Valves and valve actuation – Balanced valves – Rotary
Patent
1996-11-27
1998-07-14
Rivell, John
Valves and valve actuation
Balanced valves
Rotary
251309, F16K 3906
Patent
active
057792224
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a tapered plug valve.
The plug of a so-called "pressure balanced" tapered plug valve is conventionally provided with two holes, one connecting the port in the plug to the wide end of the plug and the other connecting the port to the narrow end. This equalises the pressure at both ends of the plug to the line pressure of the line medium flowing through the valve. A non-return valve is often provided in the hole adjacent the narrow end, allowing flow of line medium from the port to the narrow end. Such a valve is disclosed in FR-A-2328905.
However it has been found that in some instances the line medium causes corrosion of the plug and/or deterioration of the lubricant/sealant. Further, if the line medium is dirty or abrasive, the holes can be blocked and/or the non-return valve become damaged, jammed or otherwise caused to malfunction.
U.S. Pat. No. 2,124,359 and U.S. Pat. No. 2,573,238 each disclose a tapered plug valve having a body, a tapered plug in a tapered bore in the body, a shaft which is separate from but drivably connected to the body and a duct in the plug connecting the wide and narrow ends thereof. However sometimes a momentary increase in pressure occurs at the wide end forcing the plug into the bore and causing it to become jammed.
It is an object of the present invention to provide a tapered plug valve which does not suffer from, or suffers less from these disadvantages.
In accordance with the invention a tapered plug valve comprises a body having a passageway therethrough for flow of medium, two chambers and a tapered bore intercepting said passageway, a tapered plug having an outer surface, a wide end and a narrow end rotatably located in the bore and adapted to block said passageway in a closed condition of the valve, one of the chambers being at the wide end of the plug and the other at the narrow end, and a shaft separate from but drivably connected to the plug to cause rotation thereof, the plug having a port adapted to be in communication with said passageway in an open condition of the valve and a channel which does not connect to the port but which connects the wide end to the narrow end to enable equalisation of pressure in the two chambers at the two ends of the plug, characterised in that a non-return valve is positioned in the channel to allow pressure change and associated flow from the wide end towards the narrow end.
The non-return valve thus retains sealant/lubricant in the chamber at the narrow end. This non-return valve is more usually positioned adjacent the narrow end to minimise the volume of sealant/lubricant in the channel and the chamber at the narrow end but may be positioned adjacent the wide end. The pressure change is such that the pressure in the chamber at the wide end reduces and the pressure in the chamber at the narrow end increases until equalisation occurs. However, the pressure at the narrow end may be caused to be greater than that at the wide end thus creating an acceptable imbalance force which assists in preventing the plug from being jammed in the bore.
The channel connecting the wide end to the narrow end may be formed by being directly drilled through the plug, avoiding connection with the port. Alternatively, the channel may be formed by casting a longitudinal groove in the outer surface of the plug and then securing e g by welding, a cylindrical tube in position in the groove. Further alternatively, the channel may comprise a groove formed in the outer surface of the plug and which also carries sealant/lubricant to provide a film between the tapered i e conical, outer surface of the plug and the facing interior surface of the bore.
Five embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which:
FIG. 1 shows a side view, partially in section of a plug of a known tapered plug valve;
FIG. 2 shows a side view, partially in section, of a plug of a tapered plug valve according to a first embodiment of the invention;
FIG. 3 shows a top plan view of the plug s
REFERENCES:
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patent: 2124359 (1938-07-01), Weisgerber
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patent: 2815766 (1957-12-01), Mueller
patent: 3072379 (1963-01-01), Hamer
patent: 3288432 (1966-11-01), Ferrin et al.
patent: 4034776 (1977-07-01), Eshghy
patent: 4174092 (1979-11-01), Macleod
patent: 4614330 (1986-09-01), Kalsi et al.
patent: 5150735 (1992-09-01), Bandy et al.
Hollingworth Keith Jeffrey
Jones Peter Richard
BTR plc
Rivell John
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