When choosing to install an O-ring seal, squeeze ratios are incredibly important. Understanding the degree to which a seal is squeezed by its mating hardware is the first step in selecting the appropriate material and design for any application.
The O-Ring Squeeze
Expressed as a percentage of free-state, cross-sectional thickness, “squeeze” is actually a measurement of the amount of deformation to the seal when it comes in contact with its mating hardware. O-rings have inherent elasticity, and it’s this elasticity resulting from contact that blocks the flow of gasses, liquids, and other substrates between the seals.
Selecting the Right Squeeze Ratio
In general, the higher the percentage of “squeeze,” the tighter the seal. That doesn’t mean, however, that the highest squeeze ratios are always necessary (or even best) for every application. Other factors to consider include:
Mating Hardware Stress: Increasing the squeeze’s compressive force too intensely can potentially lead to damage to the mating hardware, depending on materials. This is especially important for high-repetition seal applications.
Friction and Wear: The higher the squeeze, the faster a seal will wear out. More squeeze inevitably creates more friction which can have a direct impact on how well the equipment in question performs. O-ring damage caused by pinching can also be a side effect of too much friction, leading to a loss of seal effectiveness over time.
Compression Set: The force exerted by the squeezed elastomer will gradually lessen over time. Once the O-ring retains its squeezed shape even without being squeezed, it is susceptible to losing its ability to seal properly. The term “compression set” is a measure of this occurrence; by the time an O-ring reaches 80% compression set, it’s likely less effective at sealing. Higher squeeze levels typically take longer to reach this 80% threshold.
Material: An O-ring’s material drastically impacts its relationship with squeeze. Nitrile rubber, for example, can reach far higher squeeze levels than Perfluorinated elastomers, which may rupture when squeezed too hard.
All seals are not created equal. The ideal component for one application may fail over time when integrated into a similar, but slightly different process. It’s critical to work with a seal supplier who thoroughly understands how seals will ultimately perform with different mating hardware, under different temperature conditions, and within unique situational parameters.
Wyatt Seal is that partner.
We’re experts in seal technology for a wide variety of industries. Our clients range from oil and gas to industrial to manufacturing and more. Let our friendly technicians provide you guidance on exactly which seal makes the most sense for your application.