Patent ID: 8206132

Claim:
A compressor apparatus ( 20 ) comprising: a housing ( 22 ) having first ( 53 ) and second ( 58 ) ports along a flow path; one or more working elements ( 26 ; 28 ) cooperating with the housing ( 22 ) to define a compression path between suction ( 60 ) and discharge ( 62 ) locations along the flow path; a pressure relief valve ( 96 ) coupling the suction ( 60 ) and discharge ( 62 ) locations to relieve an overpressure in the discharge location ( 62 ) by passing working fluid from the discharge location ( 62 ) to the suction location ( 60 ); and an unloading slide valve ( 100 ) having: 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; a cylinder ( 128 ); a piston ( 124 ) in the cylinder and mechanically coupled to the valve element; a control valve ( 140 ) coupled to a headspace ( 138 ) of the cylinder to selectively expose the headspace to an oil source ( 144 ), pressure of oil in the headspace producing a force on the piston and valve element in a direction from the second condition toward the first condition; and means ( 180 , 182 ) for relieving excess pressure in the headspace by passing oil from the headspace to a low pressure location, wherein the means is in parallel with an electronically-controlled valve.