Can someone tell me the difference between vacuum pump oil and car engine oil. How much of a difference would it make to say the ultimate end vacuum
if motor oil is used instread.
What are the physical differences between the 2 oils.microcosmicus - 30-3-2008 at 17:58
Quote:
What are the physical differences between the 2 oils.
The essential difference is that vacuum pump oil has a much lower vapor pressure.
Quote:
How much of a difference would it make to say the ultimate end vacuum if motor oil is used instead.
The pump would not be able to attain a pressure lower than the vapor pressure of the oil used.bio2 - 30-3-2008 at 18:09
Vacuum pump oil is low vapor pressure high purity
mineral oil with a narrow high boiling range something entirely different from motor oil.
Motor oil would quickly gum up a rotary vane pump and
the high viscosity would likely damage the rotor seals.
Motor oils are complex blends of various petroleum cuts
with a high percentage of additives.
Power steering fluid (clear) works in a pinch but the ultimate vacuum is dependent on the oil vapor pressure which is very low in true vacuum oil.
Some types of clear low viscosity hydraulic oils can also be used but will not pull the rated pump vacuum again due to the high vapor pressure.
Unless you want to ruin your pump stick to vacuum pump oil which is found at reasonable cost at refrigeration wholesalers. The "lab grades" are not
necessarily needed
and are much more costly.undead_alchemist - 30-3-2008 at 18:57
One place to check,
Refrigeration supply stores, or contact a refrigeration repair company.
They should have what you need.mechem - 31-3-2008 at 06:11
Thank you guys, just for future ref. I bought an old vacuum pump single stage without any oil in it. The seller drained the oil for shipping. After
filling it with engine oil it seemed to work for about an hour pulling about 28" Hg. I think some methanol vapour got in the pump as the vacuum
decreased gradually to about 25" then it started spitting out a offwhite creamy oily substance a bit like the engine filler cap, when your head gasket
has gone. I drained the creamy oil, cleaned it out and put some LHM mineral hydraulic oil I had. The stuff is green in colour and is used in Citroen
cars. THis will do to flush the pump out and to when I receive some vacuum oil.
By the way the vacuum increased to 29.5"Hg just by using the Lhm hydraulic the oil.
SO REMEMBER DO NOT USE MOTOR OIL.grind - 1-4-2008 at 13:59
The best what you can do now is to disassemble the pump completely and clean every component very carefully. Then use special vacuum oil and the pump
will work perfectly.chemrox - 1-4-2008 at 21:28
can't he clean it with a good cleaning oil? my SW 1400 was pretty rusty inside and after some reactions with corrosives and not a very good trap it
was pulling about 7 torr based on boiling ranges. I got some cleaning oil. Ran three liters through the pump which cost more than the machine. After
that it pulled down to the limits of a Bennert manometer, <1 torr. I think a good cleaning oil run for about 5-6 hours at a time would get the low
vp stuff out. Sure the metal is porous but the oil hasn't been in there that long and there was good oil in there before. The situation might not be
so dire. Definitely don't run it any more with that shit and drain it now! I found cleaning oil and regular vac pump oil, as has been mentioned
through refrigeration supplies.
