Value Collection ZMSCHB90339 O-ring Backup Ring Nbr

Product Description

The VALUE COLLECTION ZMSCHB90339 is a rectangular-cross-section backup ring O-ring made from Nitrile Butadiene Rubber (NBR). It measures 3.274 inches inner diameter, 3.64 inches outer diameter, and 0.0625 inches thick. Rated at 90 durometer (extra hard), this backup ring is designed to prevent O-ring extrusion under pressure in dynamic and static sealing applications. The NBR compound provides solid resistance to petroleum-based oils, fuels, and hydraulic fluids. Licensed plumbers, millwrights, hydraulic system technicians, and industrial maintenance professionals install these as part of fluid-power assemblies, cylinder seals, and valve packing systems. Sold in packages of 10.

This backup ring suits applications where standard O-rings require anti-extrusion support, particularly in hydraulic cylinders, pneumatic fittings, pumps, and valve bodies operating across a wide temperature range. The Dash 8-339 designation follows standard O-ring sizing conventions, making it straightforward to cross-reference against existing seal kits and OEM specifications. The rectangular cross section provides a flat seating surface that stabilizes the primary O-ring in the gland and reduces the risk of spiral failure under cyclic loading.

Key Features

• Nitrile Butadiene Rubber (NBR) construction resists petroleum oils, hydraulic fluids, and fuels
• 90 durometer extra-hard rating minimizes O-ring extrusion in high-pressure gland designs
• Rectangular cross section provides flat, stable seating surface against the primary O-ring
• Rated for service from -40 degrees F to 250 degrees F
• Dash 8-339 designation for straightforward cross-referencing with standard seal kit specifications
• Packaged in quantities of 10 to support multi-unit service calls and inventory stocking

Compatibility

Designed as an OEM-style replacement backup ring for hydraulic, pneumatic, and fluid-power sealing systems that specify a Dash 8-339 size with a rectangular cross section and 90-durometer NBR material. Not FDA approved.

Installation Notes

Backup rings are installed by plumbers, pipefitters, hydraulic technicians, and millwrights following applicable system lockout/tagout procedures. Always depressurize and isolate the hydraulic or pneumatic circuit completely before opening any fitting, valve, or cylinder end cap. Inspect the gland dimensions to confirm the backup ring seats flat without pinching before reassembly. Avoid using sharp tools that can nick the sealing surfaces or the backup ring itself during installation.