Calculation of Check Valve Cracking Pressure

[Crush]

I am trying to determine the cracking pressure for a check valve assembly that we are building and am looking for some guidance on the formula. We have an enclosed volume of moist air and we want to vent that to the atmosphere as the temperature rises. We can control the increase in temperature, so what I am looking for is the proper way to calculate the increase in pressure as the temperature changes, based on the humidity level within the enclosed space. Any assistance would be greatly appreciated.

 

[Montemayor]

Crush:

I've never heard of an equation that could calculate a check valve's cracking pressure. That doesn't mean one doesn't exist; but if I found one, I wouldn't trust it.

All the values for "cracking pressure" on check valves (the initial pressure required to lift, or open, the valve) that I've used or found have been empirical and/or best guess. The accuracy is totally dependent on the quality of the fluid, the condition of the valve, the orientation of the valve, the condition of the valve, the type of valve, etc., etc.

If I had to do what you intend, I'd obtain an empirical value by actually using a valve or prototype and testing it. Sorry I can't give you a simple and reliable equation to make this go away.

Art Montemayor
Spring, TX

 

[Crush]

Thanks for the quick response. We are going to be doing some empirical testing as well, but I was trying to get a bit more mathematical.

How about just an equation that determines the pressure increase due to a change in temperature with a given level of humidity? Something like the Ideal Gas Law, but that also incorporates the amount of moisture in the air?