The purpose of this standard is to provide the missile hydraulic and pneumatic component designer with information learned, tested and substantiated in correction of problems and failures experienced with seals that are subject to the unique requirements of missile static storage and subsequent dynamic operational conditions. Missile hydraulic and pneumatic component designers have been handicapped by the absence of concise design criteria for two difficult sealing conditions usually existing in missile applications as follows: Static pressure condition - Low pressure for long periods in a cyclic temperature environment (i.e., long term storage requirements). Dynamic pressure condition - High pressures suddenly applied in an extreme temperature environment (i.e., operational firing requirement).
This SAE Aerospace Recommended Practice (ARP) provides an overview of the various types of polytetrafluoroethylene (PTFE and TFE) back up rings for hydraulic and pneumatic fluid power applications, including their advantages and disadvantages.
The backup ring is defined. The various types designed for use with O-rings in MIL-G-5514 packing glands, and MS33566 and MS21344 universal fitting installations are described. Guidelines are included for selecting backup rings and backup ring materials. Backup ring installation procedures and precautions are described.