These combination rotary vane/diaphragm vacuum pumps are designed for use with acids and other harsh chemicals including TFA, TFA by-products and acetonitrile. The pumps consist of a two-stage rotary vane pump and two-stage, chemically-resistant diaphragm pump. The rotary vane pump provides the deep vacuum required for good freeze drying results and other evaporation needs. The diaphragm pump removes the condensable vapors in the rotary vane pump before they can contaminate the oil, thus extending the life of the oil and ultimately the life of the pump. Pump oil lasts up to 10 times longer than in conventional rotary vane pumps.