This invention relates to a valve means for controlling fluid flow from a supply to a pressurised vessel, such as a pressurised sealing means.

It is known for tanks which store fluid (usually liquid) to have pumps to remove the fluid from the tank. The pump outlet may have a pressurised rotary seal to prevent leakage out of the tank at the seal because of a pressure differential. However, there can be a problem if the fluid in the pressurised seal leaks, as the fluid will tend to enter the tank, and potentially contaminate the contents. If the seal leaks, it will need topping up from a fluid supply, and if it leaks too much, fluid will be wasted. It is known for fluid to be supplied to the seal through a valve which closes if too much fluid is flowing. This arrangement does not allow for the possibility that the leak stops, which can happen if it is due to an imbalance which is righted. In this event, the seal will fail to operate properly, and will allow leakage from the tank.

According to the present invention, a valve means for controlling fluid flow from a supply to a pressurised seal chamber comprises a metering valve and a non-return valve, such that fluid flows from the supply to the seal chamber through the metering valve and the non-return valve, with the metering valve being operative in response to the pressure of the supply and the pressure in the seal chamber, and closing to prevent fluid flow to the seal chamber when the pressure differential between the supply and the seal chamber exceeds a predetermined level, the metering valve also having a bypass allowing a constant restricted fluid flow from the supply to the seal chamber through the non-return valve.

Thus, the metering valve is normally open to allow fluid flow to the seal chamber, as long as the pressure in the seal chamber is within the allowed pressure differential (that is, the supply pressure is not greater than the seal chamber pressure by more than a given amount) . Any small leaks from the seal chamber are topped up by fluid flow through the bypass and the metering valve. If a substantial leak occurs, the seal chamber pressure drops and the pressure differential exceeds the predetermined level. The metering valve then closes, so that the seal chamber is supplied only by the restricted flow through the bypass. This limits the amount of fluid that is wasted. If the leak stops, the pressure in the seal chamber will gradually rise, and so the metering valve will re-open once the pressure differential falls below the predetermined level. The valve therefore allows normal operation to be resumed if the leak stops, and less waste of fluid overall.

Preferably the metering valve comprises a spool valve having a spring- loaded spool working in a bore in a housing. Fluid flows from the supply round the spool and to the non-return valve.

The metering valve may include means indicating when it is closed. The indicating means conveniently comprises a button carried by the spool, the button projecting out of the housing when the valve is closed. This provides a visual indication that the valve has closed, and hence that there is a problem with the seal pressure.

The metering valve may also have an open, non-metering position, used for initial pressurisation of the seal chamber. This allows an unrestricted flow from the supply to the seal chamber, to provide rapid pressurisation initially. The metering valve is preferably operated manually to achieve the open, non-metering position. Where the valve is a spool valve, it may be moved into the open, non-metering position by manual operation of the indicating button into the housing. The bypass preferably comprises a restricted passage in the housing leading from the supply to the non-return valve. The bypass may include an adjuster valve to vary the amount of fluid flow through it. The adjuster valve may comprise a needle valve accommodated in the housing, and adjustable from outside the housing.

The fluid flow valve may also include a pressure regulator to ensure constant pressure of the fluid supplied to the seal chamber. The regulator is accommodated in the housing between a supply port and the metering valve.

An embodiment of the invention is illustrated, by way of example, in the accompanying drawings, of which the single Figure is a longitudinal section through a fluid flow control valve means.

The fluid flow control valve means 1 shown in the Figure is operative to control fluid flow from a supply 2, typically of water, to a pressurised seal chamber 3 for a rotary seal for a shaft 4 of a pump 5 operating to pump the contents out of a storage tank 6 as required.

The valve means 1 comprises a main housing 7 accommodating a metering valve 8, a non-return valve 9 and a bypass 10 for controlling fluid flow from an inlet 11 connected to the supply 2 to an outlet 12 connected to the seal chamber 3. A pressure regulator 13 of known form is provided between the inlet 11 and the metering valve 8.

The housing 7 has a primary stepped longitudinal bore 14 into which the inlet 11 opens. At the inlet end the bore 14 has a portion 15 of greatest diameter, and it steps down towards the outlet end, where it has a larger diameter counterbore 16. At the inlet end the bore 14 is closed by a plug 17 received sealingly in the bore portion 15. The plug 17 has an outwardly-opening blind bore 18 which forms a supply chamber 19 and houses the pressure regulator 13. As this is of known construction, it will not be described further. The pressure is adjusted by means of a cup member 20 in turn closed by a cap 21. The plug 17 has an inwardly -facing blind bore 22 surrounded by an annular blind bore 23.

