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Low Durometer O-Ring

The simple solution to lowering the compressive load of an O-ring is to switch to a softer O-ring material. Changing to a softer durometer material can result in up to 50% reduction in the force needed to compress an O-ring. For example, with a .070” cross sectional thickness, a 90 durometer O-ring compressed 20% needs roughly 9 to 25 pounds of compression force per linear inch. By comparison, the same size cross section but in a 70 Shore A durometer, the approximate load is 5 to 18 pounds of force per linear inch.

Compressive load challenges are most often seen in axial sealing applications. One question that comes up has to do with the amount of pressure the O-ring can withstand. The answer to this has to do with the amount of pressure the hardware substrates can withstand, and if there is a clearance gap on the hardware. If there is no clearance gap, the pressure is directly related to how much force the hardware can withstand. As soon as the pressure causes deflection in the hardware, creating a clearance gap, the O-ring is at risk for extruding. Low durometer O-rings have less tolerance for high pressure and the subsequent risk of extrusion. But, if the hardware maintains a zero clearance gap, the softer O-ring material should perform as well as the higher durometer seal material does. This, of course, assumes the plates are flat and are not causing extrusion gaps. 

Low durometer materials are readily available in the same sizes as the higher durometer materials. This means special tooling is not necessary. Additionally, chemical resistance of the elastomer is not generally impacted by the materials hardness. A careful review of the test reports will give confidence the material change will not compromise other aspects of seal function.

Parker Hannifin
O-Ring & Engineered Seals Division
2360 Palumbo Drive
Lexington, KY 40509
Ph: 859-269-2351
Fax: 859-335-5128
oesmailbox@parker.com
www.parker.com/oes