Understanding What O-Ring Squeeze Ratio is All About

10 January 2019

Imagine the following unacceptable case study. An O-Ring is seated within an equally sized groove. What’s wrong with this picture? Well, the rubber won’t compress as it’s installed. Instead, the identically sized O-Ring and circular groove create a snug fit. An effective seal can never form. To create that seal, the cross-sectional width and depth of the ring must be sized so that it’ll compress as it’s installed, and here’s why.

Creating an Effective Seal

Generally speaking, it’s true, thicker rubber loops compress and produce better seals because they’re slightly larger than the hardware they’re entering. But engineers don’t work on general principles, which is why this squeezing effect requires intelligent management. Specifically, seal integrity is governed by what’s known as an O-Ring’s squeeze ratio. It’s a figure that’s expressed as a ratio. It can be found by comparing the amount of material deformation that takes place within a rubber ring as it’s pressed into its curving groove. In engineering terms, the free-state cross-sectional density and installation deformation volume are compared and expressed as a ratio.

Deform-Proficient Rubber Matrices

Looking deeper inside the rubber loop, the specially engineered elastomer is seen to gain energy as it’s compressed during the ring seating stage. The rubber matrices squeeze together and absorb energy. In response to this action, the material pushes outwards as it’s pressed into a smaller space. Those surfaces press hard against the hardware groove. In plain English, the rubber forms a formidable seal because that absorbed energy is seeking some kind of outlet. It’s this deformation factor, the inherent elasticity of the compressed O-Ring, that’s measured as a seal’s squeeze ratio. Importantly, by selecting the correct material and ensuring that the product comes with an intelligently selected cross-sectional density, the right O-Ring squeeze ratio is singled out each and every time.

More is better, at least that’s what people are taught. For engineering professionals, that’s not always true. An optimally rated squeeze ratio creates a solid seal. Pushed beyond a certain point, though, the sealing energy is transformed into stress. Friction and seal wear occur when such stresses abide. Worse still, pinch points weaken, the walls of the groove crack, and the seal becomes compromised. To sum up, if the cross-sectional thickness is too small, excess elastic stress causes too much material deformation. Sized to match the hardware groove, seal integrity is woefully inadequate. Finally, with too much squeeze, an overly thick O-ring will weaken, or the walls of the groove will crack. Overstressed, the pinched, worn or weakened seal creates tiny pathways, gaps where pressurized fluids will leak.

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