Disappearing vac pump oil

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#1

My set up is a Hyvac-7 pump and an HF pressure pot as resin trap, and an Air Logic vac switch. The pump kept cycling on every two minutes, so after buying a leak detector and not finding any leaks, I completely disassembled every single fitting, nut, bolt, etc. and found oil in the bottom of my pressure pot.

So I fill the pump with new oil and it holds vacuum for hours. The next day I check the oil level and it’s empty, nothing on the floor, all in the pot!

Long story short, the vacuum built up in the pot is sucking the oil out of the vacuum pump! I bought a PCV from the local store and it’s lessened the effect, but I can still see oil half way up the tube leading to the pot. When the pump cycles on, it strains and then sucks all the oil back in. I tried making a tall round about vertical path for the tube but it’s still doing it, just not reaching the pot anymore.

Anyone ever experience this? The Hyvac site doesn’t say anything about a one way valve. I could make a separate catch tank for the oil, but once the pump loses oil, it becomes a vacuum leak. And I’d have to keep refilling it back in to the pump. I’d rather not engineer a catch tank, recirculator, swirl pot thingy for all this.

#2

a simple check valve between your pump and resin trap could solve your problem

#3

Thats what the pcv is, only problem is, it creates a restriction when vacuuming. The pump seems like it won’t start. And oil is still getting sucked past it, over time.

#4

I used to do HVAC work years ago and some of the vac pumps we used back then didnt have check valves so if you shut off the pump without closing the line first the evacuated system would suck the oil out of the pump (just like you’re describing). It sounds like your pump doesnt have a check valve so you either need to install a check valve or leave the pump running. The pumps can take it, we used to leave our pumps on for 24-36 hrs at a time when drying out a refrigiration system.

#5

Yeah, I was hoping the pcv would do the trick, guess I need a stronger valve.

#6

Indeed, a non-return-valve is installed in most pumps which are not running 24/7. Most pumps have them as standard, but yours seem to fail one.

#7

I am kind of glad as I was worried it might be the shaft seals or casing seals that was causing my vac leak!