Tips for Selecting the O-Ring Squeeze Ratio

May 07, 2018 FDA O-Rings

O-rings are the type of seals used in various process industries to prevent the leakage of gases or liquids. There are various factors that equipment designers need to consider while installing the O-ring seals. Squeeze ratio is one such factor that demands utmost importance when working with O-ring seals. What is the squeeze ratio? Why does it matter? Read this post to know more.

An Introduction to the Squeeze Ratio

The squeeze is a ratio of the applied deformation on the seal. It is the percentage of the cross-sectional thickness of the seal in the free state. In short, the squeeze is a measure of the deformation undergone by the seal when it touches the mating hardware. The O-rings are the type of seals that have a certain elasticity. This elasticity resulting from the hardware and seal contact helps block the flow of gases, liquids, or other fluids.

The higher squeeze will result in higher forces against the hardware. This, in turn, leads to a tighter sealing. However, it is not necessary that the designers always specify the greater squeeze to ensure a proper sealing. There are several other factors that they need to consider for a greater squeeze.

How to select Perfect

Factors to Consider While Deciding the Right O-Ring Squeeze Ratio

The following are the factors that will aid in the deciding the right squeeze ratio:

Compression Set: The force exerted by the squeezed sealing material weakens gradually. At a certain point, the O-ring will retain its squeezed shape without actually being squeezed. This is when it loses it sealing capabilities. This is where “compression set” comes into the play. This term is used to refer the value when O-ring reaches 80% of its compression set. In short, it is the value where the O-ring becomes incapable of offering an effective sealing. The O-rings with high squeeze levels take a long time to reach to this compression set.
Stress on the Mating Hardware: As discussed before, increasing the compressive force of the squeeze will result in better sealing performance, still it is not recommended. Why? Increased compressive force can cause irreversible damage to the mating hardware, especially in the high-repetition sealing applications. Hence, it is important to check the stress on the mating hardware, before deciding on the compressive force.
Material of Construction: The material used to design O-ring also plays a key role in the squeeze ratio. For example, nitrile rubber used to build an O-ring can endure high squeeze levels when compared to various other fluorinated elastomers. Many elastomers may rupture abruptly at high squeeze ratios.
Friction and Wear: The higher squeeze may also lead to wear and tear. This is because the higher squeeze generates high friction.

O-rings mostly undergo damage due to pinching. What is it? Several times it is seen that pathways are created around the O-ring, if the squeeze is higher. Sealed fluid or gases may escape through these pathways. The pinching can be a side effect of friction, and it will affect the effectiveness of the sealing.

In addition to the above-mentioned factors, the designers also need to consider other factors such as pressure and temperature of the sealed materials before applying the squeeze. The correct squeeze ratio will help ensure effective O-ring sealing, as well as its long service life. If you are unable to make a decision on the correct squeeze ratio, it is always better to approach an industry expert. SSP Manufacturing, Inc. has helped several of its clients maximize the ROI on O-ring seals with its extensive knowledge of ideal O-ring squeeze ratios.