Rotary screw compressor and method for providing thrust bearing force

Abstract

A rotary compressor is provided that has a housing including a bore, bearings, a low pressure end having a low pressure inlet and a high pressure end having a high pressure outlet. A rotor is rotatably mounted by the bearings in the bore and has an end face subject to a variable axial thrust force; and a plurality of compression chambers having a low pressure, a high pressure and intermediate pressures. A piston is provided for exerting a counterbalancing force on the rotor in opposition to the axial thrust force at the high pressure end of the compressor. An intermediate pressure port is provided in communication with the intermediate pressure chamber. A conduit is connected between the piston and the intermediate pressure port which varies according to suction pressure to cause the piston to apply a variable counterbalance force on the rotor through the output range of the compressor. A method for operating a rotary screw compressor is disclosed comprising the steps of: establishing an intermediate pressure port; operating the compressor to produce a normal working output range and create varying levels of pressure within a series of intermediate pressures; and connecting the intermediate pressure port with the piston to cause the intermediate pressure to appear at the piston and exert a variable counterbalancing force on the rotor corresponding to the variable axial thrust force exerted on the rotor end face.