Technical Field This disclosure relates to a flexible sealing arrangement for use in valves and pumps which include a reciprocating shaft.

Background Valves and pumps which utilise a reciprocating shaft will often include a shaft sealing arrangement, such as a gland seal, which seals between the housing of the valve or pump and the reciprocating shaft. One example of this is found in dart valves which are typically used on float cells in mining slurry applications. Dart valves control the balance and levels of slurry through the float circuits at mine sites. The valve includes a shaft which is actuated linearly by various means but typically by a pneumatic actuator. The shaft is usually also fitted with positioners.

The shaft of the valve is sealed with the housing of the valve by way of a gland seal which typically utilises either braided packing or moulded rubber Vee or chevron type packing. The valve also includes a guide bush which is used to guide the shaft through the packing.

There is an ongoing need to repair the gland seal on dart valves used on float cells. The ongoing need to repair the valves gland area causes considerable downtime and cost to the mine sites as the whole float circuit needs to be bought down to maintain the valves.

Another problem associated with these valves is the loss of control of the valve due to slurry build up on the shaft which can result in the shaft jamming in the guide bush. This limits the amount of available movement of the shaft to such a degree that the valve is gradually forced into the fully open or fully closed position. It would be desirable to address at least one of the problems outlines above.

Summary In a first aspect there is provided a valve or pump including: a reciprocating shaft; a housing; the reciprocating shaft extends through the housing; the housing includes a shaft sealing arrangement which seals the shaft with respect to the housing; and a flexible seal is provided inside the housing, the flexible seal prevents the fluid being controlled by the valve or pumped by the pump from coming into contact with the shaft sealing arrangement; and a fluid inlet to permit the region enclosed between the flexible seal and the shaft sealing arrangement to be occupied by pressurised fluid.

The shaft sealing arrangement may include a gland seal.

The housing may further include a shaft mounting arrangement and the flexible seal may further prevent working fluid from coming into contact with the shaft mounting arrangement.

The shaft mounting arrangement may include a guide bush.

The shaft surrounding portion may include a valve seat region which is arranged to seal with the housing in use to permit replacement of the shaft sealing arrangement.

The valve or pump may further include a shroud member which surrounds the flexible sealing arrangement.

The shroud member may include a metal body with a protective rubber coating.

The flexible seal may be secured by the shroud member.

In a second aspect there is provided a seal including: a shaft surrounding portion which includes an aperture which is arranged to surround a shaft; a peripheral portion which is arranged to be clamped between parts of a housing of a valve or pump; and a flexible portion extends between the shaft surrounding portion and the peripheral portion.

The shaft surrounding portion may include a valve seat region which is arranged to seal with a housing in use to permit replacement of a shaft sealing arrangement.

The flexible portion may be formed from a more flexible material than those used to form the peripheral portion and the shaft surrounding portion.

In a third aspect there is provided a method of retro-fitting a flexible seal to a pump or valve including the steps of fitting a flexible seal according to the second aspect.

Brief Description of the Drawings

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a cut away view of a prior art dart valve;

Figure 2 is a partial cross-sectional view of an embodiment of a dart valve; Figure 3 is a cross sectional view of another embodiment of a dart valve; Figure 4 is a partial cross-sectional view in the region of the flexible seal of the dart valve of figure 3; and

Figure 5 is a cut away view of the flexible seal of the dart valve of figure 3.

Detailed Description

Referring to figure 1, an example of a prior art dart valve 10 is shown for use in controlling flow of slurry in flotation mineral processing. Dart valve 10 includes a housing 12 including a guide bush 13 in which is mounted a shaft 14 which carries a valve element 16. Pneumatic actuator 20 is attached to shaft 14 and is controllable to move shaft upwards and downwards as shown in the figure to move valve element 16 in relation to valve seat 18 to control the flow of slurry through the valve from inlet 30 to outlet 40. A gland seal 22 seals between the shaft 14 and the housing 12 to prevent the escape of slurry from the valve.

Referring to figure 2, a partial view of a dart valve 100 is shown being a modified version of dart valve 10. Like reference numerals in the series 100 will be used to denote like components.

The dart valve 100 principally differs from dart valve 10 by the addition of a flexible seal in the form of diaphragm seal 150. Diaphragm seal includes a shaft surrounding portion in the form of ring 154 which surrounds the shaft 1 14 and clamps to the shaft near to the valve member 1 16 to allow the full shaft travel. The diaphragm seal 150 also includes a peripheral portion in the form of clamping portion 152 which is clamped between the top plate flange 1 12a of housing 1 12 and the main body 1 12b of the housing. An intermediate flexible diaphragm portion 156 extends between ring 154 and clamping portion 152.

