Control valve bigger than line size


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What happens if I use a control valve one size higher than the line size? I know we always use a line size control valve or one size less than the pipe line. Since I have a situation where vendor can not give 1/2" valve but offered 1" valve, where as the line size is 1/2". Checked line sizing and 1/2" line is perfectly O.K.

Can anybody clarify? Thanks in advance.

Steve Myres, PE

I think you may run into difficulties with this setup. The larger the valve is, the lower the velocity through the limiting oriface at given flow. I think you may find that there is very little change in flow over a wide change in valve
percentage position, say going from 100% to 20%, then abrupt change from 20% to 0%. This can lead to unstable operation if in a closed loop, as well as inaccurate control.

James Fountas

I assume you are refering to a control valve (variable position 1-100% open) and not a solenoid vale (open/closed only).

You can generally use a control valve that is larger or smaller then the line size. You have to make sure the Cv rating is correct for the application. The proper characteristics (equal percentage, linear, or quick open) are just as important as Cv for an application.

James Fountas
[email protected]
If accurate control is critical then go through the sizing calcs.

If you just need a half baked on-off valve then go for it.

Bob Pawley
Normally, the only problem on valve size bigger than the line size is the cost. But in this case, the cost of 1/2" valve (small size valves) is almost the same with 1" valve. Technically, I believe that it should be okay. So, do not worry about it.

Abdul Rifai
If the purpose of the valve is to attenuate flow, it can do this only by presenting a significant resistance and resultant pressure drop. A too-large valve will simply be ineffective for a large part of its stroke, not affecting the flow until it is nearly shut, so most of the control signal range is wasted.

Ken Irving <[email protected]>

Bob Peterson

Think again. If its really being used as a control valve, making the valve larger decreases your control capability. Usually you end up having to make the control valve smaller than line size to get good control.

The valve manufacturer can help you with proper sizing if you can't figure it out yourself.

Bob Peterson

Jaime Gonzalez

It may be that your application requires spectial trim for low noise or multistage pressure drop in orther to avoid cavitation or flashing.
These trim usually reduce the Cv of the valve, thereby requiring a larger body than would usually be required.

The body size, in it self, has very little influence on valve performance.

It is the trim size and design which rules valve characterization (relation between flow and stem or disk displacement. Your application will define whether a linear. exponential or equal percentage trim is required.
The fluid properties and the flowing parameters will define whether a single stage single orifice is required or if a multiple staging design is needed.
1/2"size control valve is very well possible provided if your pressure and temperature falls within the ANSI rating 600 psi, Moreover the Valve coefficient is almost same for 1/2" to 1 ". So the flow will not get affected because of hte change in the size from 1/2" to 1"