usually have Teflon (PTFE) or PTFE coated diaphragms. PTFE is inert and does not react with most solvents and therefore is material of choice for vacuum pumps used with rotary evaporators or any other processes involved recovery of solvents such as ethanol, isopropyl alcohol, acetone, hexane, heptane and more. While PTFE pumps are expensive and more solvent can be recovered, there are much cheaper pumps using water as medium and utilizing venturi effect, where residual solvent is being mixed with water, called aspirator vacuum pumps.