GB2398858A

GB2398858A - Fluid flow controller

Info

Publication number: GB2398858A
Application number: GB0404266A
Authority: GB
Inventors: Christopher John Wheater
Original assignee: IMI Watson Smith Ltd
Current assignee: IMI Watson Smith Ltd
Priority date: 2003-02-26
Filing date: 2004-02-26
Publication date: 2004-09-01
Anticipated expiration: 2024-02-26
Also published as: GB0404266D0; GB2398858B; GB0304302D0

Abstract

A flow controller 1 for fluid flow has an inlet 5 for connection to a source 2 of pressurised fluid, an outlet 6 for connection to a device 3to be supplied with fluid, and a flow restrictor 4 between the inlet and the outlet. A first pressure-responsive valve 7 controls fluid flow between the inlet 5 and the flow restrictor 4 and a second pressure-responsive valve 9 controls flow between the restrictor 4 and the outlet 6. The valves 7,9 operate in response to inlet or outlet pressure and opposing control pressure, which may be supplied from a different source 10 from the fluid whose flow is being controlled. As the valves 7,9 control the pressure on both sides of the flow restrictor, flow through it can be controlled precisely.

Description

FLUID FLOW CONTROLLER

This invention relates to a flow controller for controlling the flow of fluids, in particular gases.

There are many industrial applications, for example in the manufacture of semi-conductors, where gas from a pressure source needs to be supplied to a device at a controlled flow rate. A flow controller is used to provide the required flow rate, and must control the flow even when the fluid pressure at the source and the device varies, as this can of course affect the flow.

According to the present invention, a flow controller for fluid flow has an inlet for connection to a source of pressurised fluid, an outlet for connection to a device to be supplied with fluid, and a flow restrictor between the inlet and the outlet, with a first pressure-responsive valve controlling fluid flow between the inlet and the flow restrictor and a second pressure-responsive valve controlling flow between the restrictor and the outlet.

This arrangement has the advantage that the valves control the pressure on both sides of the flow restrictor, thus ensuring that flow through it is controlled precisely. It also has the advantage of simplicity of manufacture and operation.

Preferably the flow controller includes an inlet chamber between the first valve and the flow restrictor, and an outlet chamber between the flow restrictor and the second valve.

Each valve conveniently comprises a valve member operated by a diaphragm movable in response to differential pressure across it. The diaphragm of the first valve is responsive to pressure in the inlet chamber and opposing pressure in an inlet control chamber. Similarly, the diaphragm of the second valve is responsive to pressure in the outlet chamber and opposing pressure in an outlet control chamber. Thus, the pressure in the inlet and outlet control chambers is regulated, and acts on the valves to maintain the required pressure in the inlet and outlet chambers. Changing the pressures in the control chambers will provide different flow rates. The diaphragms also separate the control chambers from the inlet and outlet chambers, thus separating the control pressure from the controlled fluid flow. The control pressure can therefore be supplied from a different source from the fluid whose flow is being controlled. For example, the fluid whose flow is being controlled may be a gas including toxic elements, which is kept separate from the control pressure, which may simply be air.

Preferably each valve member is biased towards the diaphragm by a spring. This ensures that the valve member follows the movements of the diaphragm. Preferably each valve member comprises a poppet valve.

Alternatively, each valve member may comprise a spool valve.

Normally, the spool valve will also be spring-biased towards the diaphragm. It is however possible that with a spool valve, the diaphragm would be omitted, so that each spool valve operates in dependence on the pressure differential across it, between the inlet or outlet chambers and the respective inlet or outlet control chambers.

An embodiment of the invention is illustrated, by way of example only, in the accompanying drawings, in which: Figure 1 is a diagram showing schematically the operation of the flow controller according to the invention; and

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Figure 2 is a cross-section through the flow controller of Figure 1.

Figure 1 shows the principle of operation of a flow controller 1 according to the invention. In Figure 1, a fluid such as a gas is supplied from a pressure source 2, whose pressure is variable, to a device 3, where the pressure of the gas is also variable, through the flow controller 1. The flow controller 1 operates to control the flow of the gas, despite the varying pressures. The flow controller 1 has a flow restrictor 4 between an inlet 5 connected to the pressure source 2 and an outlet 6 connected to the device 3, with a first pressure-responsive valve 7 controlling fluid flow between the inlet 5 and the restrictor 4 by a first controlled fluid pressure source 8, and a second pressure- responsive valve 9 controlling fluid flow between the restrictor 4 and the outlet 6 by a second controlled fluid pressure source 10. The control of the fluid flow by the valves 7, 9 ensures that the pressures on each side of the restrictor 4 are controlled, thus ensuring that fluid flow through the restrictor 4 itself is controlled.

