Abstract: Apparatus as disposed internal of a refrigeration screw compressor which, upon compressor shutdown, shuts off the flow of oil injected into the compressor's working chamber and the oil which is directed to the compressor rotor bearings and which at compressor startup opens oil flow to those locations by the use of ambient internal compressor conditions that inherently exist at those respective times. The operation of the apparatus is therefore "fail safe" and the need for external oil flow cutoff valving and the need to monitor and/or prove oil flow within the compressor is eliminated.

Abstract: A multi-cylinder reciprocating compressor is disclosed which is provided with an unloader valve for blocking the flow of suction gas to at least one of the cylinders to reduce the compressor capacity. The unloader valve is disposed at one end of a cylinder bank and comprises an unloader piston and an unloader port which is an integral part of the cylinder bank. A chamber in which the unloader piston and unloader port are located is formed in the cylinder bank with its axial center in parallel alignment with the axial center of all the cylinders in that bank. This improved efficiency, facilitates ease of manufacture, and reduces associated costs.