Mastercool 90065 5 CFM Vacuum Pump Two Stage features three inlet ports, an internal check valve that stops oil blowout in case of accidental power loss, and a gas ballast valve that helps prevent oil contamination caused by high moisture. Mastercool 90065 also features a two-stage design that allows lower pumping pressure resulting in a deeper ultimate vacuum and ball bearing cartridge design that reduces running temperatures by 30% and extends the life of the pump.