View Full Version : DIY Air Compressor using Semi hermetic compressor

01-08-2016, 01:58 AM
It seems nowadays most commercial air compressors available at the stores are a cheap induction motor spinning at 3600/3000RPM coupled to a compressor via direct drive - Noisy and possibly not long lasting.

My first attempt, some 7 years ago was to build a silent model with a hermetic freezer compressor. The thing has been running happily ever since, although the output contains oil (Fine for the garage tools, not so great to paint)

I'm thinking about upgrading the design with a Semi hermetic compressor. These have a sump with oil and I'm under the assumption dont rely on the oil circulated by the refrigerant for their lubrication, my question is: Do the valves on the head require some kind of lubrication, or am I good just ensuring the sump oil level is maintained?

The particular model I'll be using is a Prestcold PK10X0017P, 1450 RPM.

Many Thanks

The Viking
01-08-2016, 10:15 AM
Bad news I'm afraid,

All compressors designed for refrigeration will circulate oil with the refrigerant they pump around.

But to answer your question; no, no additional lubrication required. Semi-hermetic compressors have oil pumps built in (OK, not built in but rather bolted on...)


01-08-2016, 10:36 AM
But an oil separator might be a good idea to recover the lost oil.

04-08-2016, 12:10 AM
Most of the oil on my old unit came out of the oil separator mixed with water present on the (compressed) air, I'm not sure how useful recovering it would be (surely the compressor heat would boil the water again, but then it would just be re-captured...)

The compressor also comes pre loaded with Poly-oil Ester oil. What would be the best way to get rid of this? Am I right to assume I can simply remove as much as I can, add up mineral oil and do an oil change after some time of operation to remove any remaining traces of the original oil?


monkey spanners
04-08-2016, 08:26 PM
There will be a sump plug next to the oil level sight glass, suck the oil out with a tube and syringe, you can fill the new oil in the same way. Level should be between half way and just near the top of the sight glass.