Control Valve Sizing: 7 Tips and Tricks from a Mechanical Engineer

You know how to choose the right type of control valve for your processing application. The style of valve you choose depends on your application, your industry, the preferences of your plant, and your past experiences. The question is – do you know how to size it correctly?

If you don’t size your control valves correctly, the efficiency of your operation will be negatively affected. Sizing your control valves can be complicated but it doesn’t have to be.

Keep reading to learn more about control valve sizing and for 7 tips and tricks from a mechanical engineer to get you started.

The Basics of Control Valve Sizing

It’s essential to choose a properly sized control valve for your application. This ensures you have process control for your liquid, gas, or multiphase fluid.

The goal is to use as much of a valve’s control range as you can while maintaining a reasonable safety factor.

If a valve is undersized, it can’t pass the required flow. Most of the time, valves are oversized. When this happens, the valve is too sensitive to operating conditions.

Changes in valve position can cause unwanted changes in flow. Essentially, the valve will struggle to adjust to the required flow.

Tips and Tricks for Sizing Your Control Valves 

Now that you know a little more about the importance of sizing your control valves, let’s get started. We’ve put together our best tips and tricks for sizing control valves. 

1. Always consult a professional who can analyze your application to make sure you are using the right type of valve and that it is sized appropriately. This should be a qualified valve engineer.
2. Never use a control valve that is larger than the line size or less than half the line size. This is considered poor piping practice.
3. Sizing a control valve to operate 20-80% open at the maximum required flow and at least 20% open at the minimum required flow will give you the best control.
4. A properly sized globe valve will be one size smaller than the line.
5. A properly size full or segment ball and high-performance butterfly valve will be two sizes smaller than the line.
6. If the pressure differential across a valve decreases as the flow rate increases, an equal percentage control valve should be used. This is also true when the process gain decreases as the flow rate increases in control loops. In other cases, a linear control valve should be used. 
7. A valve may have the wrong flow characteristic if a set of loop tuning parameters works only at one end of the control range, but not the other. 

For More Information

If you need help with control valve sizing, we are here for you. Properly sizIng your valves is essential for the safety and efficacy of your operation. Both undersizing and oversizing can have unintended consequences.

Check out our technical resources guide here or contact us for more information about our products and for help choosing the best fit for your application.