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.
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?
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
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
Yes I am making EHO. There is about 5-10% ethanol left in the oil solution when put into the oven. So If I’m putting 1000g into the oven there could be approx 100g of Ethanol flowing into the pump.
a rotoray vane pump will not appreciate that. certainly not long term.
I’d say your consultant was wrong. unless you’re running a diaphragm pump or an aspirator, you should have a cold trap on your oven when processing EHO.
Isnt the rotary vane just going to pull some of the solvent out of the cold trap anyway? Even if I do frequent oil changes (1x-2x a week) is it still a problem to not use a cold trap?
