A Brief Overview of Check Valves
The following text is the transcript of the Air Logic educational video on check valves.
Intro
Hey guys, today we’re talking about just the basics of check valves in a system. Air Logic makes inline check valves for miniature applications, but check valves are used all over the place. They’re one of the most basic valves in any hydraulic or pneumatic system. From a really simplistic standpoint, they give you flow in one direction and no flow in the other direction. So, really basic from a functionality standpoint, but when it comes down to it, there’s a whole host of different types of check valves out there. When you get into the finer details of what makes a check valve right for an application, there’s just a lot of different aspects that go into it and so a lot of different designs come out of that to fit the different needs. So, we’re going to talk about some of the things you might want to think about when you’re specifying a check valve for your application.
Nonreturn Valve Cracking Pressure
One of the first things you want to think about when you’re going to specify a check valve for your application is the cracking pressure. The cracking pressure is this term we use to say when does a check valve open. So, again, from a basic standpoint in the flow direction you’re going to get a flow through the check valve, but the cracking pressure is going to determine exactly when that starts. So, you might have a very low cracking pressure check valve that’s almost essentially a zero. Right at the zero point, you’re going to get flow. Or you might have a cracking pressure that’s much higher, 5 or 10 or 20 psi cracking pressure check valve. That means even in the flow direction, as you start applying pressure, you’re not going to get any flow in that direction until you exceed the cracking pressure. So, this is important for your application because it depends where your operating pressures are and when exactly you want that flow to occur.
Pressure Relieving Applications
So, in a pressure relieving application, you’ll have your normal operating pressure that your circuit is running at and then you use a check valve that’s above that somewhere so that if something goes wrong in the system the check valve is going to release excess pressure. It’s a really economical way to do pressure relieving versus using like a back pressure regulator or a more expensive relief valve. A check valve is usually a lot cheaper and so it’s good for high volume applications where you’re going to be using a lot of these things and you want a safety device in the circuit that’s going to protect your device from any excess pressure.
Flow Rate in Both Directions
The other thing you want to consider when you’re specifying a check valve is your flow rate in both directions. The flow rate in the forward direction is going to tell you how much flow you’re going to get in the normal operating circumstances when you’re just trying to flow through the check valve. Also, you want to consider your reverse flow. So, you might say, well I thought the check valve didn’t give you any reverse flow, right, but in practical terms, all check valves are going to make some tradeoff between how well they seal and how much back pressure they can handle and so you’ll get some amount of back flow or people will call that a leak rate in the backwards direction and so you want to consider the type of check valve and it’s specified leak rate or reverse flow for your application as well.
Other Considerations when Specifying One-Way Valves
So, then lastly there’s a couple other things you want to consider. Things like the materials that are used in the check valve, you want to make sure those are compliant for your application whether you’re running a certain type of fluid through there or a certain type of gas, you want to make sure that those materials are compliant to the ones in the check valve. And then also your connection type: what size tubing you’re using and what type of connections you’re going to have for the check valve.
Outro
So those are the basics of what to think about when you’re specifying a check valve. We’re going to have some more videos getting into more in depth topics on this so come check us out either on LinkedIn or at Air-Logic.com.
Thanks!
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