In daily life, we often see a variety of butterfly valves. The shape and function are different of each kind of butterfly valve. Next, this article will introduce the difference between these butterfly valves.
1. Concentric Butterfly Valves:
The butterfly valve is characterized in that the valve stem axis, the butterfly plate and the body are at the same position. The structure is simple and convenient to manufacture. A common rubber valve belongs to this category. The disadvantage is that the butterfly plate and the valve seat are always in a state of being squeezed and scraped, resulting in a large resistance distance and a rapid wear. In order to overcome the extrusion, scratching and ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or PTFE, but it is also limited in temperature by use, which is the reason why people traditionally considered that the butterfly valve is not resistant to high temperatures.
2. Single Eccentric Butterfly Valve:
In order to solve the extrusion problem of the butterfly plate and seat of concentric butterfly valve, a single eccentric butterfly valve is produced. Its structure characteristic is that the axial center of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotary shaft center, which reduces the over extrusion between the upper and lower ends of the butterfly plate and the seat. However, the scraping phenomenon between butterfly plate and valve seat has not disappeared in the whole process of valve switch with single eccentricity, which is similar to concentric butterfly valve in application scope, so it is not used much.
3. Double Offset Butterfly Valves
The double offset butterfly valves formed from the further improved single eccentric butterfly valve are now widely used. Its structural feature is that the stem axis is both deviated from the disc and away from the body. The double eccentric effect makes the butterfly plate quickly disengage from the valve seat after the valve is opened, which greatly solves the unnecessary over-squeezing and scraping of the butterfly plate and the valve seat, reducing the opening resistance distance and wear, and providing long service life of valve seat. The scraping is greatly reduced, so that the double offset butterfly valve can also adopt a metal valve seat, which improves the application of the butterfly valve in the high temperature field.
4. Triple Offset Butterfly Valves
The triple offset butterfly valve is eccentric at the axial position of the double eccentric stem, and the center line of the conical sealing surface is deflected by an angle with respect to the center line of the valve to form a third eccentricity. The third eccentricity allows the valve seat and the disc to be completely disengaged throughout the entire stroke of the valve. The contact between the disc and the valve seat is only a moment in sealing, thus greatly reducing the friction of switching process between the valve seat and the disc. Since the sealing is achieved by the compression between the valve seat and the sealing ring on the butterfly plate, the sealing specific pressure can be applied by the torque of the valve stem. If the valve structure is designed properly, an extremely high sealing effect can be achieved. The design of triple offset butterfly valve can solve the problem of high temperature resistance and leakage prevention. As a high performance valve, the triple offset butterfly valve has become the first choice in the regulating valve market with its unique structural characteristics and performance advantages.
Next: Causes and Solutions of Ball Valve Internal Leakage
Previous: Valves for water supply pipeline and their installation positions