Patent ID: 7887310

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; and an unloading slide valve ( 100 ) having: a single 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 single cylinder ( 128 ); a single piston ( 124 ) in the cylinder and mechanically coupled to the valve element and including a body and at least one seal ( 170 ) surrounding and carried by the body; a control valve ( 140 ; 142 ) coupled to a headspace ( 138 )of the cylinder to selectively expose the headspace to a fluid source ( 144 ), pressure of fluid 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 ( 190 , 192 ; 210 ; 220 ) for relieving excess pressure in the headspace sufficiently to avoid damage to and dislocation of the seal.