GB2203517A

GB2203517A - Valve for fluids

Info

Publication number: GB2203517A
Application number: GB08705124A
Authority: GB
Inventors: John Dewar
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-03-05
Filing date: 1987-03-05
Publication date: 1988-10-19
Also published as: GB8705124D0

Abstract

A valve has a housing (10), guide means (15) in the housing which operates to provide guidance in an upright direction when the valve is in use, a first valve member (19) reciprocally slidable over and guided by the guide means, means (preferably a counterweight system 23, 24, 25) biassing the first valve member upwards for sealing engagement under predetermined pressure beneath a valve aperture (14) in the housing, and a second valve member (27) slidably mounted and reciprocatable in an upright direction on the first valve member for sealing engagement under predetermined pressure above a valve aperture (30) in the first valve member. Preferably the valve is used in a sealed storage tank containing a liquid blanketted with nitrogen. In order to avoid tank-damaging extremes of pressure when the tank is refilled, nitrogen is vented as the liquid enters, while if the nitrogen system fails as liquid is withdrawn, air is admitted. <IMAGE>

Description

TITLE: Valve for Fluids This invention is concerned with a valve for fluids.

Sealed storage tanks are employed to contain liquids for use in some industrial processes, the liquid in a tank being blanketed with nitrogen via a reducing and control valve set. If excessively high or low pressure conditions occur in the tank, structural damage may result. When the tank is refilled, in order to avoid excessively high pressure in the tank, nitrogen is vented as the liquid enters. If the nitrogen system fails or cannot cope with emergency requirements as liquid is withdrawn, air is admitted to the tank to avoid excessively low pressure in the tank.

It is an object of the present invention to provide a valve of simple and reliable construction for preventing excessively high and low pressure conditions in sealed liquid storage tanks. The valve may of course have other applications.

According to the invention, there is provided a valve for fluids comprising a housing, guide means in the housing, which guide means operate to provide guidance in an upright direction when the valve is in use, a first valve member reciprocably slidable over and guided by the guide means, means biassing the first valve member upwards for sealing engagement under predetermined pressure beneath a valve aperture in the housing, and a second valve member slidably mounted and reciprocable in an upright direction on the first valve member for sealing engagement under predetermined pressure above a valve aperture in the first valve member.

The guide means preferably comprise a guide spindle centrally mounted in the housing. The first valve member then preferably comprises a tubular portion disposed around said spindle and a lower disc-like portion engageable beneath the valve aperture in the housing.

The second valve member may then suitably comprise a tubular portion disposed around the tubular portion of the first valve member and a lower disc-like portion engageable above a valve aperture in the disc-like portion of the first valve member. The tubular portion of the second valve member may at its upper end fit into an annular damper shroud carried by the tubular portion of the first valve member.

The aforesaid biassing means preferably comprise counterweights disposed in the housing and connected to the first valve member by cords running round pulleys.

Desirably, the second valve member engages when under its own weight above the valve aperture in the first valve member.

The following is a description, by way of example, of an embodiment of a valve in accordance with the invention, reference being made to the accompanying schematic drawings, in which, Fig. 1 is a sectional view of the valve with both valve members in closed positions, Fig. 2 is a sectional view of the valve with its first valve member in an open position, and Fig. 3 is a sectional view of the valve with its second valve member in an open position.

The valve comprises a generally tubular housing 10 having upper and lower annular flanges 11, 12 around apertures 13, 14 for the passage of air or nitrogen. A central, vertical guide spindle 15 extends co-axially through the housing 10 between a top support arm 16 carried by the flange 11 and a bottom support arm 17 carried by pillars 18 depending from the flange 12.

Slidably mounted on the spindle 15 is a first valve member 19 comprising a tubular portion 20 and a lower disc-like plate 21. Near the top of the tubular portion 20, the first valve member has a damper shroud 22 in the form of a depending annular flange. Cords 23 are connected to the upper part of the valve member 19, pass round pulleys 24 carried by the arm 16, and are fastened to counterweights 25. The counterweights urge the first valve member 19 upwards so that the plate 21 engages with the underside of the flange 12 and seals the aperture 14.

An annular sealing member 26 ensures a suitable seal. A second valve member 27 is slidably mounted on the tubular portion 20, this second valve member comprising a tubular "deadweight", portion 28 and a lower disc-like plate 29.

The weight of the second valve member 27 causes the plate 29 to bear on the top of the plate 21 and close apertures 30 therein. Sealing is ensured by sealing rings 21 in the plate 21.

As shown in Fig. 1, under normal conditions the plate 29, is seated by gravity and the plate 21 is seated by the action of the counterweights so that apertures 14 and 30 are sealed.

Under low-pressure conditions in a tank to which the valve is fitted, both valve members 19 and 27 move downwards, as shown in Fig. 2, to an extent determined by the flow/pressure drop relationship so that air can enter the tank through the aperture 14. As flow increases the valve travel will increase but with minimal pressure drop increment, i.e. the valve is virtually free from pressure rise once the opening set point is reached. As flow decreases the valve will progressively close until seating occurs.

Under high-pressure conditons in the tank, the second valve member 27 lifts at the appropriate set point to open the apertures 30 as shown in Fig. 3. The first valve member 19 remains stationary.

The upper end of the tubular portion 28 is slidably received in the damper shroud 22 to aid clean reseating with minimum chatter.

The valve is generally insensitive to outside conditions but should be kept free from dirt or water which may influence free operation or the set points for movement of the valve members.

The valve can readily be modified so that each valve member opens at any desired set point within a wide range of values.

The different parts of the valve can be made from any suitable materials. Examples of suitable materials are polypropylene for the housing 10, stainless steel for the guide spindle 15, polyvinylchloride for the plate 21 and shroud 22, stainless steel for the plate 29, zincplated mild steel for the counterweights, polypropylene for the pulleys and terylene for the cords.

Claims

1. A valve for fluids including: a housing; guide means in the housing, which guide means operates to provide guidance in an upright direction when the valve is in use; a first valve member reciprocally slidable over and guided by the guide means; means biassing the first valve member upwards for sealing engagement under predetermined pressure beneath a valve aperture in the housing; and a second valve member slidably mounted and reciprocatable in an upright direction on the first valve member for sealing engagement under predetermined pressure above a valve aperture in the first valve member.

2. A valve as claimed in Claim 1, wherein the guide means comprises a guide spindle centrally mounted in the housing.

3. A valve as claimed in Claim 2, wherein the first valve member comprises a tubular portion disposed around said spindle and a lower disc-like portion engageable beneath the valve aperture in the housing.

4. A valve as claimed in Claim 3, wherein the second valve member comprises a tubular portion disposed around the tubular portion of the first valve member and a lower disc-like portion engageable above a valve aperture in the disc-like portion of the first valve member.

5. A valve as claimed in Claim 4, wherein the tubular portion of the second valve member at its upper end fits into an annular damper shroud carried by the tubular portion of the first valve member.

6. A valve as claimed in any of the preceding Claims, wherein the biassing means comprises counterweights disposed in the housing and connected to the first valve member by cords running round pulleys.

7. A valve as claimed in any of the preceding Claims, wherein the second valve member engages when under its own weight above the valve aperture in the first valve member.

8. A valve for fluids as claimed in any of the preceding Claims and substantially as described hereinbefore.