Abstract: A noise reduction method using a muffler for connection to the air inlet of an air compressor including an imperforate, hollow housing enclosing a chamber, air inlet and outlet openings in the housing, an air inlet tube in the housing connected to the air inlet opening and an air outlet tube in the housing connected to the air outlet opening, both tubes extending over half the length of the chamber, and the openings in the distal ends of the tubes facing in the opposite directions.

Abstract: A pump assembly includes commonly driven coaxially positioned helical rotors, rotatably engageable within corresponding stators. Each combination of rotor and stator defines a pump having a different volumetric flow rate, each pump discharging to a common discharge port, thereby providing an accurately proportioned mixed fluid of two separate fluids. The rotors are integrally molded from a thermoplastic material and include an integral drive shaft suitable for interconnection to an electric motor. The two rotors are simultaneously driven by a common drive shaft and therefore produce a constant mixed ratio irrespective of rotational speed.