The inlet 11 opens into a land 24 on the plug 17, connected to the supply chamber 19 by a radial port 25. An axial passage 26 connects the supply chamber 19 via the radial port 25 to the annular bore 23, which opens into a metering valve inlet chamber 27 in the primary bore 14, and in which the metering valve 8 works.

The metering valve 8 comprises a spring-loaded stepped spool 28. It has a central portion 29 of larger diameter sliding in a bore portion 30 and two end portions 31,32 of smaller diameter. The inlet end portion 31 slides in the blind bore 22 through a seal 33, while the outlet end portion 32 slides in a small diameter portion 34 of the primary bore 14 through a seal 35, and projects into the counterbore 16. The outlet end portion 32 carries an indicating button 36, normally housed in the counterbore 16.

A metering valve seal 37 is on a central portion of the spool 28, and cooperates with an inclined seat 38 in the bore 14 to meter fluid flow from the metering valve inlet chamber 27 to a metering valve outlet chamber 39 formed in the bore 14 between the valve seat 38 and the seal 35. The valve 8 can close completely to shut off flow between the chambers 27 and 39. The spool 28 is biased to a normal position by an inlet spring 40 acting between the end of the annular blind bore 23 and a shoulder between the central spool portion 29 and the inlet end portion 31, and an outlet spring 41 accommodated in the chamber 39, to act between the housing 7 and the spool 28. The outlet chamber 39 has a radial passage 42 leading to the non-return valve 9, which is housed in the outlet 12. The non-return valve 9 comprises a simple ball valve, with a ball valve member 43 co-operating with an inclined seat 44 surrounding the passage 42, and biased towards the seat 44 by a spring 45 abutting a plug 46 fixed in the outlet.

The bypass 10 comprises a radial passage 47 leading from the metering valve inlet chamber 27 to an axial passage 48 which in turn is connected to the radial passage 42 by a cross passage 50. The bypass therefore provides a constant fluid flow from the inlet chamber 27 to the non-return valve 9. A valve 49 is provided in the passage 48 to enable the flow rate to be adjusted. The valve 49 is a needle valve (not shown in detail) accommodated in the axial passage 48, which is open at the outlet end of the housing 7, to allow for adjustment. It will be appreciated that the adjuster valve 49 is only able to adjust flow through the passage 48, and is not able to affect flow from the outlet chamber 39 to the non-return valve 9, as the passages 48 and 42 are in fact spaced from each other, but connected by the passage 50.

Thus, in use, fluid from the supply 2 is supplied at a regulated pressure, due to the pressure regulator 13, to the supply chamber 19, and from there to the metering valve inlet chamber 27 through the passage 26 and the annular bore 23. Flow round the central portion 29 will be relatively restricted. It then passes through the open metering valve 8 to the outlet chamber 39, and through the passage 42 to the non-return valve 9. At the same time, fluid flows through the bypass 10 from the chamber 27 to the non-return valve 9.

If there is a leak in the chamber 3, this will cause a pressure differential across the non-return valve 9, so that the valve 9 will open to top up the chamber 3. The pressure in the metering valve outlet chamber 39 will fall, causing the metering valve 8 to move towards its closed position, thus restricting flow.

As long as the leak is relatively small, the pressure differential between the chamber 3 and the metering valve outlet chamber 39 will not be very great. However, if there is a substantial leak, the pressure differential will be greater, and once it exceeds a pre-determined level (set by the values of the springs 40 and 41) the metering valve 8 closes to prevent further flow from the outlet chamber 39. Closure of the metering valve 8 will cause the indicating button 36 to project out of the housing 7, to provide a visual indication of a substantial leak. The seal chamber 3 will still be supplied via the bypass, although at a relatively small flow rate.

If the leak is corrected, the fluid supplied via the bypass will fill up the chamber 3 (although quite slowly), so that it will be re-pressurised. When the pressure differential falls below the predetermined level the metering valve 8 will open again, allowing normal operation to be resumed. This will be indicated by the button 36 returning to its position within the counterbore 16.

When the valve means 1 is first installed, it will naturally be necessary to pressurise the seal chamber 3. In order to achieve this rapidly, the indicator button 36 is manually pushed into the housing 7. This causes the spool 28 to move towards the inlet end, ensuring that the metering valve 8 remains open, and moving the central spool portion 29 into a larger diameter bore portion, to allow greater fluid flow past the metering valve 8. Once the seal chamber 3 is pressurised, the non-return valve 9 closes, and the spring 40 returns the spool 28 to the normal operating position shown. Thus, the valve means 1 provides for rapid initial pressurisation of the seal chamber 3, compensation for normal leakage, and closure of the metering valve 8 for substantial leakage, as well as the possibility of recovery from a substantial leak. This is achieved with a minimum of wasted fluid.