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Use of Back-Up Rings
USE OF BACK-UP RING
When the packings are used for high pressyre or the extrusion gap is too large, the heel of a packing may protrude to suffer damage (Firgure BR-1). In such cases, a back-up ring will prevent extrusion (Figure BR-2).
Back-up rings consist of synthetic resins as listed in Tabel BR-1. See Figure BR-3 to determine back-up ring requirements.
APPLICABLE PACKING TYPE
UPH, IUH, ISH
USH, OUH, OSH
IDI, ISI, IUY,
ODI, OSI, UPI
For checking extrusion of packings and back-up rings, please refer to Figure BR-3 for convenience. The amount of extrusion of back-up ring varies depending on temperature and time. Please consult a technician when application is for long hours under high temperature and pressure.
Figure BR-3 (Extrusion Limit Curve)