Vacuum pump mfrs state that one should change oil immediately after every evacuation to avoid negative consequences. Here is an excerpt from JB’s DV-T1 page:
“All vacuum pumps require changing oil after every use. Contaminated oil, laden with moisture and acid will damage pumps and shorten pump life. On top of that, deep vacuums cannot be achieved with contaminated oil. Maintaining clean oil in the pump ensures that your pump will operate at peak efficiency.”
I generally wait until I get back to the shop. Unless I just used it for a burnout, I often throw a micron gauge on the pump before changing oil. If it pulls down to 50 microns or less, I don’t change it. If it doesn’t, I’ve warmed the pump up enough to drain the oil and, hopefully, any moisture and contaminants with it.
I drain the oil into a 1 gallon (former) water jug. When the jug is full, I take it to the parish dump, which accepts automotive oil and the like. I have two pumps – A JB Plat DV-200N 7cfm pump that I’ve had for more than a decade. I also have a backup Robinair 5 cfm that I bought a few years ago.
I very rarely have to change the oil whilst pulling down a system, but I know that some techs encounter multiple oil changes during one evacuation.
Does anyone use a product like the JB DV-T1? What do y’all do with your used oil?