Valves and valve actuation – Rotary valves – Butterfly
Patent
1998-01-26
2000-02-08
Fox, John
Valves and valve actuation
Rotary valves
Butterfly
251214, F16K 122
Patent
active
060220007
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a valve device, particularly a valve for corrosive and/or delicate liquids, such as liquid chemicals and liquid foods. The valve device comprises a body, a shutter operated by a shaft guided in a neck of the body and a sealing sleeve fitted with a collar which extends over a certain length along the neck.
When a valve of this kind is installed on pipework carrying a pressurised fluid, it must not constitute a weak point and it must ensure the continuity of the enclosure formed by the pipe in relation to the pressurised fluid. No leaks to the outside are permissible, either at the connection to the upstream and downstream pipes or at the passages for the shafts which operate and guide the shutter.
The sleeve enveloping the body provides all the seals needed for the valve: the upstream-downstream seal, the seal at the junctions with the pipework and the seal around the shaft passages. To ensure the upstream-downstream seal at the shutter, but also at the bearing surface for the shaft passage, the sleeve may comprise resilient means which serve to create the necessary pressure. In the case of an elastomeric sealing sleeve, the resilient means consist of the sleeve and collar themselves. In the case of a sleeve made of plastomer, a flexible cushion placed between the body and the sleeve constitutes the resilient means.
To reinforce the seal of the enclosure, a second seal may be provided, operating as a stuffing-box around the shaft.
STATE OF THE ART
In the case of elastomer sleeves the sealing of the shaft passages is achieved by compression of the collar of the sleeve surrounding the shaft between the body, the shaft and the shutter. Apart from the fact that this is a dynamic seal, the parameters which determine the compression of the elastomer for a given level of seal are subject to variations depending on the operating conditions of the tap, particularly pressure variations.
In patent application DE-A-24 60 182, there is a description of a butterfly valve in which the butterfly rotates about a shaft passing through an annular seating, the U-shaped section of which surmounts the inside and flanks of the valve body. This butterfly valve comprises, on the one hand, a first seal on the bearing surface of the shaft passage, provided by a compressed flexible cushion, and on the other hand, around the part of the shaft which passes through, a sealing washer held tight by resilient means, e.g. a compression spring, between the bearing of the shaft and the seating. This second seal is a back-up seal in case the first seal fails.
The publication DE-C-20 27 775 discloses a butterfly valve wherein the sealing sleeve is fitted with a collar extending along the shaft. This collar is sealed by means of a stuffing-box placed between the collar and the neck of the tap body, this assembly forming the second seal, whilst the first seal is provided at the bearing surface for the shaft passage.
The publication EP-A-0 411 652 discloses a valve with a spherical bushing fitted with a second sealing system made up of an elastomeric torus accommodated in a ring in a plain bearing guided in the body. These types of construction have the drawback that the seal of the shaft depends on deformations of the shaft or variations in temperature. In the closed position, the shutter is subjected to the differential pressure between upstream and downstream. This differential pressure creates a radial force on the shaft and the shaft has a tendency to move radially downstream. The movement results, on the one hand, from the take-up of the guidance play of the shaft in the bearing of the body and the fitting play between the shaft and the shutter, and, on the other hand, from the deformation of the shaft and the shutter under the effect of the load caused by the pressure on one side of the shutter.
Deformation of the parts under the effect of the loads is inevitable. The play between the shaft and the collar increases on the upstream side and the components of the first seal are unloaded on the upstr
REFERENCES:
patent: 4759530 (1988-07-01), Iff
Gebrauchmuster DE, U, 90 04610 Pfannenschmidt Sep. 20, 1990.
Dubois Jean-Paul
Garrigues Jean-Claude
Guiroy Patrick
Laulhe Rene
Wattignier Claude
Fox John
KSB Aktiengesellschaft
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