Value Collection ZMSCHB90251 O-ring Backup Ring Nbr Dash 8-251

Product Description

The VALUE COLLECTION ZMSCHB90251 is a rectangular-cross-section backup ring O-ring made from Nitrile Butadiene Rubber (NBR). It measures 5.143 inches inner diameter, 5.379 inches outer diameter, and 0.0468 inches thick. Rated at 90 durometer (Extra Hard), this backup ring is designed to prevent O-ring extrusion under pressure in high-load sealing applications. The NBR compound provides solid resistance to oils, fuels, and hydraulic fluids. It is installed by licensed mechanics, millwrights, plumbers, and fluid-system technicians working on industrial and commercial equipment. The temperature range of -40 to 250 degrees F makes it suitable for a wide variety of service environments.

This backup ring is used in fluid-power, hydraulic, pneumatic, and plumbing systems where standard O-rings require anti-extrusion support. The rectangular cross section seats against the low-pressure side of an O-ring groove, reducing blow-by and extending seal life under dynamic or static loading. Typical applications include cylinder rod and piston assemblies, valve bodies, manifolds, and pump housings that see sustained pressure or pressure cycling. Each package contains 5 rings, and the minimum order quantity is 1 package.

Key Features

• Rectangular cross section functions as a backup ring to prevent O-ring extrusion under pressure
• 90 durometer Extra Hard NBR construction resists deformation at elevated loads
• Operating temperature range of -40 to 250 degrees F suits most hydraulic and plumbing service conditions
• Dash 8-251 designation for straightforward cross-referencing to standard O-ring sizing charts
• NBR material offers good resistance to petroleum-based oils, hydraulic fluids, and fuels
• Packaged in quantities of 5 for convenient stocking and service-call use

Compatibility

Designed as an OEM-style replacement or service backup ring for hydraulic cylinders, pneumatic assemblies, valve bodies, and pump housings using a Dash 8-251 O-ring groove in standard SAE or AN sizing.

Installation Notes

Depressurize and lock out all hydraulic or pneumatic circuits before disassembling any fitting, cylinder, or valve body. Inspect the O-ring groove for burrs, scoring, or contamination before seating the backup ring. Install the backup ring on the low-pressure side of the O-ring within the groove; do not stretch or twist the ring during installation. Follow system manufacturer service documentation and applicable industry codes for torque and reassembly procedures.