Patent ID: 6422846
Filing Date: 2002-07-23
Classification: F04C

Abstract:
In a multi-rotor screw machine having a rotor housing and a discharge housing secured to said rotor housing, a plurality of rotors located in said rotor housing with one of said rotors being a sun rotor having an axis of rotation and driving and coacting with each of the other plurality of rotors in a paired relationship with each pair having an axial and a radial discharge, structure for unloading and controlling capacity in said screw machine comprising:said sun rotor having an end facing said discharge housing; an annular seal located on said end of said sun rotor in a sealing relationship with said discharge housing; said seal extending axially further towards said discharge housing than a portion of said end radially inward of said seal and at least partially forming a low pressure chamber; a fluid path connecting said chamber to suction pressure in said screw machine; a pair of recesses formed in said discharge housing and each of said recesses being partially coextensive with said end of said sun rotor and said seal; a pair of slide valves with each of said slide valves having a slider reciprocatable in a corresponding one of said recesses; means for individually selectively moving said slide valves in said recesses; each of said slide valves having a full load position wherein said sliders and said discharge housing form a full 360Â° sealing relationship with said annular seal and form a part of the corresponding axial discharge; and when said slide valves move from their full load position they restrict said axial discharge and permit fluid communication across said seal to cause unloading and to delay the start of compression with the positions of said slide valves determining the degree of restriction of said axial discharge and the degree of delaying the start of compression.