The flow controller 1 is shown in more detail in Figure 2. It has a housing 11 formed as two mirror image parts 12, 13, with the first valve 7 accommodated in the housing part 12 and the second valve 9 in the housing part 13. The housing part 12 has an axially-extending inlet 14 for connection to the pressure source 2 through a line 15. The inlet 14 continues as an axial passage 16 to a radial valve passage 17 housing the first valve 7, which controls flow from the inlet 14 to an inlet chamber 18. The inlet chamber 18 is sealed by a flexible diaphragm 19, whose periphery is held between an external surface of the housing part 12 and an auxiliary housing part 20. The housing part 20 defines, on the outer side of the diaphragm 19, an inlet control chamber 21, connected through a passage 22 to the first controlled fluid pressure source 8 (not shown in Figure 2). The fluid pressure source 8 is preferably a source of pressurised air. A radial passage 23 leads from the inlet chamber 18 to a stepped axial passage 24 leading to the second housing part 13. A larger diameter part 25 of the passage 24 houses the flow restrictor 4.

The valve passage 17 is a stepped blind bore opening to the inlet chamber 18. An annular valve seat member 26 is screwed into the open end of the passage 17, and has its valve seat 27 at the end adjacent to the closed end of the passage 17. A valve member 28 comprises a poppet valve, having an enlarged head 29 engaging with the diaphragm 19, a stem 30 passing through the valve seat member 26, and a tail portion 31 acted on by a coil compression spring 32 located at the closed end of the passage 17. The valve sealing part 33, which engages with the valve seat 27 to control fluid flow, is an enlarged portion between the stem 30 and the tail portion 31. Differential pressure across the diaphragm 19 acts to deflect the diaphragm 19, which in turn moves the valve member 28 to open or close the valve 7 to vary the fluid flow into the inlet chamber 10. The spring 32 ensures that the valve member 28 follows the movement of the diaphragm 19.

The second housing part 13 has a stepped axial passage 34 contiguous with the passage 25 in the first housing part 12. A larger diameter part of the passage 34 leads to a smaller diameter part 36, leading in turn to a radial passage 37. This leads to an outlet chamber 38. The outlet chamber 38 is sealed by a flexible diaphragm 39, whose periphery is held between an external surface of the housing part 13, and an auxiliary housing part 40. The housing part 40 defines, on the outer side of the diaphragm 39, an outlet control chamber 41, connected through a passage 42 to the second controlled fluid pressure source 10 (not shown in Figure 2). The fluid pressure source 10 is preferably a source of pressurised air, separate from the source 8. A radial valve passage 43 housing the second valve 9 leads from the outlet chamber 38 to an axial passage 44 and thence to an outlet 45 for connection to the device 3 through a line 46.

The valve passage 43 is a stepped blind bore opening to the outlet chamber 38. An annular valve seat member 47 is screwed into the open end of the passage 43, and has its valve seat 48 at the open end. A valve member 49 comprises a poppet valve, having an enlarged head 50 engaging the diaphragm 39, a stem 51 passing through the valve seat member 47, and an enlarged tail portion 52 acted on by a coil compression spring 53 located at the closed end of the valve passage 43.

The valve sealing part 54, which engages with the valve seat 48 to control fluid flow, is on the head 50. As with the first valve 7, differential pressure across the diaphragm 39 acts to deflect it, which in turn moves the valve member 49 to open or close the valve to vary the fluid flow out of the outlet chamber 38. The spring 53 ensures that the valve member 49 follows the movement of the diaphragm 39.

In use, gas from the source 2 flows through the inlet 14, the passage 16 and the valve 7 into the inlet chamber 18, and then through the passages 23, 24 to the flow restrictor 4. It then flows to the outlet chamber 38 through the passage 37, out through the valve 9 and via the axial passage 44 to the outlet 45 and the device 3. The pressures in the inlet and outlet control chambers 21, 41 are chosen to provide the required flow rate by controlling the pressures in the inlet and outlet chambers 18, 38. In normal operation, with steady pressures, the diaphragms 19, 39 are undeflected (as shown) and the valves 7, 9 are partially open, to allow an appropriate fluid flow.

