to dispense with return springs in a gate valve of conventional design, an evacuation device for the chamber situated between the valve discs would have to be provided for the retracting movement of the discs.Such an evacuation device can be dispensed with in the gate valve according to the invention, i.e. it can be actuated and controlled exclusively by means of compressed air. In order to generate the closing force, the chamber 1 6 is charged with compressed air while the chamber 33 is ventilated. In order to generate the retracting movement, the pressure in the chamber 1 6 is released or the chamber is ventilated, and the chamber 33 is charged with compressed air, which causes the valve discs 6 and 7 to be retracted from their seating.

Overall, approximately a doubling of the force (or also a pressure reduction) compared with conventional bellow-type valves, lift cylinder, tensioning systems, etc., can be achieved with a gate valve according to the invention, and in fact without increasing the structural dimensions. Release springs, which require additional compression forces, are not necessary. Devices for generating the pressure medium presure can also be dispensed with.

The gate valve according to the invention can thus be used in vacuum applications (preferably with a gaseous pressure medium) as well as in hydraulic or pneumatic applications.

Claims (8)

1. A gate valve which includes a closure element consisting of two valve discs and a chamber arranged therebetween of alterable volume in order to change the distance between the discs, wherein a further chamber of alterable volume is disposed in the (first) chamber between the valve discs and comprises two plates substantially parallel to the valve discs, and each plate is connected to the valve disc furthest away from it.

2. A gate valve according to Claim 1, wherein the futher chamber is arranged to be charged at atmospheric pressure or if desired at elevated pressure.

3. A gate valve according to Claim 1 or 2, wherein the further chamber is formed by the plates and a bellows arranged therebetween.

4. A gate valve according to any one of the preceding claims, characterised in that the closure element includes an annular plate located between the valve discs, and in order to form the first chamber at least one bellows is provided between the annular plate and each valve disc.

5. A gate valve according to Claim 4, wherein an actuating arm for displacing the closure element is secured to the annular plate and supply channels for the two chambers are provided in the actuating arm.

6. A gate valve according to claim 4 or 5, wherein two concentric bellows are provided between the annular plate and each valve disc and the annular space formed thereby communicate with the atmosphere.

7. A gate valve according to any one of Claims 4 to 6, wherein a cylinder whose axis is substantially perpendicular to the valve discs is secured to the annular plate, and further cylinders secured to the valve discs cooperate with the first-mentioned cylinder to guide and limit the movement of the valve discs.

8. A gate valve substantially as hereinbefore described with reference to the accompanying drawings.