The Welch 8917 Z-01 W Series 7 Direct-Drive Compact Vacuum Pump is a two-stage, rotary-vane, oil sealed vacuum pumps, with a free air displacement (FAD) 173 Lmin (6.1 CFM) at 60Hz and 141 Lmin (8.4 m3hr-1) at 50Hz. Features that improve performance or protect the pump or vacuum system under specific operating conditions include its gas ballast, anti-suck-back protection, and internal airflow cooling.