Use of Back-up Ring

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).

Figure BR-1

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.

Material MATERIAL SYMBOL TYPE SYMBOL APPLICABLE PACKING TYPE

Rareflon
(Tetrafluoroethylene resin) 19YF
31BF BRT2 Biascut
BRT3 Endless UPH, IUH, ISH
USH, OUH, OSH

Polyamide resin 80NP BRN2 Biascut
BRN3 Endless 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)

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