Valve Sizing: The 3 Most Important Factors in Selecting the Correct Control Valve

The process for valve sizing can be confusing. There are numerous variables in oil and gas controls, and an array of options to deal with those variables.

In this piece we’ll be covering the three most important factors in selecting a control valve:  

  1. The uses of high and low pressure valves
  2. How to use your calculated Cv
  3. Which valve to use for liquid versus gas applications

Valve Sizing: High Pressure and Low Pressure Valves

The first question you need to ask when valve sizing is “What is my pressure?”

While it sounds obvious to choose high pressure valve for high pressure application, there is another key factor you have to consider: Calculated Cv.

The Importance of Calculated Cv

The second question you need to ask when valve sizing is “What is my Cv?” Cv is the number of gallons of water that will pass through a given flow restriction at a 1 psi differential. Basically, you can think of it as the orifice size of a valve. To calculate your Cv, plug your flow conditions into the Kimray sizing calculator.  You can also use this video guide to learn how to use this sizing calculator.

Let’s look at two examples.

Example 1

  • Your pressure is less than 300 psi and your required Cv is 3 or greater.
  • In this case, a low pressure regulator should work for a gas application, while a low pressure control valve or mechanical dump valve will work for a liquid application.

Example 2

  • Your pressure is still less than 300 psi, but your required Cv is less than 3.
  • In this example. you should use a stem-guided high pressure control valve because it can meet the small Cv requirements.

This may sound counter-intuitive to use a high pressure control valve for low pressure, so let’s dig a little further…

What Calculated Cv Means for Valve Trim Sizes

Kimray low pressure valves and regulators come with 2 trim options—full port or reduced port—and might be too big for the small flow rates. Kimray 2” stem-guided high pressure control valves come with 9 trim options ranging from ¼” up to 1”. Our 1” stem-guided valve trim options range from 1/8” – ½”.

Stem-guided valves have small Cvs—from .34 to 21. They can handle low flow as well as high pressure drop applications where you have a small Cv requirement.

For larger Cvs and higher pressures, Kimray’s cage-guided high pressure control valves are full port valves with a Cv range of 28.6 to 1,091.

While our stem-guided valves are available only in 1” and 2” sizes, our cage-guided valves are available in 2" through 10".  

Can I Change My Valve Trim?

We’ve now walked through selecting a new valve. But what about if you have valves on an existing well and conditions change?

A key benefit of Kimray control valves is their versatility. For example, If you resize your valve with the new conditions and the calculated Cv does not fit the trim on your existing stem-guided valves, you can swap the trim for a different size. This will keep you from having to change your piping to fit a larger or smaller valve.