Two Stage Design second stage starts pumping at a lower pressure to pull a deeper ultimate vacuum. Offset Rotary Vanes Our proven design creates the deep vacuum conditions needed for a thorough evacuation. Gas Ballast feature helps keep the pump oil clean by reducing condensation of moisture. Iso-Valve isolates pump from the system with just a 1/4 turn, making it simple to measure rate of rise. Integral Check Valve prevents pump oil from being sucked into the system if a power loss occurs. Die-Cast Aluminum housing lightweight but durable. Molded Base Durable polycarbonate base improves pump balance and minimizes vibration.