US Patent 7874820 Compressor unloading valve

A compressor apparatus (20) has a housing (22) having first (53) and second (58) ports along a flow path. One or more working elements (26; 28) cooperate with the housing (22) to define a compression path between suction (60) and discharge (62) locations along the flow path. An unloading valve (100) has a valve element (102) having a range between a first condition and a second condition, the second condition being unloaded relative to the first condition. Means (120, 160) bias the valve element toward a third condition intermediate the first and second conditions.