Podcast: Why is Valve CV So Important? Episode # 3

In this episode of Stuff You Should Know about Oil and Gas, Kyle Andrews, Product Applications Trainer at Kimray, explains the importance of control valve CV.

Topics in Valve CV

  • Why is CV so important,
  • How do you determine CV?
  • Common challenges related to incorrect CV calculation

Resources mentioned in this episode:


Curtis: We’re talking today about month after month our highest trafficked blog, and that is about CV. What is CV?

So, Kyle why don’t we try to just kind of unpack this and I’ll hit you with some questions. So first of all what is CV? Give us a brief definition.

Kyle: CV is the number of gallons per minute of water that will flow across a given orifice with a one PSI differential. That is the technical definition of it, but basically you can think of it as a way that we designate the size of a certain trim or the flow capability of a certain trim.

And the way we size our trim or rate the CV for each trim size that we have is we rate it at a percentage open. So, let’s just take a half inch trim for example. So, half inch trim will have a CV rating at 10% open 20, 30, 40, 50 and so on. It’ll have a different CV rating at each of those percentage open.

The further open the trim is, the higher the CV number will be because it’s able to flow more gallons per minute if it’s more open because that’s got a bigger opening.

Curtis: Okay. So, why is it so important in an oil and gas production?

Kyle: This is important because when you’re sizing a valve it lets you know how much flow you’re going to get across the valve.

If you’re using our sizing calculator on our website, you input your process conditions. So, that’s upstream and downstream pressure and temperature. Your flow rate and those inputs can then calculate a required CV. So, that’s telling you with the conditions that you input, you’ll need to use a valve with at least this CV.

And once you run through that calculation and it spits out a calculated CV, you can then take that and select the correct size of trim. If it’s a high pressure control valve or select the correct size regulator that way. If you’re undersized or oversized, the valve won’t operate correctly.

But when you use our sizing calculator and you select the right size trim to fit that calculated CV, the valve will operate correctly.

Curtis: Yeah, that’s a really good tool, the size calculator, just go to Kimray.com/sizing and we’ve got it for gas and we have it for liquid as well.

I’m assuming you point people there quite a bit?

Kyle: Oh yeah, all the time. If people aren’t familiar with using the sizing calculator, they can get ahold of our applications group and we can walk you through how to use it. There’s also a good video on how to use it. Once you use it a few times, it’s pretty easy.

And then one cool feature about it is there’s a product selector. So, after you calculate your CV at the bottom of the page, you can put in a few more inputs, such as max working pressure, and then the CV range you’ll want to stay within and then you can hit find product. The product finder will pull up all of the product that fits that application.

So, it’ll only pull up product that is sized for that CV that you calculated in the sizing calculator.

Curtis: Yeah, now that includes trim type?

Kyle: Trim type is a filter that you can put on it. You can filter by trim, type, trim size, body connection, and size. There are a lot of different filters that you can whittle down your choices, because it’ll give you everything that fits that calculated CV.

So, it’s probably going be a quite a few options in the beginning until you start using those filters to narrow down your choices into what you really need.

Curtis: Gotcha. So, this is an area that we see producers have challenges with. I think a lot of times, we’ll have aging wells and the CV can change. Is that correct?

Kyle: Yeah, it’s never going to remain the same. Flow conditions are always changing. And you have to be willing to have your valve be flexible too. And if you initially size a valve with a certain flow rate and then over time that flow rate drops off or maybe you’re adding wells on.

So, their flow rate increases either way. You have to be able to adjust your valves, and it’s not always going to be one trim size. One size is not always going to fit every application and you have to be able to resize the valve with your new conditions and make sure that the valve you have is still the correct valve, or you may need to increase or decrease the trim size.

Curtis: How often does that happen? People have to change out.

Kyle: Well the need for people to have to change out their trim happens often. A lot of the times though, people just keep the existing trim in there and kind of deal with the problems that it causes. It’s really not the most efficient way to do it.

Changing your trim size and making sure that you have the correct size trim is pretty critical. Especially in gas regulation.

It’s not so critical in a liquid dump valve application. For example, if you’re using a high pressure control valve as a liquid dump valve or if your valve is oversized, it’s not as big of a deal. You may get some hammering or some chatter.

But if you’re oversized or undersized in gas regulation, it’s not going to be good. The pressure is going to build. Valves are going to try to make an adjustment and it’s going to make too much of an adjustment when it opens because it’s too large. Then it’s going to slam back shut and you’re not going to have a steady set point or pressure that you’re trying to control.

It’s going to be all over the place.

Curtis: So, if somebody is seeing that in that situation, what are their options? Change the whole valve out?

Kyle: No, if you’re using our high pressure control valve, there’s a lot of different trim options. For example, our stem guided valves, which are available in one and two inch, there’s a lot of different trim options.

I think in our one inch there’s 16 or 17 trims and then our two inch, I think there’s 14 or 15 different trim sizes and types. So, there is a lot of flexibility within that valve.

And our larger valves are our cage guided valves. There is the full port version and then there’s a reduced port. So, there is only one option to downsize without changing the body in our cage guided valves.

Curtis: All right. Any other tips or common problems you see around a CV values, Kyle?

Kyle: People when they’re sizing valves there’s three different trim types.

There’s nominal or linear, can be known as either one, there’s snap trim or quick opening trim, and then there’s equal percentage trim. People get confused about when to use each one of those and in what applications.

And then also the sizing that you want to do for each of those is different. So for a rule of thumb, we say you want a size of out between 20% and 80% of stem travel or valve capacity.

That just gives you room on either end if conditions change. It gives you a little bit of wiggle room on both ends. You want 20% on both ends, if you size between 20% and 80%. And so what I see some people doing is, people will size at 80%, on equal percentage trim, they’re in there within that 20% to 80%, but 80% for equal percentage trim is at the upper end of the flow curve for that trim.

So, the way that equal percentage trims opens is very slow. And then at about 60% to 70%, it ramps up on a steep curve. So you don’t really have the best control after 60%. On equal percentage trim, you really want to keep it or at least below 60%.

Around 20% to 60% is the ideal range for equal percentage trim.

So, looking at the flow curve for each trim, size and type when you are selecting a trim important. And that’s where I see a lot of people go wrong. They say okay, I’m within 20% to 80% I’m good, but if you know it’s equal percentage trim and you’re regulating gas, you may get some fluctuations and set point just because the valve is making a 10% move in stem travel, but you’re getting 25% flow change as far as the valve capacity.

So it’s important to take note of that and look at the valve and trim flow curves for each size.

Curtis: Very good, we’ve got a previous podcast on the three types of valve trim that you can check out as well. Okay, I appreciate your time Kyle. We’ll put links to the products and resources mentioned in this episode in the show notes, and we will catch you next time on Stuff You Should Know about Oil and Gas.

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