Strange Leak

[james10]

Last friday i started pressure testing a carrier 19xl centrif after rebuilding the compressor,we pressured up to 1104.1 kpa then myself and my collegue went over the system with a fine tooth comb checking for leaks using leak spray,no leaks were found however when we returned to site yesterday the pressure had dropped by 21kpa(around 3psig) so off we went looking for a leak then bingo we found a leak on the condensor releif valve reducing bush which definateley wasn't there on friday, it took both of us with a little help from my 2 foot stillsons and a scaffold tube to remove the 4" bush so basically what i'm asking is there any logic/cause behind this leak or has this happend to anyone before. like i previously said the leak wasn't there on friday

[Brian_UK]

Sealant not properly applied leaving a shortage somewhere. Then the pressure slowly working on the sealant in the thread and pushing its' way out.

[james10]

Sealant not properly applied leaving a shortage somewhere. Then the pressure slowly working on the sealant in the thread and pushing its' way out.

Sorry i should have mentioned we hadn't touched the releif valves and it hadn't leaked since the bush was fitted in 1993 when the unit was made

[Brian_UK]

Ah, OK.

So you've just been lucky that it held this long then.

[james10]

possibly

[cool runings]

.

Life's challenges

Just because it was not leaking, it is leaking now.
Life is like that, accept it and be glad you found it.

Personaly if you ask me it has been on the way out
for ages and the pressure test finished it off.

collrunnings.

.

[Grizzly]

James.
When pressurised leak testing the carrier Centrif you mention.
Do you not have to consider a bursting disk?
Or do these not have one?
Excuse my ignorance but why did you use such a high leak test pressure.
Given the normal operating pressures of a centrif.
Could this high pressure of caused the leak in the first place?
I have not worked on many myself, but those that I have.
Work at very low pressures.
Hence my question.
Cheers Grizzly
Grizzly

[chemi-cool]

What substance did you use for the leak test?
If you add a small amount of Helium to the OFN, you can find the smallest leak as the Helium molecules are very small.
As Grizzly said, there is no need to test the system at a pressure above maximum conditions.

[james10]

James.
When pressurised leak testing the carrier Centrif you mention.
Do you not have to consider a bursting disk?
Or do these not have one?
Excuse my ignorance but why did you use such a high leak test pressure.
Given the normal operating pressures of a centrif.
Could this high pressure of caused the leak in the first place?
I have not worked on many myself, but those that I have.
Work at very low pressures.
Hence my question.
Cheers Grizzly
Grizzly

These machines run on R22 there are no bursting discs on the system it has prv's, i tested the system to 1100kpa(160ish) psig as the head pressure can vary between 150-200psig i would of liked to have tested higher but i was limited by the evaporator

[james10]

What substance did you use for the leak test?
If you add a small amount of Helium to the OFN, you can find the smallest leak as the Helium molecules are very small.
As Grizzly said, there is no need to test the system at a pressure above maximum conditions.

We used OFN for the test i would like to start using helium as i've heard good things about it but untill it's use becomes more widespread to reduce setup costs i'm stuck with trusty OFN

[Grizzly]

We used OFN for the test i would like to start using helium as i've heard good things about it but untill it's use becomes more widespread to reduce setup costs i'm stuck with trusty OFN

As soon as you said the comp was on R22 James.
What you have done makes absolute sense.
OFN is fine for leak checking on R22.
I agree about the costs re Helium as well!
Also am I correct in the fact that Helium is flammable?

I have heard of guys using it on R407c where the gas molecules are smaller than Nitrogen.
But I have yet to meet someone who has actually done so!
An earlier post did say something about Nitrogen with a trace of Helium? added?
Does anyone know about this?
Grizzly

[james10]

As soon as you said the comp was on R22 James.
What you have done makes absolute sense.
OFN is fine for leak checking on R22.
I agree about the costs re Helium as well!
Also am I correct in the fact that Helium is flammable?

I have heard of guys using it on R407c where the gas molecules are smaller than Nitrogen.
But I have yet to meet someone who has actually done so!
An earlier post did say something about Nitrogen with a trace of Helium? added?
Does anyone know about this?
Grizzly

A friend of mine has a customer who insist on helium being used on their R407c not sure on flamability though, the thought of birthday ballons and candles fills me with dread

[Peter_1]

Some thoughts because the original poster is from Europe and some seems not to be aware about international regulations.

Cast irons pieces have to pressurized at 1.3 x max pressure.
LP and HP may have different test pressures, related to their max allowable pressure.

You may not add a synthetic refrigerant to trace a/the leak. He, Argon,... is allowed.

If you add to the OFN some He which penetrates better then every other gas, how will you then detect this leaking helium? Handheld He-sniffers are not available, only heavy and very expensive mass spectrometers can do the job.

Cool Runnings gave the same answer as I should gave you. Pressure test showed you the leak or bursted a weakening place in the bushing.

[james10]

Some thoughts because the original poster is from Europe and some seems not to be aware about international regulations.

Cast irons pieces have to pressurized at 1.3 x max pressure.
LP and HP may have different test pressures, related to their max allowable pressure.

You may not add a synthetic refrigerant to trace a/the leak. He, Argon,... is allowed.

If you add to the OFN some He which penetrates better then every other gas, how will you then detect this leaking helium? Handheld He-sniffers are not available, only heavy and very expensive mass spectrometers can do the job.

Cool Runnings gave the same answer as I should gave you. Pressure test showed you the leak or bursted a weakening place in the bushing.

Peter i'm aware of the current regs on testing however they are not perfect as the map x1.3 i.e R22 @55c=304psig, 304x1.3=395psig exeedes the map of my cooler which for obvious reasons i cannot go over and as i stated earlier it was not possible to isolate the cooler

[Gingerair]

Just a note, in the uk BOC sell a nitrogen/helium mix especially for pressure testing, it's alot cheaper than using pure helium. I've only ever used it in small x-size, not sure if they sell larger size bottles..

Ginge

[Peter_1]

James10, I wasn't referring to you, and you're right, regulations doesn't cover all the cases.
Therefore, there's now a questionnaire going around to all the EU-members asking if revisions have to be made.

[james10]

Therefore, there's now a questionnaire going around to all the EU-members asking if revisions have to be made.

It's about time they changed the rules a little, it's awkward trying to explain to customers why you only tested to this when they've read an article saying it should be this.

[monkey spanners]

I've had two leaks this week which turned out to be on the txv outlet, in both cases it was the first thing i checked as its a favourite leak point and got nothing, no oil either, after about two hours looking elsewhere i came back to the txv to find it covered in bubbles and now leaking well!
I can only think that temperature is a factor as in both cases the plant had just been running before testing and would have gradually warmed up while off.

Jon

[sterl]

There are hand held helium detectors out there; expensive being a relative term, they start at around $1500. US and do not require Vacuums. I have no personal experience with them but have leak detected with helium many times using a focused ultrasonic device and be assured, helium will leak from joints that won't leak with nitrogen alone. According to our Gas Guru: testing with 5% over N2 at pressures over 150 Psi the High Tech sniffers will give an indication near the leak of a higher concentration than that of the contained gas...And the better hand helds will get into the 10 PPB concentrations.

[evapcoil]

Hi Guys, please forgive my ignorance but sometimes I'm lost with the abbreviations: what OFN means?

[Grizzly]

Oxygen Free Nitrogen!
You Would never want to pressurise with oxygen. It explodes in contact with oils and greases!
Grizzly

[evapcoil]

Thank You Grizzly for the reply...
BTW, oxygen has NEVER been an option... :-)