8-042 BLACK FKM 90D BACK-UP RING

Ordered as VBU90042, this is an AS568-042 black Viton® (FKM) 90 Shore A Back-Up Ring measuring an inside diameter of 3.239 in (82.27 mm), a cross section of 0.07 in (1.78 mm), and an outside diameter of 3.379 in (85.83 mm). The back-up ring extends o-ring service life by supporting the seal against extrusion under high pressure.

It resists engine and transmission fluids, many acids, and petroleum oils and fuels. That behavior comes from the compound itself: Viton® (FKM) is known for the industry benchmark where nitrile reaches its thermal limit, excellent resistance to compression set and permeation. Service temperature is rated from -15°F (-26.1°C) through 400°F (204.4°C). It should not be specified for service in hot water and steam or low-molecular-weight organic acids.

You will find this material specified across semiconductor equipment, chemical processing, and oil and gas.

Stocked as VBU90042 and sold individually. Application requirements vary, so validate compatibility with your process conditions prior to installation. APG can cross-reference from an existing part number, a drawing or a physical sample if this size is not an exact match.