GB2549715A

GB2549715A - A Residual pressure device

Info

Publication number: GB2549715A
Application number: GB1607135.9A
Authority: GB
Inventors: William Birch David
Original assignee: Cylvabirch Ltd
Current assignee: Cylvabirch Ltd
Priority date: 2016-04-25
Filing date: 2016-04-25
Publication date: 2017-11-01
Anticipated expiration: 2036-04-25
Also published as: GB2549715B

Abstract

A residual pressure device has an inlet 4 a side chamber inlet 13 and outlet 3. Gases within said valve may communicate via flow passage 2. In a closed position (Fig 2) shuttle 9 is biased toward the outlet or downstream end of said valve, via spring 11 and sealing means 5 which may be an O ring which may contact sealing face 14. A sleeve 35 is disposed around the shuttle and contacts the valve body via an angled face 40. Figures 3 and 4 disclose the valve partially open and fully open. Incoming gas pressure biases the shuttle toward the inlet. The sleeve is constrained by abutment member 39 and biased by resilient member 37. The sleeve protects sealing member 5 preventing gas flow from damaging or lifting it from its seat on the shuttle. Figure 5 discloses a filling member 50 pushing the shuttle fully back.

Description

A Residual Pressure Device

The present invention relates to a residual pressure device (RPD). In particular, the present invention relates to an RPD for use in valves attached to cylinders containing pressurised fluid and more specifically, pressurised gas. RPDs are well known in the packaged compressed gas industry. They are typically employed in valves or pressure regulators to prevent backflow of contaminants into the gas cylinder in the event that a user leaves the main shut-off valve open. An RPD is typically located in the outlet channel of the valve, downstream of the main shut-off valve. However, the RPD may be located anywhere in a valve or regulator. In some cases the RPD may serve as a pressure regulator, for example, the RPD may function as a step down pressure regulator.

Examples of prior art RPD designs are shown in Figures 1A and 1B.

For the sake of clarity, throughout this document the terms “upstream” and “downstream” are used consistently to refer to the respective upstream and downstream ends of the RPD with respect to outflowing gas during normal operating conditions. Normal operating conditions being when gas flows through the RPD from a gas cylinder towards a downstream process or device.

Referring to Figure 1A, a prior art RPD 1 comprises a flow passage 2 having a downstream, or outlet, end 3, and an upstream end 4. A side flow passage 13 connects the flow passage 2 with the outlet of the main shut-off valve (not shown) of a pressurised gas cylinder (not shown). A shuttle 6 is located in the flow passage 2. The shuttle 6 is of substantially tubular form having an inner passage 22 which provides fluidic communication between the downstream, or outlet, end 3 of the flow passage 2 and the upstream end 4 of the flow passage 2. The shuttle 6 is biased in the direction of the downstream end 3 of the flow passage 2 by a resilient spring 11. The shuttle 6 carries a sealing o-ring 5 located in a groove 7 substantially at a downstream end 9 of the shuttle 6. In this example, a flow channel 8 is provided in the downstream end 9 of the shuttle 6 to ameliorate gas flow and add encastre support to the shuttle 6 by means of radial guide vanes 12 when the RPD is open.

The upstream end 10 of the shuttle comprises a flange portion 15 which carries a second sealing o-ring 16 in a groove 17 on its peripheral edge. The second seal 16 engages with a peripheral wall 31 of the flow passage 2 to seal the upstream end 4 of the flow passage 2. A chamber 18 is thus formed between the flange 15 of the shuttle 6 and the downstream wall 19 of the flow passage 2.

In use, when closed, the shuttle 6 is pushed towards the downstream end 3 of the flow passage 2 by the resilient spring 11. A pressure PI exists at the downstream, or outlet, end 3 of the flow passage 2. The pressure PI is in communication with the upstream end 4 of the flow passage 2 via the inner passage 22. This pressure acts on a first face 21 of the flange 15 resulting in a force FI acting on the shuttle 6 in the direction of the downstream end 3.

As a result of the spring force from resilient spring 11 and the force FI acting on the shuttle 6, the seal 5 is pushed into sealing engagement with a valve seat 14 and hence seals the open downstream end 3 of the flow passage from the chamber 18.

