Gas operated infinite step valve

An inlet valve system for a cylinder chamber of a reciprocating compressor, comprising:

• an unloader comprising a cylindrical unloader body circumferentially disposed about a central axis of the inlet valve system and having an enclosed end opposite an open end, a central bore extending between the enclosed end and the open end within the cylindrical unloader body and defining an unloader chamber, and an inlet passage defined by the cylindrical unloader body and configured to provide fluid communication between the central bore and a location external of the cylindrical unloader body;
• a valve assembly comprising a cylindrical valve body circumferentially disposed about the central axis of the inlet valve system and having a first end opposite a second end, a plurality of first valve passages, a plurality of second valve passages, a first connective passage, a second connective passage, a plurality of inlet valve elements disposed in a plurality of valve element ports, and a central bore extending between the first end and the second end of the cylindrical valve body and along the central axis of the inlet valve system, wherein:
• the valve assembly is disposed at the open end of the cylindrical unloader body,
• the plurality of first valve passages extend between the first end of the cylindrical valve body and the first connective passage, and each of the first valve passages has a valve seating surface adjacent the first connective passage,
• the plurality of second valve passages extend between the second end of the cylindrical valve body and the first connective passage,
• the second connective passage extends between the plurality of valve element ports and the central bore of the cylindrical valve body,
• each valve element port at least partially contains a respective inlet valve element of the plurality of inlet valve elements, and
• each inlet valve element is configured to move between a closed position and an opened position by applying differential gas pressures to a front element surface and a rear element surface of the inlet valve element;
• and
• a control valve actuator comprising:
• a control valve body circumferentially disposed about the central axis of the inlet valve system and having a first end opposite a second end,
• a control valve passage of the control valve body extending along the central axis of the inlet valve system,
• a control pressure source fluidly coupled to the control valve passage,
• a control valve element disposed in the control valve passage,
• a first valve seating surface disposed on the control valve body, axially aligned with the control valve element and the control valve passage of the control valve body, and adjacent the second connective passage, and
• a second valve seating surface disposed on the cylindrical valve body, axially aligned with the control valve element and the central bore of the cylindrical valve body, and adjacent the second connective passage.

A method for unloading an inlet valve system coupled to a cylinder chamber of a reciprocating compressor, comprising:

• flowing a process fluid from an unloader, through a valve assembly, and into the cylinder chamber, wherein the valve assembly comprises a plurality of inlet valve elements, wherein each inlet valve element is disengaged with a valve seating surface in an opened position for providing the process fluid to flow through the valve assembly, wherein each inlet valve element has a front element surface and a rear element surface, and wherein the process fluid applies a first pressure to each of the front element surfaces;
• flowing a control gas to the rear element surfaces, wherein the control gas applies a second pressure to each of the rear element surfaces to maintain each of the inlet valve elements disengaged with the valve seating surface in the opened position, and wherein the second pressure is less than the first pressure;
• adjusting a control valve actuator to cease the control gas flowing to the rear element surface and flow a cylinder gas from the cylinder chamber to the rear element surface, wherein the cylinder gas applies a third pressure to each of the rear element surfaces and moves each of the inlet valve elements to engage the valve seating surfaces in a closed position, and wherein the third pressure is greater than the first pressure;
• and
• adjusting the control valve actuator to cease the cylinder gas flowing to the rear element surface and flow the control gas to the rear element surfaces, wherein the control gas applies the second pressure to each of the rear element surfaces to disengage each of the inlet valve elements from the valve seating surface in the opened position, and wherein the second pressure is less than the first pressure.