8-121 BLACK FKM 90D BACK-UP RING

The VBU90121 is an AS568-121 black Viton® (FKM) 90 Shore A Back-Up Ring measuring an inside diameter of 1.049 in (26.64 mm), a cross section of 0.103 in (2.62 mm), and an outside diameter of 1.255 in (31.88 mm). This back-up ring extends o-ring service life by supporting the seal against extrusion under high pressure.

It resists engine and transmission fluids, aromatic hydrocarbons, and aggressive chemicals. That behavior comes from the compound itself: Viton® (FKM) is widely chosen for excellent resistance to compression set and permeation, outstanding high-temperature capability. Continuous operating temperature is published at -15°F (-26.1°C) to 400°F (204.4°C). Applications involving ketones and esters or hot water and steam call for a different compound.

Maintenance and OEM teams specify it across high-temperature process equipment, oil and gas, and chemical processing.

Stocked as VBU90121 and sold individually. Unit weight is approximately 0.8183 g. Confirm chemical compatibility, pressure and temperature against your own application requirements before installing. Not finding the exact configuration you need? APG cross-references from prints, samples and competitor part numbers.