vacuum decay test

[nined9]

My goal is a vacuum decay test to find any leaks in our refrigeration products. is this difficult to achieve? I am new to vac systems. I have reduced the system down to the minimum- no uut or extra chamber/piping or hoses. I can finally draw down to about 30mT but when I close my isolation valve I still have a small leak (+10mT/sec). I have just a few connections and I've super re-tightened them all using teflon tape and grease. I am suspecting the connection of the vetically mounted pressure transducer. My "chamber" is only a few feet of copper pipe, all expertly brazed, ends now capped off. What could I expect as far as vac. pressure decay in a closed system?

 

[electricpete]

How about a positive air pressure test instead of vacuum test... then you can find your leaks with snoop solution

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[kenvlach]

The air pressure test is NMG for really small leaks.
Use a helium leak detector.
If that is unavailable, refigeration people usually have Freon leak detectors.

 

[MikeHalloran]

Nobody makes a perfect isolation valve or a perfect hose, either.



Mike Halloran
Pembroke Pines, FL, USA

 

[nined9]

We first do a positive nitrogen test for gross leaks.
A helium detector is unavailable. We use freon/refrigerant leak detectors -after- it is filled, the vacuum test is done beforehand to draw out moisture as well as attempt to find small leaks. I know nothing's perfect. What I'm trying to find out is how difficult is it to successfully perform a decay test? Does anyone do it? It seems as though I need to forget the decay test and just use the vac pressure data with curve fit limits. This would compensate for any system leaks I have; best case it seems, any method I use, I can only find UUT leaks that are => my system leaks. is this correct logic?

 

[EdStainless]

No hoses, no threaded joints, only metal gaskets. Good vacuum is a real pain.
Pressure decay is easier. For higher sensitivty you can test two units at once. Pressuize them, isolate from source, balance with each other and then close the balance valve. Measuring the differential between the two can be done to very sensitive levels. Don't try to measure the total system pressure decay.


= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

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