An actuator (not shown) is arranged to move shaft 1 14 in an upwards and downwards direction as shown in figure 2 to move valve element 1 16 to cooperate with a valve seat (not shown) to control the flow of fluid through the valve in an identical manner to the valve 10 of figure 1.

The diaphragm seal 150 creates a barrier which maintains fluid in the valve (slurry) below the diaphragm seal 150 as seen in figure 2. The diaphragm seal therefore prevents slurry from coming into contact with both the gland seal 122 and guide bush 1 13 areas of the valve.

The region 160 between the diaphragm seal 150 and top plate 1 12a and gland area can be pressure balanced by filling with water or other appropriate fluid via a fluid inlet 170 provided in the top plate 122a so that the region is pressure balanced to the slurry pressure on the other side of the diaphragm seal 150. The fluid used to pressurise the region 150 is substantially free from debris and does not cause damage to the gland seal or fouling of the guide bush.

Ring 154 includes a valve back seat region in the form of valve seat 155 which seals against the guide bush 1 13 when the shaft 1 14 reaches its uppermost limit of travel. The sealing of the valve seat 155 against guide bush 1 13 enables replacement of the packing 122a in the gland seal 122 even whilst pressurised fluid is present inside valve 100.

Diaphragm seal 150 may be manufactured via a moulding method utilising a dual compound. A material such as Linard™ HDS (70 duro) produced by Weir Minerals (www.weirminerals.com) is used to form the clamping region 152 which is designed to act as both a gasket and seal. The diaphragm portion 156 centre section is formed from a more flexible material such as Linatex material produced by Weir Minerals (www.weirminerals.com) and can be either flat or corrugated to allow for the maximum amount of lineal movement in line with the shaft movement. The ring 154 is formed from Linard™ HDS (70 duro) to allow a firm clamping force onto the shaft 114.

Referring to figure 3, another embodiment of a dart valve 200 is shown. This valve differs from that shown in figure 2 in that a flexible sealing member in the form of cone seal 250 is used instead of the diaphragm seal. The cone seal 250 is surrounded by a shroud member in the form of shroud 280.

Referring to figure 4, the region of the cone seal is partially shown in enlarged detail. The cone seal 250 is shown in solid lines in a position where the shaft 214 of the dart valve 200 is in a partially lowered position in which the dart valve is partially open. The cone seal 250 is shown in dotted lines B in the position it adopts when shaft 214 is in the fully lowered position and the dart valve 200 is fully open.

Cone seal 250 includes a shaft surrounding portion in the form of ring 254 which surrounds the shaft 214. The cone seal 250 also includes a peripheral portion in the form of clamping portion 252 which is clamped between the top plate 212 and the shroud 280. An intermediate flexible portion 256 extends between ring 254 and clamping portion 252.

Shroud 280 is formed from a generally tubular metal body that is coated with rubber on its outside surface. Shroud 280 protects the flexible seal from direct impingement of the incoming slurry so that it is not deformed.

As for the previously described embodiment, the region between the cone seal 250, top plate 212 and gland area can be pressure balanced by filling with water or other appropriate fluid via a fluid inlet (not shown) provided in the top plate 212 so that the region is pressure balanced to the slurry pressure on the other side of the cone seal 250. The pressure balance pressure can be directly proportional to the underside pressure through the use of a pressure transmitter and proportional control valve or via a hose taken to the same head height as the pressure through the valve. This balanced pressure relieves stress on the flexible seal. In low pressure applications pressure balancing is not required.

Referring to figure 5, seal 280 is shown in isolation before assembly into a valve or pump. It can be seen that seal 280 is moulded in a general cone shape. The ring 254 is pushed up inside the flexible portion 256 at the time of assembly.

Although the foregoing description was based on a dart valve this disclosure is relevant to other types of valves. This disclosure is also applicable to pumps which utilise a reciprocating shaft.

It can be seen that embodiments offer at least one of the following advantages:

• fluid which is being controlled by a valve or pumped by a pump is prevented from coming into contact with the gland seal which prevents adverse impact on the gland material and subsequent wear and leak path.

• fluid which is being controlled by a valve or pumped by a pump is prevented from building up on the shaft to such an extent that the shaft can no longer freely move through the guide bush and gland packing.

• Dual compound diaphragm seal allows flexibility and high bolt loads on the gasket areas

• No modification of the valve or pump structure is needed as the diaphragm seal is designed to be retrofitted to existing designs and to be incorporated in newly manufactured valves and pumps

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.