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Droptine75
01-12-2014, 12:32 PM
Hey all, I have a question and I am hoping someone will be able to help me out.

I have notice recently that our auto purger has went from 6-10 purges every 2 hours to 25-35 purges. My question is how does a person go about checking for a leak when the system is in a vacuum? I have been going thru things in my head and about all I can come up with is smoke but I am not sure if it willbe enough to be noticed at 3 hg. Any help would be great.

Josip
01-12-2014, 02:03 PM
Hi, Droptine75 :)

welcome to RE forums ...it will be nice if you put your first post here ... http://www.refrigeration-engineer.com/forums/forumdisplay.php?72-New-to-RE

to introduce yourself to our community ... but you can do it later ...


Hey all, I have a question and I am hoping someone will be able to help me out.

I have notice recently that our auto purger has went from 6-10 purges every 2 hours to 25-35 purges. My question is how does a person go about checking for a leak when the system is in a vacuum? I have been going thru things in my head and about all I can come up with is smoke but I am not sure if it willbe enough to be noticed at 3 hg. Any help would be great.

This is not easy to answer, because, we do not know anything about your system ... but probably you have to isolate part by part of your low pressure system ... and then within isolated part increase pressure over 0 bar/psi and then you can use litmus paper or sulphur sticks depending what is more appropriate for you to use to indicate the place of your leak ...

I assume it is not possible to increase pressure over 0 bar/psi within whole system, if yes then you can organize more people to find a leak in a short time ... sometimes even with nose ...

Sometimes it is not possible i.e. easy to find a leak on low pressure i.e. vacuum side ... all seals are OK with overpressure and seal to out, but can leak in when need to seal vacuum ... this can be at compressor shaft seal ... you can try to check each compressor under vacuum ... of course you'll need to isolate one by one and then wait to see how fast your pressure rise ...there you have some diluted ammonia within oil ;)

Best regards, Josip :)

piewie
02-12-2014, 03:34 AM
There is no easy way. Josip is on the money though. Also remember to check everything attached to the system. For example if the system has screw compressors not only the shaft seals on the compressor/s but also the shaft seals on oil pumps and in fact the complete oil pump. Another favourite is the pressure relief valves.

Droptine75
04-12-2014, 12:29 PM
That is kinda what I figured. I have checked with a sulfur stick while the system isdown and had a slight positive pressure and can't find anything. The pressure relief idea is making me wonder tho. We have an ammonia sensor on our relief vent and from time to time it will alarm. We have been checking all the duel reliefs but out low side compressor has a relief without a duel valve on it. Thanks for the info and sorry about not putting my first post in the correct forum.

Segei
14-12-2014, 08:09 PM
What kind of compressors do you have?

Magoo
15-12-2014, 03:26 AM
Possibly valve stems on the low side/ vacuum area. with age and constant low temperature the stem o/rings can leak, grease stems and work them in and out a few times.
Wrap valve stems with denso tap as well. Keeps them lubricated and moisture/ice free.
Just a thought from an old person Auto-purgers are a good indicator of system tightness.
magoo

NH3LVR
15-12-2014, 07:43 PM
Probably not the case here, but I have seen it twice.
If an operator leaves a hand oil pump connected to a machine without closing the oil fill valve you can leak air into the system. The leak stops when the pressure goes positive.

RANGER1
16-12-2014, 09:44 AM
Out of interest an ultrasonic leak detector can pinpoint inward leaks in a system.
I would imagine hiring one would be possible, as we can in our neck of the woods.

PaulZ
16-12-2014, 09:53 AM
Hi Droptine
Not sure how old your plant is but I have experienced leaks under insulation due to corrosion which only became apparent when the plant tripped and the pressure increased.
These are obviously very hard to find but if you look around to see where the insulation has had the surface damaged and there is ice build up it is generally a good place to start.
As Josip has said you have no choice then to isolate parts of the system and allow the pressure to rise.
If this is a freezer plant you should be able to shut it down for a while after hours and allow the pressure to rise and use sulphur sticks as stated by Josip. The plant could be off for several hours without any loss of product temperature.
The problem is if you don't do anything about the leak you are not only sucking air in but moisture as well and this will cause other problems as well as make your plant less efficient due to ammonia's affinity with water.

Hi Magoo, I prefer the term experienced person rather then old person lol.

Regards
Paul

Føroyar
28-01-2015, 01:39 AM
First, can you smell NH3 ?
I would check the air purger, if it is not working properly you will have the gas from top of the receiver just going out in the air, is the air purger hose going into water ?

sterl
28-01-2015, 08:56 PM
If the purger is working properly and what is going to the absorber has a high percentage air content:

All of the commentary above is good stuff and an ultrasonic detector, used by somebody with some practice, will point you to the immediate area of a leak, the deeper the vacuum the better.

Do not know much about your system so....just a comment. The compressors are usually pretty easy to check for a seal leak....but one that caught me for a while was a leaking suction check valve. Oil separator and all dropped to house suction pressure throughout standby and a new seal would not overcome the pressure difference. On an idle machine: closed the suction hand valve and the machine's pressure rose instantly, then stopped, at 10" Hg in that case...