Synchronized unloader system and method for a gas compressor

An unloader system for a reciprocating compressor including a cylinder, a piston reciprocably mounted in the cylinder, a rotatable crankshaft connected to the piston, a suction line, a discharge line, a suction valve assembly and a discharge valve assembly for selectively communicating the suction and discharge lines respectively with the compressor cylinder, which unloader system comprises:

• (a) an unloader valve assembly having a valve seat with multiple seat passages arrayed in a seat passage circle, a valve guard and a plurality of valve members movably mounted on the valve guard between open and closed positions with respect to said seat passages, said valve members being arrayed in a valve circle, said valve cage being rotatably mounted on said valve seat about a rotational axis concentric with said seat passage circle and said valve circle;
• (b) a stepper motor mounted on said valve cap coaxially with respect to said valve seat;
• (c) a coupling drivingly connecting said stepper motor to said valve guard;
• and
• (d) a controller including means for incrementing said stepper motor in successive cycles corresponding to the angular spacing of said valves in synchronization with said compressor crankshaft, each said incremental rotation of said stepper motor corresponding to a complete revolution of said crankshaft and consisting of a first rotation from a loaded position with each said valve member aligned with a respective seat passage to an unloaded position with each said valve member being located between a respective pair of adjacent seat passages, and a second rotational movement from said unloaded positions to loaded positions aligned with respective, adjacent seat passages.

A method of unloading a reciprocating compressor including a cylinder, a piston reciprocably mounted in the cylinder, a rotatable crankshaft connected to the piston, a suction line, a discharge line, a suction valve assembly and a discharge valve assembly for selectively communicating the suction and discharge lines respectively with the compressor cylinder, which unloader method comprises the steps of:

• (a) providing an unloader valve assembly with a valve guard, a valve seat having a plurality of seat passages arrayed in a seat passage circle, a plurality of valve members movably mounted on the valve guard in a valve circle and movable between open and closed positions with respect to the seat passages;
• (b) rotatably mounting the guard on the valve seat;
• (c) generating a signal corresponding to an angular orientation of said compressor crankshaft;
• (d) providing a stepper motor;
• (e) drivingly connecting said stepper motor to said unloader valve assembly guard;
• (f) rotating said valve assembly guard by said stepper motor by an angular increment corresponding to the angular spacing between an adjacent pair of said valve members in response to a revolution of said crankshaft;
• (g) rotating said valve guard for each incremental rotation by a first phase corresponding to approximately one-half the angular spacing of said valve members and by a second phase corresponding to approximately one-half the angular spacing between said valve members;
• (h) positioning said valve members between respective, adjacent pairs of valve seats with said first rotation phase;
• and
• (i) aligning said valve members with respective seat passages adjacent to their previously-aligned seat passages with said second rotation phase.