It has been found in practice that the o-ring seal 5 of the prior art RPD 1 can suffer damage to, or total loss of, the seal 5. This is typically as a result of the low temperature environment caused by gas flowing over the seal 5 at high speed and with high differential pressure. Low temperatures cause the rubber compound of the seal 5 to become brittle. This causes the seal 5 to become vulnerable to disintegration when buffeted by high gas flow speeds, or when hit by particles such as solid carbon dioxide.

In addition, loss of the seal 5 can occur during both filling and withdrawal of gas. During filling, the shuttle 6 is pushed back mechanically against both the action of the resilient spring 11 and the closure force generated on the first face 21 of the flange 15 by the filling pressure. This leaves the seal 5 in a high speed gas flow which can result in it being lifted out of its groove 7 by aerodynamic suction. It may then break up and pass into the cylinder with the gas. During withdrawal of gas, the seal 5 may be subjected to extremely high flow rates which can, again, cause it to be lifted out of its groove 7 and pass into downstream pipework and processes.

Figure 1B shows an alternative prior art design 25 of an RPD in which a fixed sleeve 20 is provided. For clarity, like numerals have be used to reference like components. The sleeve 20 covers a portion of the seal 5 leaving only a small amount free to seal against the valve seat 14. This design seeks to reduce the surface area of the seal 5 as much as possible to increase the surface pressure of the seal and reduce hysteresis of the RPD in responding to changing flow draw-off in use. However, this design does not fully mitigate against the risk of damage to, or loss of, the seal 5 which may still be compromised as a portion of it is still exposed to low temperatures and aerodynamic loads, all be it to a reduced extent.

The present invention provides a residual pressure device comprising: a flow passage having a downstream end and an upstream end, wherein a valve seat is located substantially at the downstream end of the flow passage; a shuttle moveably located within the flow passage and biased towards the downstream end of the flow passage by a first resilient member, wherein the shuttle carries a sealing member arranged, in use, to sealingly engage with the valve seat when the residual pressure device is in a closed position; and a sleeve located in the flow passage, characterised in that the sealing member is moveable with respect to the sleeve, so that, in use, the sleeve at least partially covers the sealing member when the residual pressure device is in an open position.

The present invention is advantageous as the seal is able to move with respect to the sleeve so that the amount of the seal which is covered, and therefore protected, by the sleeve may vary. Preferably, the sleeve substantially covers the sealing member when the residual pressure device is in an open position to provide maximum protection.

In a preferred example, the sleeve is moveable with respect to the flow passage so that it may move out of the flow path of the gas when the valve is open. The sleeve is preferably mounted on the shuttle.

Preferably relative movement between the sleeve and the shuttle is constrained by an abutment member to limit the movement of the sleeve with respect to the shuttle and better control sleeve position.

In one preferred example the sleeve comprises a channel within which the abutment member is received, wherein the dimensions of the channel define the extent to which the sleeve is able to move with respect to the shuttle. Preferably the abutment member is located on the shuttle.

The sleeve is preferably biased towards the downstream end of the flow passage by a second resilient member which may be a wave washer or any other suitable resilient member. Preferably the second resilient member is located between an upstream end of the sleeve and a flange located at an upstream end of the shuttle. The upstream end of the sleeve may preferably comprise a flange.

The downstream end of the sleeve is preferably profiled to match the profile of a downstream end wall of the flow passage to provide secure engagement when the RPD is closed. The downstream end of the sleeve is preferably tapered to match a tapered downstream wall of the flow passage.

In one preferred example the downstream end of the sleeve comprises at least one flow channel to ameliorate gas flow out of the RPD.

The present invention also provides a valve assembly for a pressurised gas cylinder comprising a shut off valve and a residual pressure device as described above.

The present invention further provides a regulator assembly comprising a residual pressure device as described above.

The present invention still further provides a gas supply assembly comprising: a gas cylinder; and a valve assembly or a regulator assembly as described above.

