Newb question… why is a pump with oil acceptable for purge, but is not acceptable on any other system? I understand that the oil might get contaminated but why will it work for purge successfully?
What other systems is a pump with oil not acceptable?
The main consideration for roto pumps is that your using the roto to strip solvents. When stripping solvents, the concentration of solvent vapor is much higher concentration than purging extract, thus the risk of contaminating your pump oil is greater with the roto. Not sure if there is a hard sentiment or opinion against this in the community here - but as long as you follow proper pump maintenance and performing regular oil changes - you’ll be alright.
If you’re setting up a large commercial lab, with extended long term operating durations or anything like that - then a chemical duty pump with ptfe internals is the better option; but not a necessity.
Chemical duty pumps aren’t cheap but every once in a while you can find deals on eBay or Craig’s for “Welch” brand chem duty pumps. Even if they are broken, Welch has awesome customer support and will either send you a rebuild kit, or rebuild it for you at very reasonable costs vs. buying new
Also, read up on cold traps. You can put in front of your pump and if you keep it cold, you can trap solvent before it goes in your pump.