8-259 BLACK FKM 90D BACK-UP RING

Ordered as VBU90259, this is an AS568-259 black Viton® (FKM) 90 Shore A Back-Up Ring supplied with an inside diameter of 6.234 in (158.34 mm), a cross section of 0.139 in (3.53 mm), and an outside diameter of 6.512 in (165.4 mm). The back-up ring installs on the low-pressure side of an o-ring to prevent extrusion into the clearance gap at elevated pressure.

The material holds up against aromatic hydrocarbons, aggressive chemicals, and chlorinated solvents. That behavior comes from the compound itself: Viton® (FKM) is specified for very low compression set at elevated temperature and long service life in hot, chemically aggressive environments. Published continuous service range is -15°F (-26.1°C) to 400°F (204.4°C). Applications involving ketones and esters or low-molecular-weight organic acids call for a different compound.

Maintenance and OEM teams specify it across aerospace, oil and gas, and chemical processing.

This item is sold individually under part number VBU90259. Nominal inside diameter is listed as 6 1/4 inch. Application requirements vary, so validate compatibility with your process conditions prior to installation.