Mr O-Ring 391 EPDM O-Ring 22in ID, Pack of 5 - Weather Resistant

In this review the Mr O-Ring 391 EPDM O-Ring (pack of 5) is evaluated for users who need reliable, weather-resistant sealing in plumbing, automotive, or industrial applications. The bottom line: this 70A durometer EPDM ring is best for installations that demand ozone, sunlight and heat resistance up to 125C while remaining flexible at low temperatures, offering consistent nominal and actual dimensions for predictable fits. It is a practical choice when long shelf-life and compatibility with water, brake fluids, dilute acids and steam are priorities.

Key Features

• Material and Durometer: 70A EPDM compound provides a balance of flexibility and firmness that suits static and moderate dynamic seals.
• Nominal and Actual Size: Nominal 22in ID with precise actual measurements ensures a closer-than-average fit for applications requiring dimensional accuracy.
• Chemical Compatibility: Performs well with water, alcohols, ketones, dilute acids and alkalis, and phosphate ester based hydraulic fluids for broad use.
• Temperature Range: Rated from -55C to 125C for reliable sealing from cold environments up to high service temperatures.
• Durability: Excellent resistance to ozone, sunlight and weathering gives confidence for outdoor or exposed installations.
• Pack Size: Supplied as a pack of 5 to cover multiple seals or spares for maintenance tasks.

Who It's For

This o-ring is aimed at maintenance technicians, plumbers, and DIYers who need a robust EPDM seal for water systems, brake fluid service, low-pressure hydraulic components, or outdoor equipment exposed to weather and ozone. Its 70A hardness and measured dimensions make it suitable where a predictable compression and seal profile matter.

Those needing resistance to petroleum-based oils, aggressive hydrocarbons, or very high-pressure rotary seals should look elsewhere; EPDM is not recommended for general exposure to mineral oils and some non-polar solvents. If a softer or harder compound is required outside the 70A range, consider a different material or durometer.

Pros & Cons

Pros

• Good weather and ozone resistance, making it durable for outdoor use.
• Wide usable temperature range from -55C to 125C for versatile deployments.
• Accurate actual dimensions (21.955in ID, 22.375in OD) reduce fit surprises during installation.
• Pack of 5 provides spares for maintenance or multiple installations.

Cons

• Not compatible with many petroleum-based oils, so it is not universal for all automotive or industrial fluid systems.
• 70A hardness may be firmer than desired for very low-pressure or delicate sealing surfaces.

Specifications

Brand	Mr O-Ring
Material	391 EPDM
Durometer	70A
Nominal Dimensions	22in ID, 22-3/8in OD, 3/16in CS
Actual Dimensions	21.955in ID, 22.375in OD, 0.210in CS
Metric Dimensions	557.66 mm ID, 568.32 mm OD, 5.33 mm CS
Temperature Range	-55C to 125C

Our Verdict

The Mr O-Ring 391 EPDM 70A in a pack of 5 is a strong, value-oriented choice for anyone needing weatherproof, ozone-resistant seals with accurate nominal and actual sizes. It is particularly good for water systems, low-pressure hydraulics and outdoor equipment, but those needing oil resistance or a different hardness should choose another compound.

Frequently Asked Questions

Are these o-rings suitable for steam?
Yes, the material can handle steam exposure up to 204.4C in short-term conditions, though continuous high-temperature steam service should be evaluated case by case.

Will these resist automotive brake fluid?
They are compatible with many automotive brake fluids and phosphate ester based hydraulic fluids as stated, making them suitable for related sealing tasks.

How long will they store without degrading?
These EPDM o-rings have an effectively unlimited shelf-life when stored away from direct sunlight and extreme temperatures.