Simplified unloader indicator for helical screw rotary compressor

Abstract

The shaft coupling a reciprocating piston of a fluid motor to a slide valve shiftable longitudinally along a screw compressor housing and varying the amount of compressor suction gas returned to the suction port for varying compressor capacity constitutes an outer hollow tube having a smaller diameter indicator shaft mounted axially therein. The shaft carriers a helical V-groove on its exterior surface and a spring biased pin projecting radially inwardly from the outer tube rides in the helical groove such that, as the slide valve reciprocates, driven by the fluid motor piston, the indicator shaft is rotatably driven about its axis. Multiple cams fixed to the indicator shaft and rotatable therewith actuate juxtapositioned microswitches to indicate full load position, full unload position, and two intermediate load positions for the slide valve. The indicator shaft is directly axially connected to a potentiometer to provide an electrical analog output signal. A rotatable dial associated with the potentiometer permits calibration of the same. The hollow outer tube appropriately serves as the liquid supply conduit for liquid refrigerant or oil which is injected into the helical screw compressor working chamber via an injection port of the slide valve which port opens to the intermeshed helical screw rotors.