Valves and valve actuation – Mechanical movement actuator – Gear
Patent
1996-10-21
1998-02-03
Fox, John
Valves and valve actuation
Mechanical movement actuator
Gear
251228, F16K 116
Patent
active
057135568
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a valve to be installed in a fluid transport line to regulate stop fluid flow by composite actions of a valve element relative to a valve seat. In this description, the term "fluid" is used as a general term for liquids and gases.
BACKGROUND ART
As is generally known, butterfly valves, gate valves, ball valves and globe valves have universally been used for regulating and stopping fluid flow.
In most prior art valves, a valve element fixed to an arm member is opened and shut by operating a handle or the like. Such valves are economical in their own as long as the valves are used under non-severe service conditions. However, various technical problems arises in prior art valves due to structural restrictions thereon the valves are used under severe service conditions for handling high-temperature, high-pressure slurry, corrosive fluids or the like.
Examples of technical problems that may arise in prior art valves will be explained.
(A) As regards the butterfly valve shown in FIG. 2, head loss across butterfly valves due to resistance exerted by butterfly valves on fluid flow is low when the butterfly valve is in a fully open state. The structure of butterfly valves requires the valve element to sidle up to the valve seat to rest on the valve seat. (Such a mode of closing movement of the valve element will be referred to as "slide sidling" for the sake of convenience in the following description.) Slide sidling of the valve element entails the abrasion of sealing surfaces that deteriorates the tightness of the sealing surfaces. It is difficult to achieve uniform, close contact between the sealing surfaces even if the sealing surfaces are formed in spherical surfaces or an eccentric valve element driving shaft is employed. Furthermore, the valve element and the valve seat will be damaged if a foreign matter is stuck between the sealing surfaces when seating the valve element on the valve seat. Although various attempts, such as putting elastic members on the sealing surfaces, have been made to secure satisfactory tightness, those attempts are symptomatic means merely capable of supplementing imperfect tightness. Durability of elastic members formed of rubber or the like is insufficient when used under severe service conditions, such as conditions requiring handling high-temperature, high-pressure slurry, corrosive fluids or the like. Elastic members of a metal must be formed in a very intricate construction to provide the elastic members with satisfactory elasticity.
(B) As regards gate valves, the valve element slides substantially in parallel to the valve seat for opening and shutting. Therefore, gate valves exert high resistance on fluid flow, cause rapid abrasion, and need elastic members to be put on the sealing surfaces to secure satisfactory tightness, which entails problems similar to those entailed by butterfly valves.
(C) As regards ball valves, head loss across ball valve due to resistance exerted on fluid flow is low when the ball valve is in a fully open state. However, the mating surfaces of the valve element and the valve seat must be finished in precision spherical surfaces, elastic members need to be put on the sealing surfaces to secure satisfactory tightness, which entails problems similar to those entailed by butterfly valves.
(D) Globe valves are less subject to problems in material and machining than butterfly valves, gate valves and ball valves, and are capable of securing satisfactory tightness. However, head loss across globe valves due to resistance exerted on fluid flow is large when the globe valves are in a fully open state.
The problems discussed in (A) to (D) by way of example become more serious as the size of valves increases and result from the interrelation of intricate conditions. Accordingly, it has been believed that it is difficult, from the viewpoint of structure, to simultaneously achieve reduction of head loss when the valve is fully open, avoidance of frictional abrasion due to the slide sidling and the uniform, cl
REFERENCES:
patent: 2809010 (1957-10-01), Lpsey et al.
patent: 5078363 (1992-01-01), Gregory
Fox John
Kabushiki Kaisha Yokota Seisakusho
Yokota Hiroshi
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