A typical hvac evacuation vacuum pump…how many inches of mercury will these pull? I need a vacuum pump which will move around 6cfm and pull 24″ of vacuum (not concurrently). It’s looks like the hvac ones will work, but the mfr’s don’t list the amount of vacuum their units can generate.
Don’t suppose anybody has a used one they want to part with…
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HVAC systems should have a vacuum of approx. 500 microns (about 29.7 in Hg) before charging with refrigerant. What is your application? Ebay has many for sale but a new 7.5 cfm pump will run about $400.
I have a couple hvac pumps. but when I first started I would use a old refrigerator compressor till it burn up. work good.
This is for some figerglass work. You apply vacuum to the layup to suck all the air out of the resin. I was looking at the units on ebay (much cheaper than new) but most were not listing the vacuum level. I even went to the mfr. sites and they wern't listing it there either. It looks like I have the pump type picked out, now I just have to find one for the right price. Thanks for the help guys!
At just 24" Hg needed, an air compressor will work, but you will have to fab something over the intakes for the pickup. The 6cfm you quote is way too much for typical hvac, which are up to 2 cfm but need to pull less than 50 microns (29.9+ Hg when barometer is 30). An old chrysler dual cylinder air conditioner compressor wioul work nicely.
Where are you located (too many here do not put anything in their member profile) , if in Pacific NW (Renton WA) come by when nearby and I'm sure I've got something in one of the back sheds that will work for you free.
If memory is still good, Vacuum pulled capability for air compressors is very roughly 30"Hg - 30*(1/compression ratio), so if a compressor can put out 147 psi, it will be able to pull close to 27" Hg. There's a couple other factors in that equation, but too lazy to look up the exact formula tonight, but a typical air compressor is over 24" Hg anyway.
I still use an old refrigerator compressor to evacuate HVAC systems.
Maybe you could raid several old refrigerators and parallel the compressors to get more cfm capacity? Old refrigerator compressors should easily pull 24 inches of mercury in vacuum. Do add refrigerant oil occasionally to the suction side of the compressor to lube it.
Frank DuVal
I actually live in the midwest, so I don't think I'll be stopping by any day soo! lol
With a refrigerator compressor, is it as easy as it seems? You just pull the unit out, wire it up and then add a oiler? The motor and compressor is one unit right?
as easy as it seems
Yeah, it is, all you gotta do is add a switch in place of the thermostat and solder on a fitting to the typical 1/4" tubing. For your application, you likely have big leaks tp the F/G cover, which is why you need 6 cfm, you are gonna need like 10 or more old fridges for that - I don't even have that many <G>