Examples of the present invention will now be described with reference to the following drawings in which:

Figure 1A shows a schematic view of prior art RPD design;

Figure 1B shows a schematic view of an alternative prior art design;

Figure 2 shows a schematic view of an RPD in accordance with the present invention in the closed position;

Figure 3 shows a schematic view of the RPD of Figure 2 in an open, low flow, position;

Figure 4 shows a schematic view of the RPD of Figure 2 in an open, high flow, position; and

Figure 5 shows a schematic view of the RPD of Figure 2 in a filling position. For clarity, like numerals are used throughout to reference like components.

Referring to Figure 2, an RPD 30 comprises a flow passage 2 having a downstream, or outlet, end 3 and an upstream end 4. A shuttle 6 is moveably located in the flow passage 2 and biased towards the downstream end 3 of the outlet passage by a resilient biasing member 11. In this example the resilient biasing member 11 is a helical spring. However, any other suitable type of resilient member may be used. A side flow passage 13 connects the flow passage 2 to a supply of pressurised fluid. Typically the side flow passage 13 is connected to the outlet of the main shut off valve (not shown) of a gas cylinder located upstream of the RPD.

The shuttle 6 is substantially of tubular form having an inner passage 22, a downstream end 9, and an upstream end 10. The upstream end 10 of the shuttle 6 comprises a flange portion 15 which substantially conforms to the outer longitudinal wall 31 of the flow passage 2. The outer periphery of the flange portion 15 is sealed against the wall 31 by a seal 16 which is carried in a groove 17 located on the outer periphery of the flange portion 15. A chamber 18 is thus formed between the flange 15 of the shuttle 6 and a downstream wall 19 of the flow passage 2. A seal 5 is located substantially at the downstream end 9 of the shuttle 6. The seal 5 is carried in a groove 7 located on the shuttle 6. The downstream end of the shuttle 6 further comprises flow channel 8 to ameliorate gas flow when the RPD is open and add encastre support to the shuttle 6 by means of radial guide vanes 12. A sleeve 35 is moveably mounted on the shuttle 6. The sleeve 35 comprises a flanged upstream portion 36 and a tapered downstream portion 40. The taper of the downstream portion 40 conforms with the taper of the downstream wall 19 of the flow passage 2. The sleeve 35 further comprises a channel 38 which is arranged to receive an abutment member 39 fixedly located on the shuttle 6. As will be described further below, the abutment member 39 serves to restrict how far the sleeve 35 is able to move with respect to the shuttle 6. A wave washer 37 is located between the flange portion 36 of the sleeve 35 and the flange portion 15 of the shuttle 6. The wave washer 37 biases the sleeve 35 towards the downstream end 3 of the flow passage 2. Although a wave washer is described here with reference to RPD 30, it will be clear to the skilled person that any suitable resilient member may be used in place of a wave washer.

When the RPD 30 is closed as shown in Figure 2, there is a gas pressure PO in the chamber 18 which is less than or equal to the residual gas pressure. The pressure PO acts on a second face 42 of the flange portion 15 tending to push the shuttle 6 towards the upstream end 4 of the flow passage 2. As an aside, PO also acts on the downstream tapered end 40, and the upstream and downstream faces of the flange portion 36, of the sleeve 35. However, the resultant forces balance each other out so no further discussion of these forces is given here. A pressure PI exists at the downstream, or outlet, end 3 of the flow passage 2, and communicates with the upstream end 4 of the flow passage 2 via the inner passage 22 of the shuttle 6. The shuttle 6 is biased by the resilient spring 11 and force FI - resulting from the pressure PI acting on the first face 21 of the flange 15 - towards the downstream end 3 of the flow passage 2 such that the seal 5 sealingly engages with a valve seat 14 located substantially at the downstream end 3 of the flow passage 2. The sleeve 35 is biased towards the downstream wall 19 of the flow passage 2 by the wave washer 37 such that the tapered end 40 abuts the downstream wall 19. It should be understood that the reaction force of the wave spring 37 acting on the flange 15 of the shuttle 6 is negligible in comparison to the resultant force acting on the shuttle 6 from the resilient spring 11 and pressure force FI. The seal 5 is thus held in sealing engagement against the valve seat 14 when the RPD is in the closed position.

