Diaphragm pumps work completely without oil which has several advantages for the user:

Less maintenance compared to other technologies saves time and money
Dry vacuum allows cleaner workplace and environment
Uncontaminated pumping of gases results in cleaner samples and no risk of oil back-streaming

Manual

Welch 2014B-01 Dryfast Diaphragm Vacuum Pump 1.2 CFM, 29.6 HG, 115V