8-355 BLACK FKM 90D BACK-UP RING

APG stocks the VBU90355, an AS568-355 black Viton® (FKM) 90 Shore A Back-Up Ring supplied with an inside diameter of 5.225 in (132.72 mm), a cross section of 0.21 in (5.33 mm), and an outside diameter of 5.645 in (143.38 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.

It resists chlorinated solvents, many acids, and aggressive chemicals. That behavior comes from the compound itself: Viton® (FKM) is widely chosen for excellent resistance to compression set and permeation, the industry benchmark where nitrile reaches its thermal limit. Service temperature is rated from -15°F (-26.1°C) through 400°F (204.4°C). Exposure to hot water and steam or ketones and esters will shorten service life.

It sees regular use in semiconductor equipment, automotive fuel systems, and chemical processing.

VBU90355 ships individually. Check the compound against your process media, pressure and temperature before committing to a design.