8-440 BLACK FKM 90D BACK-UP RING

APG stocks the VBU90440, an AS568-440 black Viton® (FKM) 90 Shore A Back-Up Ring built to an inside diameter of 6.725 in (170.82 mm), a cross section of 0.275 in (6.99 mm), and an outside diameter of 7.275 in (184.79 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.

Viton® (FKM) is specified here for excellent resistance to compression set and permeation, very low compression set at elevated temperature. It resists many acids, engine and transmission fluids, and aromatic hydrocarbons. The material carries a published service range of -15°F (-26.1°C) to 400°F (204.4°C).

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

Stocked as VBU90440 and sold individually. Unit weight is approximately 15.85 g and nominal inside diameter is listed as 6 3/4 inch. Application requirements vary, so validate compatibility with your process conditions prior to installation. For a size or compound outside the standard catalog, APG can quote from a print or sample.