Patent ID: 7331767

Claim:
A method for stepless control of a reciprocating piston compressor having a suction valve which includes a valve catch, a valve seat, a sealing element positioned between the valve catch and the valve seat and biased against the valve seat to close said suction valve, an unloader which is movable to push the sealing element away from the valve seat to open the suction valve, an unloading piston, an unloading cylinder for moving the unloader, the unloading cylinder being biased away from the valve seat and against the unloading piston, and a control valve for controlling flow of actuation gas relative to the piston and the unloading cylinder, the method comprising the steps of: (a) moving the control valve to a first position wherein actuation gas is prevented from moving the unloading cylinder towards the valve seat so that the sealing element remains in contact with the valve seat to close the suction valve, and (b) moving the control valve to a second position wherein actuation gas flows to move the unloading cylinder and the unloader towards the valve seat to push the sealing element away from the valve seat and thereby open the suction valve, the actuation gas having a pressure sufficient to open the suction valve regardless of forces moving the sealing element towards the valve seat during a complete working cycle of the compressor.