Control Valves and Line Size

What does the Process Description document say on the topic?

Hi there,

You need to look at this as an overall picture.

1. What is the required flow rate (Cv)

2. What is the process data

3. What is the line size, and the valve size to be.

You then need to do a few calculations.

It would be very expensive indeed to make all your control valves the same size as the line size. You would like to know whether you have chocked flow, turbulant flow etc.

I would advise you to get hold of the ANSI/ISA-75.01.01-2002 standard (Flow equations for sizing control valves). You should also dowload the fisher control valve hand book. www.emmersonprocess.com

This will explain to you the effect and the maths behind reducers and things that go with the control valve.

Regards,

Craig

Control valves that perform a regulating function ( not full open or full closed) need to be sized. They act as a "pressure bank" in the system and therefore have to be carefully sized to obtain the desired control. Hence the Cv of the valve must be calculated. If this is done properly, you will find that tuning in the valve to operate automatically will be easy and your desired setpoint will be maintained well. Generally you will find that the size of the valve will be smaller than the line size ( not always!). Hopefully you have your line size properly calculated as well.

Genrally the valve port size will be smaller than the pipe line, it is so, because to reduce cost. this type of valve is called as reduce port size valve and the valve which have port size equal to line is called as full port valve. valve port size should not be less than 50% of the line dia. CV value plays an important role in determining the size of the port in control valves.