GB2139326A

GB2139326A - Safety valve

Info

Publication number: GB2139326A
Application number: GB08410235A
Authority: GB
Inventors: Kenneth Ian Dutfield Dean
Original assignee: Compair Power Tools Ltd
Current assignee: Compair Power Tools Ltd
Priority date: 1983-05-05
Filing date: 1984-04-19
Publication date: 1984-11-07
Also published as: GB8410235D0; GB2139326B

Abstract

A safety valve comprises a housing 11 having an inlet 19 and an outlet 20. A valve member 12 within the housing is operable substantially to choose the inlet or the outlet. Two springs 13, 14 bias the valve member to a position in which a flow path from inlet to outlet is open. The valve member includes means 33 defining a restricted flow path. When flow through the valve in either direction exceeds a predetermined rate, the valve member moves to close off the inlet or outlet respectively but the restricted flow path allows a bleed from the valve. <IMAGE>

Description

SPECIFICATION Safety valve The invention relates to safety valves and more particularly but not exclusively to safety valves for incorporation into hoses or other lines through which compressed air flows.

It is usual in compressed air systems for a tool or other device to which compressed air is to be supplied to be connected to a source of compressed air by a hose. The source of compressed air may be a fixed or temporary outlet within a factory or other workplaces or sites. As a safety precaution, a safety valve is normally included in the hose and is often positioned adjacent to the end of the hose which is connected to the source of compressed air. Known safety valves have normally been operable to act in one direction only (the direction of flow of compressed air through the hose) and have been arranged so that if the flow of compressed air through the hose exceeds a certain pre-determined figure, the valve operates to close and prevent further flow of compressed air through the hose.

However, such known one way valves suffer from the disadvantage that if the hose becomes disconnected from the source of compressed air either during ordinary disconnection of the hose from the source of compressed air or in accidental disconnection, the residual internal air pressure within the hose may cause the hose to whip and this may cause injury to workers in the vicinity Because known safety valves are one way valves, they are not effective to seal the hose against air within the hose during such disconnection.

It is an object of the present invention to provide a safety valve which is a two way valve operating in either direction to seal the valve under certain conditions.

The invention provides a safety valve comprising a housing having an inlet and an outlet and a valve member within the housing operable substantially to close the inlet or the outlet, means being provided resiliently biasing the valve member to a position in which a flow path through the valve from the inlet to the outlet is open and the valve member including means defining a restricted flow path therethrough, the arrangement being such that when flow through the valve in either direction exceeds a predetermined rate the valve member moves from its said resiliently biased position to a position substantially closing off either the inlet or the outlet of the valve, while the restricted flow path defining means permits a bleed from the valve.

Two preferred embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a section through the valve; Figure 2 is a section along the lines A-A of Figure 1, and Figure 3 is a view similar to Figure 1 showing a modified embodiment.

Referring first to Figures 1 and 2, a safety valve 10 comprises a housing 11, a valve member 12 and two springs 13 and 14.

The housing 11 consists of two members 16, 1 7 which are screwed together to form the housing, an appropriate threaded connection being provided at 18. The housing has a central cylindrical portion having an inlet 1 9 at one end and an outlet 20 at the other end.

It will be appreciated that although the ends have been described at inlet and outlet respectively for convenience, the valve may be mounted in an air hose in either direction and either end may form the inlet or the outlet.

Reduced diameter threaded end portions 22, 23 of the housing provide threaded connections for connection of the safety valve into an air line or other device through which compressed air flows. Frusto-conical valve seats 24, 25 are formed in the housing at the inlet and outlet ends respectively.

The valve member 1 2 is a generally cylindrical member which is free floating within the housing 11. The valve member is symmetrical about a central transverse plane along which the section of Figure 2 is taken.

End portions 28, 29 of the valve member are frusto-conical in shape and are dimensioned to seat in the valve seats 24, 25 when the valve is moved to an appropriate position. The main cylindrical portion of the valve member is cut-away at 30 so that the central portion of the valve member is generally cruciform in shape. A stepped enlarged diameter portion 31 of the valve member 1 2 provides shoulders on either side of the central transverse plane of the valve member against which respective one end of the springs 13, 14 seat.

The other ends of the springs seat against respective ends walls of the housing.

The frusto-conical ends 28, 29 of the valve member have narrow slots 33 formed therein.

The purpose of the slots33 is to provide a restricted flow path through the ends of the valve member so that a bleed of air may pass through the valve even when one of the end portions 28, 29 is seated in respective valve seat 24, 25.

It will be appreciated from Figure 1 that the length of the valve member 1 2 in the axial direction of the valve is less than the distance between the valve seats 24, 25. The springs 13, 14 are of equal strength so that, in its rest position, as shown in Figure 1, the valve member 12 is not seated in either of valve seats 24, 25 and allows a relatively free flow of air through the valve 10. The cut-away portions 30 of the valve member 1 2 provide an air passage through the central portion of the valve around the enlarged diameter portion 31 of the valve member and the size of the cutaway portions define the size of this flow passage which therefore acts as a meter ing passage through the valve.

