Free Floating PistonTM

The concept of FFPTM is simple, yet the implementation requires the highest standards of precision engineering.

​Non-return valves have been added to the head-end side of the piston. During the compression stroke, these valves are pushed open to allow the piston to fill with process gas under high pressure. The gas is then forced out through flow nozzles integrated into the bottom of the rider bands to from a film of pressurised gas, around 10-50 microns deep to support the weight of the piston.

The lower surface of each rider band has a profile that ensures the gas is distributed equally to create a bearing layer. The top of the rider band is machined so that when the piston is lifted, it will not contact the top of the cylinder.

free floating piston

​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.

Case Studies

Free Floating Piston

FFPTM eliminates rider band problems at BASF

BASF is one of the world's largest diversified chemical companies. At their plant in Freeport, Texas, they operate an Ingersoll Rand HSE-2-NL non-lube compressor in hydrogen service.

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