I usually shoot for the 24 hour test, or at least over night on larger units. If it rises, then levels off, there's probably moisture. If it keeps rising, then a leak. Unfortunately you can't tell that with a short test.
-----Stop, step back, relax and have another go at it.-----
If you pulled it that low and only re-gained that much ; SHOOT THE GAS TO IT ! Hit 40* SAT and push liquid . There are other techniques - for a later date .
I usually shoot for the 24 hour test, or at least over night on larger units. If it rises, then levels off, there's probably moisture. If it keeps rising, then a leak. Unfortunately you can't tell that with a short test.
Great point here. If you aren't monitoring your rise over a 12/24 hour period, it's hard to get a good grasp of what it can actually tell you. On a rebuild, I don't like to see any rise over 750 microns. But I hate chasing leaks on low pressure machines a year later. It is really hard to explain to a customer when his purge is timing out 18 months after he just spent the coin on a full rebuild.
I have this from days at York, possibly a bit out-dated and probably refers to new equipment, but is an interesting starting point.
Results can be skewed by modern aromatic oils, especially with longer rise tests. If it is a positive pressure machine, has had no moisture / tube issues, what does a rise test mean ? Great, I have a vacuum leak that I will never find and is at a system condition that will never exist under normal operation !
Just my opinion.
Still do a rise test and often wonder why !?!
I have this from days at York, possibly a bit out-dated and probably refers to new equipment, but is an interesting starting point.
Results can be skewed by modern aromatic oils, especially with longer rise tests. If it is a positive pressure machine, has had no moisture / tube issues, what does a rise test mean ? Great, I have a vacuum leak that I will never find and is at a system condition that will never exist under normal operation !
Just my opinion.
Still do a rise test and often wonder why !?!
Had a Trane screw machine once that kept failing an evacuation test horribly. Put it on 100psi pressure test and would hold for days.
What was it? An o-ring. Pressure would push it out and seal. Low pressure/vacuum, it would relax and start leaking. Found it at 35psi. Started low and kept going around the machine bumping the pressure little by little. Once it did start leaking, it was like a sieve, huge bubbles.
That's my experience with evacuation tests on high pressure machines.
-----Stop, step back, relax and have another go at it.-----
I have this from days at York, possibly a bit out-dated and probably refers to new equipment, but is an interesting starting point.
Results can be skewed by modern aromatic oils, especially with longer rise tests. If it is a positive pressure machine, has had no moisture / tube issues, what does a rise test mean ? Great, I have a vacuum leak that I will never find and is at a system condition that will never exist under normal operation !
Just my opinion.
Still do a rise test and often wonder why !?!
Hello there,
Just wanted to thank you for the document - very helpful.
I'm currently studying Refrigeration at college and have found the document very informative.
Thanks,
Jacques -
Last edited by Jacquespoundsc; 06-27-2020 at 07:50 AM.
Reason: missed a word
The fact that you are looking at a 24hr standing test says you are on the right track. The most important thing I believe is a triple evacuation first, then you can commence your standing test. Anything below 500 is good - lower is even better, but a 200 to 300 rise after 24hrs is probably the most you'd want to see.
I always stress keeping a h2O tp chart on hand also. Any rise to water saturation and tapering off indicates water, continued rise indicates leaks.
Critical systems and chillers should have at least an 8 hr hold just due to temperature affects on the pressure. Max 500 micron rise in 8 hrs.
Some leaks due to warped or over torqued flanges, o-rings with excessive clearance & shaft seals may leak when in a vacuum but not under pressure.
Our industry is lacking in standards for evacuation & leak testing. A double evacuation < 500 micron, and standing hold is good insurance.
Anytime evacuation is being performed near freezing temperatures rate of evacuation should be limited and stand holds extended due to possibility of ice formation. Ice will take ~ 4x longer to evacuate due to sublimation.
Had a Trane screw machine once that kept failing an evacuation test horribly. Put it on 100psi pressure test and would hold for days.
What was it? An o-ring. Pressure would push it out and seal. Low pressure/vacuum, it would relax and start leaking. Found it at 35psi. Started low and kept going around the machine bumping the pressure little by little. Once it did start leaking, it was like a sieve, huge bubbles.
That's my experience with evacuation tests on high pressure machines.
Early style Sporlan EXVs on RTAA would do that where the wires go through the body. You can take it apart and tighten the little packing nut and use a little 515 on it.
Reply
Regular Guest
jerry142 liked this post.
Originally Posted by chillerguru
