US 4,536,130 A · 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.

In a helical screw rotary compressor for a gas compression system, said compressor having:

an axially shiftable unloader slide valve for varying the capacity of the compressor,
an unload cylinder mounted to said compressor and including a reciprocating piston and defining with said cylinder fluid sealed chambers on opposite sides of said piston,
a piston rod mounted to said piston at one end and mounted to said slide valve at the other end;
whereby the application and removal of a compressed fluid to and from said chambers causes said piston to reciprocate said slide valve between full load and full unload positions and vice versa,
the improvement wherein:
said piston rod is hollow,
and wherein said compressor further comprises an indicator shaft positioned coaxially within said hollow rod,
means for mounting said indicator shaft for rotation about its axis and for preventing shaft axial movement,
an indicator pin fixedly mounted to one of said rod and said shaft and extending radially therefrom,
a helical groove formed within the other of said rod and shaft, facing said pin and receiving a radially projecting portion of said pin,
means operatively engaging said indicator shaft and responsive to rotation of said indicator shaft for at least indicating the position of the slide valve and the load/unload condition or said compressor,
and wherein said compressor further comprises;
a compressor housing, parallel bores formed within said housing for receiving intermeshed helical screw rotors, a recess within said housing opening to said bores, said slide valve being positioned within said recess for reciprocating movement therein, a bulkhead closing off one end of said unload cylinder, a bore within said bulkhead slidably and sealably receiving said hollow piston rod to permit reciprocation of said rod within said bulkhead bore, a counterbore within said bulkhead defining a high pressure injection liquid gallery for permitting high pressure liquid to be fed to the gallery, a bushing fixedly carried internally of said hollow piston rod at said bulkhead and rotatably mounting said indicator shaft, said shaft being of a diameter less than the internal diameter of the hollow piston rod, at least one radial hole extending through said hollow piston rod, a cylindrical tube concentrically surrounding said hollow piston rod and being fixed at one end to said bulkhead and being sealed at its opposite end to said hollow piston rod, terminating at that end in proximity to said slide valve bearing recess of said compressor housing and being open internally to said gallery such that irrespective of axial position of the slide valve, the high pressure injection liquid for feeds from the gallery through the interior of said hollow piston rod between said bushing and said slide valve, and fluid passage means through said hollow rod and said slide valve, and opening to an injection port on the face of the slide valve proximate to said rotor receiving bores of said compressor housing;
whereby, liquid injection can take place within the compression process, sealed from the chamber to the side of the unload cylinder piston proximate to said slide valve.

11 more elements

Simplified unloader indicator for helical screw rotary compressor

Life of this patent

Simplified unloader indicator for helical screw rotary compressor

Life of this patent

Abstract

Claims5