Measurement of Control Valve flow coefficient (Cv)

Measurement of control valve flow coefficient(Cv) is very important for knowing the performance of the control valve. The manufacturer determine the control valve flow coefficient(Cv) after manufacturing the control valve, and engraves Cv data in the nameplate. We can find the control valve flow coefficient data on the nameplate of the valve. In this topic, we will discuss the importance of measurement of flow coefficient of control valve.

Before writing the Cv data in the nameplate, the manufacturer test the valve for flow coefficient. Water of specific gravity 1.0 at 60 60 degrees Fahrenheit is suitable for the Cv determining test. After testing the valve for its Cv, the data is mentioned on the nameplate.

flow control coefficient Cv

Why to Measure Control Valve flow coefficient (Cv)?

The followings are the reasons for measurement of Cv.

  1. It is easy to compare the different valves flow capacity by measuring control valve flow coefficient.
  2. It assist in selection of the right size control valve for a particular application.
  3. We can easily understand the valve characteristics by calculating Cv. Therefore, It is easy to determine the effect of valve on the pressure in the system.

Practical Use of flow Coefficient(Cv)

The flow coefficient is very important for sizing of the valve. The size of the valve decides the flow that can pass through its opening. If the opening is too small, it would cause pressure drop that can cause liquid drop below its vapor pressure. This further leads to implosions that cause wear in the valve trims. This phenomenon is called Cavitation.

In this condition, the flow coefficient deviates from the flow calculated using the flow coefficient equation for sizing control valves. The reason behind this is the vapor bubbles occupy more volume because the mass of liquid expands during the phase change. and it creates an extra resistance to flow.  

All these reasons assist for measurement of Control Valve flow coefficient (Cv).

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