Fluid handling – Processes – Cleaning – repairing – or assembling
Patent
1992-02-19
1994-01-18
Chambers, A. Michael
Fluid handling
Processes
Cleaning, repairing, or assembling
137375, 251267, 251368, F16L 5518
Patent
active
052793206
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a gate valve comprising a valve body and a gate displaceably arranged inside said valve body transverse to the flow direction, said gate being provided on each side with a guide groove guided by means of a mating guide rail formed on each side of the valve body, whereby the gate comprises a gate core provided with a coating thereon comprising a softer moulded polymeric material, preferably an elastomer, which in the sealing surface areas of the gate sealingly abuts the corresponding seat surfaces of the valve body in the closed position of the gate and a harder and more wear-resisting polymeric material provided at least in the guide grooves.
BACKGROUND ART
Gate valves of the above type are known which comprise a gate coated on the outside with rubber except for the guide areas. The gate is often made of cast iron with the result that corrosion problems may arise. As a consequence thereof gates entirely coated with rubber are commonly used today. However, a disadvantage of coating the guide areas with soft rubber is an increased friction and wearing off of said guide areas in some situations, such as when the valve is used for extremely high pressures. The increased friction causes in turn an increase in the stem force for opening and closing the valve.
U.S. Pat. No. 4,532,957 discloses furthermore a gate valve with a gate comprising a gate core. On each side the gate core comprises a groove wherein a plastic insert of a harder material is placed. The plastic insert forms a guide groove for mating guide rails inside the valve body. The entire outer surface of the valve gate except for the guide grooves is coated with a softer rubber material.
The manufacture of such a gate involves the steps of first manufacturing the inserts in a separate mould followed by placing the inserts in the grooves inside the gate core, said gate core subsequently being coated with rubber in a second mould.
European printed accepted specification No. 01 46 112 discloses furthermore a valve gate coated on the entire outer surface with a softer rubber-elastic material and provided with a U-shaped harder plastic insert on each side. The plastic insert forms a guide groove for guide rails in the body and is embedded in the rubber-elastic material, i.e. it is encapsulated by said material except for in the guide groove. Also the manufacture of such a gate involves the steps of manufacturing the inserts in a separate mould followed by a placing thereof together with the gate core in a second mould so as to provide the rubber coating.
DISCLOSURE OF INVENTION
The object of the invention is to provide a gate valve of the above type and comprising a corrosion-protected gate which possesses excellent sliding properties in the guide areas, and the manufacture of which is simple and inexpensive.
The gate valve according to the invention is characterised in that the harder material is moulded at least in the guide grooves, in that the softer and the harder polymeric materials are molecularly compatible and molecularly interconnected in their transition areas. As a result, the gate can be manufactured in a simple and inexpensive manner by means of only one mould while achieving an excellent protection against corrosion and good sliding properties in the guide areas. A further advantage is simultaneously achieved because the risk has been elimimated of the two coating materials being separated in service of the valve. Such a separation of the two coating materials might otherwise cause a malfunctioning of the valve and a corrosion of the gate core.
According to the invention a portion with the harder material may be provided in the sealing surface areas of the gate, preferably adjacent the bottom of said gate, and the surface of the harder material may be recessed, preferably by 2 to 4 mm, relative to the surface of the surrounding softer material. As a result, the gate is stopped almost instantaneously when the valve is being closed, and in addition said stop is perceptible when the valve is being
REFERENCES:
patent: 4532957 (1985-08-01), Battle et al.
AVK Maskinfabrik A/S
Chambers A. Michael
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