Vacuum pump oil got into my Vac oven

Hey guys I recently got vaccum pump oil in my vacuum oven while my pump was connected. How is this even possible???

Did you do a proper shut down sequence? While still pulling vac and running, Block off oven from vac, then turn off pump?

I heard a few yrs back id you dont, you risk back blowing vac oil into your oven/chamber.

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@Demontrich is right, did you just shut off the pump? What type of pump are you useing?
A long time ago a friend gave me a “bullet” brand vaccum pump.I had the pump blanked off with a valve and a tee to test it, it all went bad when I decided to give it a little air. I opened the valve(probably a little to quickly) and a massive fountin of oil erupted from the exhaust port. I have never seen oil leave a pump that violently.
Good news, ive never encountered this with any other pump!
I would reccomend that you run a cold trap between your pump and oven, That way the cold trap protects the pump, and vice versa. Have you checked your hash with a blacklight to test for oil contamination?


By flowing it from highest to lowest pressure would be my guess.
Same way you get solvent through your weed and into your recovery pot.

My understanding is that it can also make it’s way there against the pressure gradient via diffusion once you’re down at a decent vac and the probability of running into oncoming traffic is reduced.

Take home?

When using pumps with oil, you need a cold trap to keep oil out of your oil, AND terpenes out of your pump :wink:

Edit: Cascade recommends a “Forline Trap” on your rotary vane pump, rather than a Cold Trap.

It’s a Trap!


reasonable description of what probably happened and how to avoid it

doesn’t address diffusion based oil migration.


I own a foreline trap for my EM 28. I agree that a cold trap is not a good suit for a dual vane pump to stop oil from back flowing or rather migrating. My foreline trap works on the principle that under mean free path conditions that the spherical beads made of alumina present the mathematically biggest hurdle for molecules travelling in straight paths (MFP) to overcome.

The pump is continuously producing oil as gas while in operation. During MFP conditions the gas no longer flows towards areas of low pressure because effectively there is no pressure in those conditions. So any given gas molecule will travel in a random (brownian motion) direction even if it is toward the process. A forline trap then is an obstacle presented for the gas to work its way through as it condenses then evaporates many, many times and by luck then can eventually make its way out of the trap.

The problem is that they only provide protection from the consequences of pulling MFP conditions and leaving them then for hours and hours that way. They are just another piece of piping really when MFP conditions are not met. The second problem is a bit off of the OP topic but it is that my trap uses alumina spheres which tend to trap terps and themselves get soaked so to speak with process gasses that condense. This is highly undesirable because a core strength of a dual vane pump is the ability to ingest and pass process gas out through the oil. By trapping them in a foreline trap it rapidly degraded the vacuum because then it takes energy to work them out of the system via vacuum alone. Passing them into the oil makes it pretty easy to deal with and in fact a gas ballast is incorporated to facilitate this.

Also I found that the alumina beads can and will shed a bit of alumina dust which is abrasive. I understand a properly maintained trap should not but again this is a point of concern. Do you see the alumina I saw in the trap when taking it apart? Wow I was pissed I got shipped a trap with this loose abrasive in it!

A forline trap on a vac oven likely would not become effective (or needed) until a vac reading of 100 microns or less and likely much less. If the oil is indeed creeping back up the line it would be a chronic problem and be very faint at first methinks and then build over time. I suspect this issue is one of either no check valve installed and valve sequencing was not followed OR sequencing and/or a valve was installed and failed to function. I am pretty sure my foreline trap is really meant for processes like semi conductor manufacturing or vacuum welding ops that MUST ensure both a super tight vacuum and that oil does not creep up the line into the chamber.


Thank you @Beaker!


So just to clarify based off your reponse, the use of a cold trap when making shatter in a vac oven, isnt all that necessary with a rotary vane pump.

Beaker passed away brother. You won’t get a response

OMG I’m so sorry

No need to be sorry, you didn’t know. He passed away in the earlier part of the year.


In reponse to use of cold trap for rotary vane pumps, I’m using a 11.3cfm bvv pump with a 1.9 and .9 AI ovens. I’m not using a cold trap as that was recommended to me from a consultant. It’s been working great so far as long as you do frequent oil changes. The only problem I’m seeing is corrosion on the bolt/nut on the oil inlet port. Any suggestions or concerns about the corrosion?

Get a one way valve there very cheap. I use to have a “genius” who worked for me do it all the time. Bhogart sells kf25 ones

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How will this help with the corrosion on the nut?

Its to stop oil from getting in your oven. I have no idea about or how your getting corrosion, if its not effecting your vacuum depth who cares about it

I have a Y connection so I can run 2 ovens to one pump as necessary. As for the corrosion, it hasnt affected the pump performance yet, but I just want to keep it that way. How frequently do you do pump oil changes?

I dont eun ovens and assuming theres not tons of alcohol ( if your doing etho products) i use to change mine about once every week or two. I only do distilation now and i change my oil every 2 second passes unless i notice i higher vac level than usual. I also use a roughing pump that take the brunt of all terps etc. get the baffle from Bhogart or im wire you can find one cheaper if tou look then just run a Y after the baffle. Just noticed you already run a Y

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so long as you’re not using a lot of ethanol, there is no absolute need for a cold trap.

ie: you’re not winterizing with ethanol & you’re not making EHO

however, see “holy water”, which was stuff that didn’t go into the pump because of a cold trap.

the “terpshine” from the cold -trap when purging winterized BHO is also a joy :wink:

Happened to me.

You have to close the vacuum inlet valve on the oven before you shut off the vac pump. Have to.

If you don’t, suddenly that large oven space full of vacuum pulls against the pump when the pump suddenly stops pulling against it, and whatever is in the pump gets sucked backwards into the oven.

I was more fortunate, I use one of those cheap blue and white Chinese water aspirators (we call them R2-D2s) so I only got water in the oven. We are ethanol-only so we don’t have to oven quite as hard as the butane bois so no need for a fancy vac pump. The water catches the few volatiles.

If the pump fails its cheap to get another one from my lifelong new eternal best friend LanPhanDan. They are actually surprisingly robust. We beat the hell out of them like a rented droid and they take it.


Not needing as good a vacuum as the butane bois for etoh makes no sense to me. When I purge etoh laden absolutes I need a harder aka higher vac to achieve lower purge temps then I would with hydrocarbon oleoresins… ime

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