control valve size

I am not sure what you are saying is correct.

The control valve selection procedure is a bit complicated, and the valve ports will depend on the Cv value required.

a) Pressure, temparature and their ranges.

b) Liquid, viscosity.

c) Flow.

d) vapour pressure (for cavitation calculations)

e) permissible pressure drop

f) Critical Pressure

etc. From which you calculate Cv and a few other values (like critical pressure ration etc)

Then you select the valve and its ports.

Ajeeshdasv, just for my information, what is your "role" or "title" in the relationship to this question?

A control valve generally performs its function by "pinching down" on the flow through it. This entails some (maybe considerable) pressure drop. This regulation occurs most proportionately if other pressure drops in the line (upstream and downstream) are kept small.

If a full-line-size valve is used, it will often be pinched down to the lowest range of its flow, and the upper range will be almost useless (lots of overshoot or hunting, for instance).

The "Cadillac" arrangement consists of gently tapered "trumpet" reducers before and after the valve, for which there ought to be some good commercial opportunities.

Control valve sizing is based on the calculation of flow coefficient for given pressure drop and fluid flow rate. Main equation that gives relation between flow rate and pressure drop is:

where is:

• C_v - flow coefficient
• Dp - pressure drop through control valve
• Q - fluid flow rate
• G - specific gravity

Flow coefficient is defined as the proportional constant between pressure drop and flow rate and it is determined experimentally by valve manufactures.

Also, velocity or pipe diameter can be calculated using following equations:

This is correct, and, together with prior comments, can be applied to understand the original question.