8-474 BLACK BUNA 90D BACK-UP RING

APG stocks the HB90474, an AS568-474 black Buna-N (Nitrile) 90 Shore A Back-Up Ring with an inside diameter of 24.94 in (633.48 mm), a cross section of 0.275 in (6.99 mm), and an outside diameter of 25.49 in (647.45 mm). A back-up ring installs on the low-pressure side of an o-ring to prevent extrusion into the clearance gap at elevated pressure.

The compound resists water, many alcohols, and hydraulic fluids. That behavior comes from the compound itself: Buna-N (Nitrile) is valued for an economical choice for high-volume maintenance programs and low compression set under sustained load. Rated temperature range runs from -40°F (-40°C) to 250°F (121.1°C) in continuous service. It is not the right choice where ketones or strong acids are present.

You will find this material specified across general industrial maintenance, construction equipment, and automotive.

Stocked as HB90474 and sold individually. Nominal inside diameter is listed as 25 inch. Check the compound against your process media, pressure and temperature before committing to a design. Not finding the exact configuration you need? APG cross-references from prints, samples and competitor part numbers.