Patent ID: 7959420

Claim:
An unloader system for a reciprocating compressor including a cylinder, a piston reciprocally mounted in the cylinder, a suction line selectively communicable with said cylinder through a suction valve assembly and a discharge line selectively communicable with said cylinder through a discharge valve assembly, said unloader system comprising: a) an unloader valve assembly acting as either the suction valve assembly or the discharge valve assembly of the compressor, said unloader valve assembly including: i) a valve guard and a valve seat, one of said valve guard and said valve seat being a rotatable member mounted for rotation relative to the other of said valve guard and said valve seat about an axis; ii) a valve seat passage extending through said valve seat and radially spaced from said axis, and iii) a valve member moveably mounted on said valve guard and positioned such that as said rotatable member rotates relative to said other of said valve guard and said valve seat, said valve member periodically comes into alignment with said valve seat passage; wherein iv) when said valve member is aligned with said valve seat passage pressure acts on said valve member to urge said valve member into a closed position against said valve seat and creates a retarding force resisting rotation of said valve guard; and b) means for applying a constant torque to said rotatable member during operation of the unloader system to rotate said rotatable member about said axis, said means allowing the rotation to stall if said retarding force overcomes said torque.