Instrument Control Valves

http://www.engineeringtoolbox.com/control-valves-t_45.html

If a control valve is part of a closed-loop feedback control system, then calibration is unneccessary. Any errors in the flow can be reduced and eliminated by adding integral action to the controller's characteristics. The practice is known as tuning.

Manufacturers' characteristic information can be relied upon to produce a satisfactorily accurate indication of the performance of any particular valve.

True, if the "loop" is 4-20 madc and you plan to operate in the middle of the range minimal tuning is required. But, it is always wise to verify that the valve calibration is correct i.e. 4 madc is closed and 20 madc open (or vise versa as the case may be), to avoid failure to fully shut or close.

Agreed. The label for this practice varies across the world. Here it is known as 'functional test'.

Vague, your question is.

Each maker will have different ways, they will. An old master I once knew, gave me four screws to turn, he did. Took me half-hour, almost.

Newer one gave me only one screw. Twist it, was all I did. He did the rest. Five minutes, was all he took.

May the force be with you!

The correct word is Cv sizing calculation of Control Valve.

Control valves sizing formula:

Cv = Q x sqrt (SG / DP)

Q is the flowrate in M3/Hr

SG is the Specific Gravity

DP is the Pressure Drop across the control valve.

Basically there are three types of valves (modes of control): The most common is the Equal Percentage, the linear and the Quick Opening or parabolic type.

Control valve may be of : Gate, Globe, Ball, Butterfly or Cam-plug type. Not so common is the V-Notch type for water flow control.

Please follow through these websites, there are ample Engineering information to help you select the right type of control valves.

CV calculation and valve selection

http://www.cheresources.com/valvezz.shtml

A built-in Cv Calculator program in Java at this site for gas, liquid or steam.

tijit

_{digital is our name, portable is our game.}

These websites can be added to 'favourites'.

Thanks.

tell me the formula of cv