Abstract: A screw compressor employs a piston unloader disposed in a bore remote from the compressor's working chamber. Flow communication between the bore and working chamber is through a series of unloader ports. The unloader piston has an end portion of uniform geometry which causes the physically non-overlapping unloader ports to, in effect, overlap in operation and is such that the unloader piston need not be maintained in any specific orientation within the bore in which it resides in order to unload the compressor in a continuous fashion.

Abstract: The position of a slide valve in a screw compressor in a refrigeration system is controlled using a gaseous medium sourced from the higher pressure one of two or more sources of such fluid. Preferred sources are refrigerant gas in a closed compression pocket in the working chamber of the compressor and refrigerant gas in the discharge passage downstream of the compressor's discharge port. The multiple sources of such gas are connected to a solenoid valve which, when open, permits gas to act on the piston which controls the position of the slide valve. Due to a check valve arrangement, it is always the one of the sources of gas which is at higher pressure that acts on the slide valve actuating piston. The adverse affects of refrigerant gas out-gassing and gas bubble collapse associated with use of hydraulic fluid rather than a gaseous medium to modulate compressor capacity are avoided while advantageous use is made of compressor overcompression in the control of slide valve position.

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 screw compressor employs a piston unloader which is disposed in a bore remote from the compressor's working chamber. Flow communication between the bore and working chamber is through a series of non-overlapping unloader ports. The unloader piston has a notched end face which effectively causes the unloader ports to overlap in operation. Precise and continuous capacity control of the compressor over a predetermined portion of its operating range is thereby achieved while internal high to low side gas leakage within the compressor and the clearance volume of the unloader ports is minimized. Compressor efficiency is thereby increased.

Abstract: A combination heat shield/gasket is disposed between abutting components in a reciprocating compressor. The heat shield/gasket includes strategically located protuberances, at locations where the components do not directly abut, the tips of which contact one of the components causing the heat shield/gasket to locally deflect away from the contacted component. The deflection of the heat shield/gasket at such non-abutting locations causes a dead space to be created between the component contacted by the tip of the protuberance and the heat shield/gasket. The dead space so created is a barrier to the transfer of heat, as is the heat shield/gasket itself, from the component contacted by the protruberances to the area on the side of the heat shield/gasket opposite that side on which the dead space is created.