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Thread: A friend of mine told me...
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10-03-2010, 07:50 PM #1
A friend of mine told me...
...that I could build a vacpump using a domestic fridge compressor. My questions are:
1) True or false
2) Good idea or not. If not, why?
Any other points you wish to raise, please do. I am learning all the time here & find these early stages of my refrigeration life challenging but very interesting so please be gentle with me.
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10-03-2010, 07:55 PM #2
Re: A friend of mine told me...
1. True
2. Better than nothing, not nearly as good as a real vacuum pump.
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10-03-2010, 08:09 PM #3
Re: A friend of mine told me...
Hi Gary.
I was just reading your refrigeration 11 thread & find your post easy to understand & informative. Keep up the good work.
If I were to try to build one using a compressor, I assume that I would need one to use on R134a & another for R600a or would that not be strictly required?
Also, any idea what sort of vacuum this method would achieve or is this like asking how long is a piece of string?
Many thanks.
Bobby.
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10-03-2010, 08:29 PM #4
Re: A friend of mine told me...
Surely a vacuum is a vacuum? But hey, I've heard that the old compressor can be used as a vac pump. You'll also need a gauge to measure the vacuum and tightness of the system. Good luck.
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10-03-2010, 08:38 PM #5
Re: A friend of mine told me...
I have never worked with R600a, so I'm not certain if that would be different.
A compressor might get to 15-20 inches of vacuum, whereas a real vacuum pump will get well over 29 inches, down into the microns. There is really no comparison... but as I said, it is better than nothing.
Way back before vacuum pumps were common, we used fridge compressors and did triple evacuations. It worked reasonably well... on the other hand, as soon as vacuum pumps became readily available, everyone ran out and bought one.
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10-03-2010, 08:47 PM #6
Re: A friend of mine told me...
Hi Gary.
The only reason I asked about different compressors for different refrigerents is to avoid any potential contamination of the system being vacced, say the system being repaired is R134a & if you are using an R600a compressor or vice versa. Or am I worrying over nothing?
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10-03-2010, 08:53 PM #7
Re: A friend of mine told me...
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10-03-2010, 09:29 PM #8
Re: A friend of mine told me...
Brian - Newton Abbot, Devon, UK
Retired March 2015
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10-03-2010, 10:01 PM #9
Re: A friend of mine told me...
You should change the oil regularly in any vac pump, this may be tricky of you are using a small hermetic compressor.
Hydrocarbons require a special safe handling certificate here in the UK and I think i'm right in saying you should be using dedicated equipment only.
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10-03-2010, 10:37 PM #10
Re: A friend of mine told me...
Get a proper vac pump if you are working for other people, they rightly expect things to be done correctly when calling in a professional.
If its some project for yourself then maybe a compressor would do but personally i'd still use a vac pump, especially on capiliary systems.
Jon
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11-03-2010, 04:57 PM #11
Re: A friend of mine told me...
The first refridgeration tech. I worked with had used a fridge comp. as a vaccumn. pump. He told me that the comp. did not last very long in this service. I would think that the comp. probably would overheat. Thus leading to its failure. C.D.
NH3 for me
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11-03-2010, 06:11 PM #12
Re: A friend of mine told me...
Thanks for the replies guys. I was pondering wheather to make one up just as a project really. I probably won't bother as it is probably a load of aggro for little benefit.
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12-03-2010, 01:48 PM #13
Re: A friend of mine told me...
'If you use a compressor as a vac pump, - hermetic compressors are piston type compressors and there will always be a gap at the top of the cylinder, even when the piston is at top dead centre. So this gas will never be pumped out of the compressor.
Therefore you can never achieve a vacuum with a low enough pressure to boil off any water in the system.
Typically water does not start to boil until you get down below 20 Torr (that is the pressure required to get water to boil at 20°C).
If the temperature is lower then the pressure has to be lower.
So get a vac pump!!!!!!!Tony
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13-03-2010, 04:40 PM #14
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