Retainers (Back-Up Rings), Hydraulic and Pneumatic, Polytetrafluoroethylene Resin, Single Turn, Static Gland
This Aerospace Standard (AS) covers scarf-cut polytetrafluoroethylene (PTFE) retainers (back-up rings) for use in static glands in accordance with AS5857. They are for use in hydraulic and pneumatic system components as anti-extrusion devices in conjunction with O-rings, packings and other elastomeric seals.
Because of the construction of groove dimensions, back-ups specific to rod applications are designated “R” - Rod (Female), back-ups specific to piston applications are designated “P” - Piston (Male).
Retainers specified herein have been designed for a temperature range of -65 °F to 275 °F (-54 °C to 135 °C) and a nominal operating pressure of 3000 psi (20.7 MPa) for code 09 material and 5000 psi (34.5 MPa) for code 10 material. Material codes are based on AMS 3678 material types.
Consideration has been made to accommodate cylinder breathing on piston applications, calculated at .002 inch/inch diameter/1,000 psi (.051 mm/mm diameter/6.9 MPa) to ensure a minimum 50% lap at -65 °F (-54 °C). This has required an increase in the diameter on certain larger sizes and a slight overlap at ambient will therefore be apparent. These parts have been designed such that the overlap at 275 °F (135 °C) will not result in axial compression of the O-rings, even in the worst tolerance stack-up situation.