I replaced my vacuum pump's oil - your judgement please?

[robdebie]

After 16 years of on and off use, I replaced the oil in the single-stage rotary vane vacuum pump that I use for vacuum resin casting. I can't say exactly how much time the pump ran, but 5 hours total is my first estimate (100 runs of 3 minutes each). I read a warning that polyurethane does contimate vacuum oil.

This close-up shows how the oil separated after 20 hours. The top part looked like regular oil to me, then a layer that looked like engine car oil sludge, oil that has mixed with coolant or water ('mayonaise') At the bottom I see some white parts. Weird!

The lower two parts look really strange to my untrained eye. However the pump runs the same after adding fresh oil, I don't notice any difference. Since there are plenty of (hobby) car mechanics on this board, I would love to hear your judgement!

Rob

Edited April 19, 2022 by robdebie

[Ace-Garageguy]

Wish I could help you, but my old vacuum pumps are diaphragm dinosaurs, no oil.

But that certainly looks like water contamination...not surprising probably, depending on your local relative humidity.

Edited April 20, 2022 by Ace-Garageguy

[Bills72sj]

I used vacuum pumps weekly for years in my refrigeration service job. White/milky is generally caused by moisture/humidity. Particularly if you are sucking air through it.

[Oldcarfan27]

Sounds like you may need a moisture filter attached in the hose line somewhere, to trap the water that is condensing in the vacuum pressure.

Air compressors need them to keep moisture from accumulating in the lines and corroding the equipment and tools.

Just cheap insurance, regardless. 

[peteski]

1 hour ago, Oldcarfan27 said:

Sounds like you may need a moisture filter attached in the hose line somewhere, to trap the water that is condensing in the vacuum pressure.

Air compressors need them to keep moisture from accumulating in the lines and corroding the equipment and tools.

Just cheap insurance, regardless. 

So you want to add the moisture trap immediately next to the vacuum pot?

Edited April 20, 2022 by peteski

[robdebie]

Bill, Bill, Patrick and Peter, thanks all for your input!

Water contamination from moisture in the air sounds logical. Just to get an order of magnitude: at 20C and 100% humidity there are 18 grams water per 1000 liters. Humidity is on average 60-70% in my area. So at 65% its 12 grams per 1000 liters. My vacuum chamber is 9 liters, 100 runs makes 900 liters, 11 grams of water. But that would be the maximum one could extract from the air pumped through.

On the other hand, I would expect a oil-water mix (emulsion?) to split again into water with oil on top. Maybe I'll let it settle for a few more days.

A moisture trap would complicate my setup. Maybe it's easier and better to replace the oil more regularly? I bought a 1 liter can, so I can do three more replacements. Maybe every two years or so?

Rob

[Oldcarfan27]

Sounds like a reasonable solution. 

[robdebie]

After four days, it seems that more of the (supposedly) oil-water mix has separated. I'll leave it some more time to see what happens.

Rob

Edited April 22, 2022 by robdebie