Podcast: Critical Flow Factor for a Control Valve | Episode #8

The Critical Flow Factor (Cf) is an essential number to know when sizing your valve.
In this episode of Stuff You Should Know about Oil and Gas, Kyle explains what Critical Flow Factor is and how to calculate it. 

Topics in Critical Flow Factor for Control Valve

  • Difference between Critical Flow Factor (Cf) and Flow Coefficient (Cv)
  • How Cf is used
  • A simple tool available for calculating Cf
Resources mentioned in this episode:

Podcast critical flow factor cf podcastflow valve cf podcast


Curtis: Hello and welcome to the Stuff you Should Know about Oil and Gas Production podcast. I’m your host Curtis Winkle here with Kyle Andrews. We’re going to talk today about kind of a technical term, Kyle, the Critical Flow Factor, CF. 

We’re going to talk about some bigger words, but we’ll try and make them as simple as possible to understand. So what is critical flow factor? 

Kyle: CF or critical flow factor is a coefficient that defines how pressure will recover after it drops to its lowest point inside the control valve.And this lowest point is called the vena contracta. 

Curtis: So lowest pressure point inside the valve. This is the recovery after it.

Kyle: Correct. That is the critical flow factor. 

Curtis: And why does the CF value matter? 

Kyle: All Kimray valves are globe-style valves, and each one of them has a CF value that stays consistent no matter how open the valve is.That’s unlike the CV value, which increases as the valve opens. 

So the CF value is important because it helps us size the valve correctly and know how much the valve is going to flow accurately.

Curtis: How is CF calculated? 

Kyle: The CF is calculated by dividing the downstream pressure after the vena contracta by the pressure at the vena contracta, then calculating the square root of that number.

Curtis: Okay. So it’s calculating how much pressure recovers after that vena contracta like you said at the beginning, and you could use this equation and do it by hand, but we also have a really helpful tool on our website, right? 

Kyle: Absolutely. So you can use our sizing calculator to calculate flow rate. All the CF values for each valve are included in our sizing calculator under the flow coefficients. And then also we have a great video on this.

Curtis: Yeah, super helpful tool. Encourage you to check that out at kimray.com/sizing. We’ll link to that as well as the other resources we’ve mentioned in the show notes. 

If you have further questions about CF or valve sizing, contact your local Kimray store authorized distributor to speak with one of our experts and they will be happy to walk you through that and make sure you get the right valve for your application.

Thanks for listening. We’ll catch you next time on the Stuff You Should Know about Oil and Gas Production podcast.

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