In operation of the valve, the rest position of the valve is as shown in Figure 1 and as described above. When air flows through the valve, there is a pressure drop across the metering passage described above and the pressure drop is related to the flow of air through the valve. The effect of the pressure drop is to create an imbalance of forces on the valve member and the valve member will therefore tend to move in the direction of the flow through the valve until the imbalance thereby created in the spring forces of springs 13, 14 balances the pressure forces.As flow through the valve increases, the valve mem ber continues to move in the direction of flow and when the flow rises above a predetermined value as described above, the pressure drop across the valve will predominate over the spring forces and cause the valve member to seat in one of the valve seats 24, 25 depending on the direction of flow. The proportions of the valve member and valve seat are so designed that when the flow rises above the predetermined valve, the further movement of the valve tends to cause an even greater pressure drop so that the valve tends to snap shut to a position in which it is seated in one of the valve seats 24, 25.

In either of these positions, flow through the valve is substantially impeded although the passages 33 allow a bleed of air from the valve.

It will be appreciated that the synmetrical design of the valve and equal strength of springs 13, 14 means that the valve acts with equal effect in either direction of flow through the valve. In use, the valve would normally be fitted to a compressed air hose line at the upstream end of the line adjacent to a source of compressed air. The valve would normally be downstream of a coupling connecting the hose to the source of compressed air and might be attached to part of such a coupling As described above, the valve will operate substantially to close up the hose in the event of excessive air flow in either direction through the valve. Thus, the valve will provide protection: a) In the event of a hose rupture downstream of the valve when the supply of air will be cut off thereby preventing hose whip and dangerous airblast from the ruptured end of the hose.The valve will also operate in this way in the event of excess demand at the user end of the hose caused by circumstances other than hose rupture.

b) In the event of an operator disconnecting the airline at the user end from an air tool or other device to which the airline is connected without first shutting off the pressure. The valve will then operate as described in a above.

c) In the event of an operator disconnecting the airline at the supply end by disconnecting the coupling without first shutting off supply and allowing residual air to bleed from the hose. In this situation, the residual air in the hose can cause hose whip and air blast which may cause injury to the operator disconnecting the hose. In this situation, the valve will operate in the reverse direction to that described in a and b above but with the same effect of shutting off the hose to prevent injury while allowing residual air in the hose to bleed from the valve as described above.

It will be appreciated that the two way valve described above may also be used in any situation where a one way safety valve is normally used. Thus, the valve might be used immediately upstream of a quick connect coupling which does not itself contain a safety valve feature. It will also be appreciated that the further advantage of the two way valve described above is that there is no incorrect flow direction and therefore the valve cannot be fitted into a airline the wrong way round.

The invention is not limited to the embodiment of the valve described above and various modifications may be made.

One such modification is shown in Figure 3. In Figure 3, like parts have the same reference numerals as in Figures 1 and 2 and it will be seen that the valve member 12, the springs 13, 14 and the overall shape of the housing 11 are exactly as in Figure 1. However, in Figure 3, the housing 11 is formed in in three portions 40, 41, 42 which are screwed together, threaded connections being provided at 43 and 44. The effect of this is that the central portion 41 is a simple cylindrical shape and this facilitates manufacture of the housing. It will be appreciated that the length of this central portion is important for satisfactory operation of the valve and it is easier to control the length of cylindrical portion 41 accurately than to control the length of the bore in housing portion 16 of Figure Further modifications may also be made.

For example, the valve might form part of a coupling for connecting a hose to a source of compressed air in which case one threaded end 22, 23 of the valve would be replaced by an appropriate coupling member.

Further, the valve might be fitted directly to a hose by replacing one threaded end with a hose tail piece.

Still further, the springs 13, 14 might be of dissimilar strength thus biasing the valve so that the flow at which the valve closes is different in the two directions ot flow through the valve.

Claims

1. A safety valve comprising a housing having an inlet and an outlet and a valve member within the housing operable substantially to close the inlet or the outlet, means being provided resiliently biasing the valve member to a position in which a flow path through the valve from the inlet to the outlet is open and the valve member including means defining a restricted flow path therethrough, the arrangement being such that when flow through the valve in either direction exceeds a predetermined rate the valve member moves from its said resiliently biased position to a position substantially closing off either the inlet or the outlet of the valve, while the restricted flow path defining means permits a bleed from the valve.

2. A valve as claimed in ciaim 1 in which the valve member includes two end portions, the end portions being arranged to seat, in use, in valve seats formed at the inlets and outlets of the valve.

3. A valve as claimed in Claim 2 in which the restricted flow path defining means comprises slots in the end portions of the valve member.

4. A valve as claimed in any one of the preceding claims in which the valve member is spring biased by two springs acting in opposite directions.

5. A valve as claimed in Claim 4 in which the valve member includes an enlarged central portion, one spring being located between said portion and an inlet end of the housing and the other spring being located between said portion and an outlet end of the housing.

6. A valve as claimed in Claim 4 or Claim 5 in which the two springs are of equal strength.

7. A valve as claimed in Claim 4 or Claim 5 in which the two springs are of unequal strength.

8. A valve as claimed in any one of the preceding claims in which the housing is generally cylindrical and formed in two parts threadedly connected together.

9. A valve as claimed in any one of claims 1 to 7 in which the housing is generally cylindrical and formed in three parts threadedly connected together.

10. A valve is claimed in any one of the preceding claims in which the housing comprises means for connecting the housing at either end within an air supply sytem.

11. A valve as claimed in Claim 10 in which the connector means of the housing are in the form of screwthreaded end portions.

1 2. A safety valve substantially as hereinbefore described with reference to and as shown in Figure 1 and 2 or Figure 3 of the accompanying drawings.