If the inlet pressure increases, the pressure in the inlet chamber 18 rises, and the diaphragm 19 deflects away from the valve 7. The spring 32 ensures that the valve member 28 follows the diaphragm 19, so that the l valve sealing part 33 moves towards the valve seat 27, to reduce fluid flow into the inlet chamber 18. This allows the pressure in the inlet chamber 18 to reduce, so that the diaphragm 19 returns to its normal position.

Conversely, if the inlet pressure decreases, the diaphragm 19 deflects towards the valve 7, moving the valve member 28 so that the valve sealing part 38 moves away from the valve seat 27, to increase fluid flow into the inlet chamber 18, thus increasing the pressure until the diaphragm 19 is in balance again. It will be appreciated therefore that the pressure in the inlet chamber 18 is controlled.

Similarly, if the pressure at the outlet rises, the pressure in the outlet chamber 38 also rises and the diaphragm 39 deflects away from the valve 9. The spring 53 ensures that the valve member 49 follows the diaphragm 39, valve seat 48 to increase the opening of the valve 9, allowing more fluid flow out of the outlet chamber 38 to reduce the pressure in it.

Conversely, if the pressure at the outlet falls, so does the pressure in the outlet chamber 38, and the diaphragm 39 moves towards the valve member 49, causing the valve member 49 to close the valve to restrict the fluid flow out of the outlet chamber 38, in order to increase the pressure in it, until the diaphragm 39 is balanced again.

It will be appreciated therefore that the pressure in the outlet chamber 38 is also controlled. Control of the pressures in the inlet and outlet chambers will therefore control flow through the restrictor 4. If the flow rate through the restrictor 4 needs to be changed, the pressure in the inlet and outlet control chambers can be altered accordingly.

It will be noted that the flow controller of Figure 2 is quite simple in operation, and is designed for ease of manufacture, as the basic housing parts 12, 13 are the same.

It will also be noted that the gas or other fluid whose flow rate is being controlled is separated by the diaphragms 19, 39 from the other pressure sources 8, 10. This is advantageous, as it enables different fluids to be used, while ensuring that there can be no risk of cross- contamination.

In a modification (not shown), the poppet valves 28, 49 may be replaced by spool valves working in appropriate bores in the housing parts, to control the flow of fluid in accordance with the pressures.

Claims

1. A flow controller for fluid flow having an inlet for connection to a source of pressurised fluid, an outlet for connection to a device to be supplied with fluid, and a flow restrictor between the inlet and the outlet, with a first pressure-responsive valve controlling fluid flow between the inlet and the flow restrictor and a second pressureresponsive valve controlling flow between the restrictor and the outlet.

2. A flow controller as claimed in claim 1, in which the flow controller includes an inlet chamber between the first valve and the flow restrictor, and an outlet chamber between the flow restrictor and the second valve.

3. A flow controller as claimed in claim 1 or claim 2, in which each valve comprises a valve member operated by a diaphragm movable in response to differential pressure across it.

4. A flow controller as claimed in claim 3, in which the diaphragm of the first valve is responsive to pressure in the inlet chamber and opposing pressure in an inlet control chamber.

5. A flow controller as claimed in claim 3, in which the diaphragm of the second valve is responsive to pressure in the outlet chamber and opposing pressure in an outlet control chamber.

6. A flow controller as claimed in any preceding claim, in which the control pressure is supplied from a different source from the fluid whose flow is being controlled.

7. A flow controller as claimed in any of claims 3 to 6, in which each valve member is biased towards the diaphragm by a spring.

8. A flow controller as claimed in of claims 3 to 7, in which each valve member comprises a poppet valve.

9. A flow controller as claimed in any of claims 3 to 7, in which each valve member comprises a spool valve.

10. A flow controller as claimed in claim 9, in which the spool valve is spring-biased towards the diaphragm.

11. A flow controller as claimed in claim 1 or claim 2, in which each valve has a valve member comprising a spool valve operating in I dependence on the pressure differential across it, between the inlet or outlet chambers and the respective inlet or outlet control chambers.

12. A flow controller for fluid flow substantially as described herein with reference to and as illustrated in the accompanying drawings.