A FVCP is used to add clearance volume to the head end of a cylinder. A plug is pneumatically actuated to either fully open or fully close the pocket. The FVCP assembly is mounted in the head end of a cylinder.

The FVCP requires 80-100 psi of air or gas pressure to operate. Actuation of the pocket can be performed by the PLC controlling a solenoid valve. In most cases, the FVCP is normally unloaded (FVCP open), requiring air or gas pressure to load (FVCP closed).  

Data regarding FVCP designs and availability for each compressor cylinder is available in the Ariel Electronic Databook.