Combined pressure matching and capacity control slide valve assembly for helical screw rotary machine

Claim 1

In a positive displacement helical screw rotary machine for functioning either as a compressor or an expander and including a casing provided with a barrel portion defined by intersecting bores, with coplanar axes located between axially spaced end walls and having inlet and outlet ports in communication with the bores at opposite ends, helical screw rotors each having grooves and lands being mounted for rotation within respective bores with the lands and grooves of respective rotors intermeshed, an axially extending recess provided within the barrel portion of the casing in open communication with said bores and a slide valve member mounted for axial sliding within the recess with the inner face of the slide valve member being complementary to the envelope of that portion of the bores of the casing structure confronted by the opening of the recess and with the slide valve member communicating the bore portion of the casing structure with the slide valve member in sealing relation with the confronting rotor structure, the outlet port having at least a portion located in the barrel portion of the casing structure, with the slide valve member being movable between extreme positions in which the outlet port is open and closed, said slide valve member being of sufficient length to cover the entire remaining length of the confronting portion of the rotor structure throughout the range of movement of the slide valve member between its extreme positions, pressure sensing means provided adjacent to the end of the slide valve member closing off the outlet port to the closed thread for sensing the pressure of the working fluid within the closed thread just upstream from the outlet port, means for comparing the pressure of the outlet port to the closed thread pressure at said outlet port, and means for automatically shifting the slide valve axially to equalize these pressures to prevent undercompression or overcompression of the working fluid when the unit is functioning as a compressor and for preventing underexpansion or overexpansion of the working fluid when the unit is functioning as an expander to maximize machine efficiency in respective modes, the improvement residing in an axial bore within the slide valve member, a plurality of longitudinally spaced overflow channels in the slide valve member inner face communicating the inner face partially defining the envelope of the intermeshed screw rotors to said axial bore and means communicating the axial bore to the inlet port of said machine, a cylindrical volumetric capacity control valve body movably disposed within said slide valve member bore in sealing fashion therewith and including means responsive to shifting of the valve body for selectively covering and uncovering the overflow channels and communicating the slide valve member bore to the working chamber bearing the intermeshed helical screw rotors, and means for effecting control movement of said valve body relative to said valve member bore.