Referring now to Figure 3, in one example, gas is supplied to the chamber 18 via side flow passage 13 at first pressure P2 which is sufficient to open the RPD to a small extent to provide a low flow to the outlet of the RPD. The pressure P2 acts against the second face 42 of the shuttle flange portion 15 causing the shuttle 6 to be pushed in the direction of the upstream end 4 of the flow passage 2. A pressure P3 exists at the downstream, or outlet, end 3 of the flow passage 2. This pressure P3 communicates with the upstream end 4 of the flow passage 2 via inner passage 22 and acts on the first face 21 of the shuttle flange portion 15 resulting in a force F3 acting on the shuttle 6 and pushing it in the direction of the downstream end 3 of the flow passage. This force F3 together with the force from the resilient spring 11 tries to close the RPD. Provided that the pressure P2 is sufficiently high, and the pressure P3 sufficiently low, the overall force balance will cause the shuttle 6 to move towards the upstream end 4 of the flow passage 2 and the RPD will remain open.

As previously discussed, a flow channel, or channels, 8 may be provided in the downstream end 9 of the shuttle 6 to ameliorate the gas flow out of the RPD and provide encastre support to the shuttle by means of radial guide vanes 12, but this is not essential.

The wave washer 37, which is in compression, exerts a force on the flange portion 36 of the sleeve 35 towards the downstream end 3 of the flow passage 2 such that the sleeve 35 moves towards the downstream wall 19 of the flow passage 2. As the sleeve 35 moves towards the downstream wall 19, and the shuttle 6 moves towards the upstream end 4 of the flow passage 2, the sleeve 35 substantially covers the seal 5 and thus protects it from low temperature gas flows, buffeting forces and solid objects.

In one example, not shown, the force acting on the sleeve flange 36 may be such that the sleeve remains in contact with the downstream wall 19 of the flow passage 2. Since there is no seal provided at the downstream end 40 of the sleeve 35, gas is still able to flow past the end 40 of the sleeve 35 and out of the RPD. If desired, a flow passage, or passages, may be provided in the downstream portion 40 of the sleeve 35 to ameliorate the gas flow therepast.

Turning now to Figure 4, a second example is shown in which gas is supplied to the chamber 18 via side flow passage 13 at a second, higher, pressure P4. The pressure P4 is sufficient to open the RPD to its full extent to provide a high flow to the outlet of the RPD. In this example, the pressure P4 acts against the second face 42 of the shuttle flange portion 15 causing the shuttle 6 to be pushed in the direction of the upstream end 4 of the flow passage 2. A pressure P5 exists at the downstream, or outlet, end 3 of the flow passage 2. This pressure P5 communicates with the upstream end 4 of the flow passage 2 via inner passage 22 and acts on the first face 21 of the shuttle flange portion 15 resulting in a force F5 acting on the shuttle 6 and pushing it in the direction of the downstream end 3 of the flow passage. This force F5 together with the force from the resilient spring 11 tries to close the RPD. Provided that the pressure P4 is sufficiently high, and the pressure P5 sufficiently low, the overall force balance will cause the shuttle 6 to move towards the upstream end 4 of the flow passage 2 and the RPD will remain open.

The operating condition of the RPD depends on the pressure within chamber 18 and the pressure at the downstream, or outlet, end 3 of the flow passage 2. Each of these pressures are variable depending on the flow velocity and density of the fluid (among other things). A person skilled in the art of RPDs will be familiar with this force balance and no further explanation is required here.

The force of the wave washer 37 acting on the flange portion 36 of the sleeve 35 causes the sleeve 35 to move towards the downstream wall 19 of the flow passage 2. The relative movement between the shuttle 6 and sleeve 35 causes the seal 5 to be covered and protected by the sleeve 35.

To ensure sufficient flow area for the gas in the high flow condition, the sleeve 35 is restricted in the extent of its downstream movement by the abutment member 39 located on the shuttle 6. The abutment member 39 is received in a channel 38 in the sleeve 35. The longitudinal extent of the channel 38 allows for a fixed amount of relative movement between the sleeve 35 and shuttle 6. Once the sleeve 35 has moved a fixed distance, determined by the dimensions of the channel 38, along the shuttle, no further relative movement is possible as the abutment member 39 abuts the upstream side 44 of the channel 38.

