Terms Questions
- What is the capacity coefficient (Cv value) of a valve?
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The capacity coefficient of a valve indicates a “coefficient that represents the capacity of flow at a given travel under certain conditions.” (From JIS B 0100, Glossary of Terms for Valves)
It is a coefficient that expresses something like the performance that allows fluid to flow through a valve under specified conditions such as the valve opening degree and the pressure difference before and after the valve (differential pressure). The Cv value is often used as one of the capacity coefficients. The larger the Cv value, the easier the fluid to flow.
- What is chattering?
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Chattering is a phenomenon in which the valve disc of a check valve hits the seat surface of the valve casing or the valve disc or arm hits the valve casing.
Unstable fluid flow such as fluctuations in flow velocity, turbulence and pulsation may cause chattering due to unstable opening of the valve disc.
- What is water hammer?
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Water hammer is a phenomenon in which the momentum of water in a water pipe changes in a short period of time and an abnormally large pressure wave is generated in the pipe. The cause is ① sudden opening / closing of the valve or ② sudden start / stop of the pump. When water hammer occurs, not only the valve may be damaged, but also the devices, etc. connected to the piping may be damaged. Therefore, it is necessary to pay attention to water hammer. As a countermeasure, close the valve as slowly as possible. Alternatively, we recommend that you consider a wafer type check valve or counterweight type check valve.
- Tell me the difference between gauge pressure and absolute pressure.
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Gauge pressure is the pressure using the atmospheric pressure as the reference (0).
The unit display is G”, but it is often omitted.
The conversion formula from absolute pressure is [Gauge pressure = Absolute pressure – Atmospheric pressure].Absolute pressure is the pressure using an absolute vacuum pressure as the reference (0).
The unit display is A” or ”Abs”, but it is often omitted.
The conversion formula from gauge pressure is [Absolute pressure = Gauge pressure+ Atmospheric pressure].