8-155 BLACK BUNA 90D BACK-UP RING

Ordered as HB90155, this is an AS568-155 black Buna-N (Nitrile) 90 Shore A Back-Up Ring with an inside diameter of 3.987 in (101.27 mm), a cross section of 0.103 in (2.62 mm), and an outside diameter of 4.193 in (106.5 mm). The back-up ring installs on the low-pressure side of an o-ring to prevent extrusion into the clearance gap at elevated pressure.

This material stands up to water, greases and lubricants, and propane and butane. That behavior comes from the compound itself: Buna-N (Nitrile) delivers low compression set under sustained load, strong abrasion and tear resistance. Published continuous service range is -40°F (-40°C) to 250°F (121.1°C). It is not the right choice where ketones or strong acids are present.

It sees regular use in construction equipment, agricultural equipment, and general industrial maintenance.

Stocked as HB90155 and sold individually. Unit weight is approximately 1.179 g and nominal inside diameter is listed as 4 inch. Confirm chemical compatibility, pressure and temperature against your own application requirements before installing. For a size or compound outside the standard catalog, APG can quote from a print or sample.