Moving now to Figure 5, the RPD 30 of figure 2 is shown in a filling position. During filling, a filling connector 50 is inserted into the downstream end 3 of the flow passage 2 to depress the shuttle 6 against the resilient spring 11, and the filling pressure acting on the first face 21 of the shuttle flange portion 15, and hence push the seal 5 out of sealing engagement with the valve seat 14. As the shuttle 6 is pushed in the upstream direction towards the upstream end 4 of the flow passage 2, the wave washer 37 causes the sleeve 35 to move relatively to the shuttle 6 in the direction of the downstream wall 19 of the flow passage 2. The sleeve 35 continues to move relative to the shuttle 6, under the action of wave washer 37, until the upstream side 44 of the channel 38 comes into contact with the abutment member 39. The relative movement between the sleeve 35 and shuttle 6 causes the seal 5 to be covered and protected by the sleeve 35 during filling.

It may be that the abutment member 39 and channel 38 are not provided such that the sleeve 35 is able to move in an unconstrained manner along the shuttle 6. In this case, it may be desirable to provide a flow channel, or channels, in the downstream end 40 of the sleeve 35 to ameliorate the gas flow in the event that the sleeve 35 remains in contact with the wall 19 during high flow or filling conditions.

The example RPD described above with reference to Figures 2 to 5 is one example only of the invention. In other examples, not shown, it is envisaged that rather than being carried on the shuttle 6, the sleeve 35 may be moveably connected to the longitudinal wall 31 of the flow passage 2. For example, the flange portion 36 of the sleeve 35 may comprise a key feature which is slidingly engaged with a groove feature provided in the longitudinal wall 31.

In another alternative, the sleeve 35 may be fixed to the downstream wall 19 of the flow passage. In this example flow channels are provided in the downstream portion 40 of the sleeve 35 to allow for the passage of gas therethrough during flow and filling conditions.

Claims

Claims:

1. A residual pressure device comprising: a flow passage having a downstream end and an upstream end, wherein a valve seat is located substantially at the downstream end of the flow passage; a shuttle moveably located within the flow passage and biased towards the downstream end of the flow passage by a first resilient member, wherein the shuttle carries a sealing member arranged, in use, to sealingly engage with the valve seat when the residual pressure device is in a closed position; and a sleeve located in the flow passage, characterised in that the sealing member is moveable with respect to the sleeve, so that, in use, the sleeve at least partially covers the sealing member when the residual pressure device is in an open position.

2. A residual pressure device as claimed in claim 1, wherein the sleeve is moveable with respect to the flow passage.

3. A residual pressure device as claimed in claim 2, wherein the sleeve is mounted on the shuttle.

4. A residual pressure device as claimed in claim 2 or claim 3, wherein relative movement between the sleeve and the shuttle is constrained by an abutment member.

5. A residual pressure device as claimed in claim 4, wherein the sleeve comprises a channel within which the abutment member is received, wherein the dimensions of the channel define the extent to which the sleeve is able to move with respect to the shuttle.

6. A residual pressure device as claimed in claim 4 or claim 5, wherein the abutment member is located on the shuttle.

7. A residual pressure device as claimed in any one of claims 2 to 6, wherein the sleeve is biased towards the downstream end of the flow passage by a second resilient member.

8. A residual pressure device as claimed in claim 7, wherein the second resilient member is a wave washer.

9. A residual pressure device as claimed in claim 7 or claim 8, wherein the second resilient member is located between an upstream end of the sleeve and a flange located at an upstream end of the shuttle.

10. A residual pressure device as claimed in claim 9, wherein the upstream end of the sleeve comprises a flange.

11. A residual pressure device as claimed in any one of claims 2 to 10, wherein a downstream end of the sleeve is profiled to match the profile of a downstream end wall of the flow passage.

12. A residual pressure device as claimed in claim 11, wherein the downstream end of the sleeve is tapered.

13. A residual pressure device as claimed in any preceding claim, wherein a downstream end of the sleeve comprises at least one flow channel.

14. A valve assembly for a pressurised gas cylinder comprising a shut off valve and a residual pressure device according to any of the preceding claims.

15. A regulator assembly comprising a residual pressure device according to any of the preceding claims.

16. A gas supply assembly comprising: a gas cylinder; and a valve assembly according to claim 12, or a regulator assembly according to claim 13.