Vacuum pump question.

E

Eriksen

Joined
Sep 18, 2005
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I have moderated a compressor to a vacuum pump. Do I need to add oil regularly to this machine?
 
I would make sure you have some way of checking the oil level. it may also be a good idea to change out whatever was in there for some mineral oil or vacuum pump specific oil. some of the oils used are attracted to moisture and will damage the compressor over time. you may get away with checking the amount of oil that is in the compressor or looking at some data sheets and just doing routine oil changes adding the appropriate amount of oil each time.
 
Another thing to remember about vacuum pumps is that the maximum vacuum pressure you can obtain is limited to the vapor pressure of the most volatile components in the oil. (i.e. you'll start to boil off volatiles in the oil). Any decent vacuum pump oil won't boil even in an absolute vacuum but if you have anything dissolved in it then you may have issues. We have this problem in some of my labs where the pump is pulling a vacuum over a more volatile liquid. We address it by passing the intake through a liquid nitrogen solvent trap to freeze any volatiles and then in extreme cases we can bubble gaseous nitrogen through the pump oil to release dissolved compounds.
 
My compressor is an oil free compressor, but I need to know if the cylinders or pistons have any rubber parts which can be dried out if I use it as a vacuum pump. I have used it for spirit, epoxy and cactus juice. I know the spirit isn´t good for rubber parts so maybe i should try to spray som silicon spray into the hole where it sucks out the air?
 
Eriksen said:
My compressor is an oil free compressor, but I need to know if the cylinders or pistons have any rubber parts which can be dried out if I use it as a vacuum pump. I have used it for spirit, epoxy and cactus juice. I know the spirit isn´t good for rubber parts so maybe i should try to spray som silicon spray into the hole where it sucks out the air?
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most oil free compressors use Teflon and graphite impregnated parts to seal with. I would not try and spray any lubricant in it. I've done that and the compressors didn't last much longer afterwards. granted they where showing signs of low compression before but it seemed to hasten it's death.

Another thing to keep in mind is many compressors get some of their cooling from pumping the air, gas or whatever they where designed for. when used for vacuum they can overheat faster. also, depending on the check valve and seal arrangement, it may not work or last long pulling a vacuum.

refrigeration compressors have been proven to work well as vacuum pumps but can over heat much quicker and loose oil on the exhaust so oil levels need to be monitored. and as mentioned above, ultimate level of vacuum can be hindered by the choice of oil used
 
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