The rider bands are placed between the piston rings, forming a sealed enclosure. Contact between the rider band and the cylinder liner is effectively reduced to zero. As long as there is pressure in the system, the cushion layer is maintained, providing a fail-safe mechanism in the event of problems arising elsewhere in the compressor.
The FFP keeps the piston centred in the cylinder liner during operation, making the rider bands only contact the cylinder liner in the brief of time during start up and shut down. The volume of gas required is extremely small – less than 1% of the cylinder capacity, however nett capacity of the compressors is not effected.