8-388 BLACK FKM 90D BACK-UP RING

Ordered as VBU90388, this is an AS568-388 black Viton® (FKM) 90 Shore A Back-Up Ring with an inside diameter of 18.953 in (481.41 mm), a cross section of 0.21 in (5.33 mm), and an outside diameter of 19.373 in (492.07 mm). The back-up ring bridges the extrusion gap so the primary seal holds its shape under load.

The material holds up against many acids, aromatic hydrocarbons, and petroleum oils and fuels. That behavior comes from the compound itself: Viton® (FKM) is specified for excellent resistance to compression set and permeation, very low compression set at elevated temperature. Rated temperature range runs from -15°F (-26.1°C) to 400°F (204.4°C) in continuous service.

Maintenance and OEM teams specify it across automotive fuel systems, high-temperature process equipment, and chemical processing.

This item is sold individually under part number VBU90388. Nominal inside diameter is listed as 19 inch. Application requirements vary, so validate compatibility with your process conditions prior to installation. APG supports cross-referencing from drawings, samples and competitor numbers when a listed size is not an exact fit.