Check valve for vacuum relief

[peasant]

Does anyone have experience using check valves as vacuum breakers?

I need to provide a vacuum relief valve for an ASME Sec VIII pressure vessel (MAWP 30 psig) storing aqueous ammonia. I’m familiar with the API 2000 conservation vents from Groth, Protect-o-seal, Tyco, etc. but cannot use them for vacuum relief because I’m told these valves are not designed to withstand operating pressures above API 2000 ranges.

I have found VRVs that would work, but are not ideal due to their lead times or because they’re not listed in my preferred manufacturer specifications.

I have read that a check valve can be used to provide vacuum relief and want to explore this option. I envision a valve with low cracking pressure mounted vertically (open end down).

Does anyone have experience with something like this?

 

[Latexman]

I've used Check-All spring loaded check valves as a vacuum breaker before. Not in aqueous ammonia service though, but I don't see a problem with that, especially if you use a soft seat to keep odors down.

Good luck,
Latexman

 

[Chance17]

I do not view using a check valve for vacuum protection favorably.
a) What is the set pressure?
b) What is the rated capacity?
c) Can you periodically test the device?
d) What is the reliability? - will it work when it should work

If the consequence of damage is low or you can tolerate a broad range of vacuum -- then maybe a check valve could be ok.

Otherwise a calibrated device with periodic testing is indicated.

 

[don1980]

Check valves are commonly used to protect deaerators from vacuum. I haven't seen them used in other services, but I've very seldom seen any type vacuum relief valve used on a pressure vessel. In most cases, pressure vessels are designed to be inherently safe from vacuum (designed for full vac), when vacuum is possible. Also, it's often unsafe to be pulling air into a process vessel. In this particular case (aq NH3) I don't think there's a safety risk due to air entering the vessel.

The bottom line is that there's nothing that says you can't use a check valve to protect pressure vessels from vacuum. If you do, that valve needs to be regularly inspected and tested, just like other pressure relief devices. Personally, I would want to have other layers of defense too. For example, I would want to have an ESD that shuts off the source of vacuum. that's especially true if the volume is high - you didn't mention how much ammonia we're talking about. If this is a very small vessel, then I'd consider just using the check valve. If it's a leage vessel, then I'd want additional layers of protection.

 

[peasant]

I found this to be an interesting problem. I have minimal experience with aqueous ammonia but everything I could find on design of aqua ammonia storage required the storage tank to be closed from atmosphere, have a pressure set point around 30 Psig, and provide some sort of vacuum relief.

There is a prominent division between the low and high pressure tanks and relief valves. Conservation vents can't be used in my application as they are only designed for use on low pressure/atmospheric tanks and thus can't be exposed to the back pressures on a code vessel.

Finding a pressure relief valve for an ASME Sec VIII tank was of course easy, but not so for vacuum relief. Perhaps this is because pressure vessels are not susceptible to vacuum as you eluded to Don. Regardless, I was instructed to provide vacuum relief for this application.

Chance's questions proved difficult to answer. They made me realize that my issue was less about functionality and more about liability of using something not specifically designed for the application.

Fortunately I have now found a spring operated vacuum relief valve acceptable for use on ASME Sec VIII vessels that can withstand back pressures above my MAWP. It meets my other criteria (lead times, reputable manufacturer, etc.) so I believe it to be acceptable solution to my problem. Thank you to all who took time to share your thoughts.

 

[jdarco]

Peasant,

Can you share more info on the valve you found? Make and model? I sometimes get involved in similar applications and am interested in what you found.

 

[peasant]

A Kunkle Model 900 is an example of an ASME Sec VIII rated valve capable of vacuum service.