Sealing Shielding

O-Ring Squeeze - More is Not Always Better

O-Rings, Squeeze Values, Seals, O-Ring DivisionConventional wisdom says that the more an O-ring seal is squeezed (i.e. deformed relative to it’s “unsqueezed” state), the tighter the seal. More squeeze equals greater force between the O-ring and its mating hardware — which means that liquids, gases, and dry powders are otherwise prevented from flowing between the rubber seal and mating hardware.

An O-ring that’s being squeezed more also tends to maintain that force (and therefore the better seal) longer than an O-ring that’s being squeezed less. The failure of an elastomer to maintain its “push back” force over time is called the compression set. An elastomer with high compression set (generally more than 80 percent) no longer returns to its original uncompressed shape when it is not being squeezed. However, the assumption that increasing the squeeze on the O-ring will result in a better seal may not always be correct, depending on other factors. These include:

 

Installation damage

The more forcefully you squeeze O-rings during installation, the more likely you are to pinch them, creating pathways for leaks. That was the finding when Parker compared two finite element models used to predict the behavior of O-rings installed at 40 percent and 25 percent squeeze (Figures 1 and 2, respectively). At 40 percent, pinching of the O-ring between mating components was difficult to avoid, while at 25 percent installation pinching was virtually eliminated.

 

Mating hardware damage

As Figure 3 shows, the relationship is not linear between the amount of squeeze and the compressive load force required to maintain the squeeze. In fact, the compressive load force rises much faster beyond 30 percent squeeze. An O-ring requires almost two and a half times more load force to compress to 40 percent than it does to 25 percent. This level of compressive load could crush or deform lightweight or fragile mating components.

 

O-ring materials

The data presented in these figures are for 70 durometer nitrile rubber. Other materials, such as perfluorinated elastomers and compounds with low elongation (i.e., they only stretch  “so far”) may rupture when squeezed more than 30 percent. Other materials could experience accelerated compression set and reduced service life at 40 percent squeeze.

 

Application

While many variables affect an O-ring's form, fit and function, the most important parameter behind leak-free sealing is the amount of squeeze applied. Yet, as these data indicate, the ideal amount to squeeze is itself influenced by many factors. You can't just assume that more is better.

Keep in mind that other factors that can cause an O-ring seal to perform poorly, such as thermal degradation, chemical interactions, gas permeation, mechanical damage such as extrusion or wear, or low-temperature loss of resiliency. In these situations, adjusting the amount of squeeze is not likely to fix the problem.

Figure 1: At 40 percent squeeze, an O-ring is likely to be pinched during installation

Figure 1: At 40 percent squeeze, an O-ring is likely to be pinched during installation

Figure 2: Even with poor lubrication, installation with 25 percent squeeze shows little risk of damage

Figure 2: Even with poor lubrication, installation with 25 percent squeeze shows little risk of damage

Figure 3: Compressive load force increases substantially beyond 30 percent squeeze

Figure 3: Compressive load force increases substantially beyond 30 percent squeeze

This article was written by Dan Ewing, Engineering Supervisor at Parker's O-Ring Division in Lexington, Kentucky.

You can find more support info and FAQ's on our website at this Support Link. If you have an immediate question, we have live chat with our application engineers available for a number of our divisions - look for the "Chat with an Engineer Button."

 

More support content from the Sealing and Shielding team:

Get Rid of Stick-slip Trouble With These Tips

Selecting the Right O-Ring Seal Squeeze Ratio

Top 10 Most Popular O-Ring and Lathe Cut Blog Posts of All Time

Sealing Fundamentals | Face Seal

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Comments for O-Ring Squeeze - More is Not Always Better

Cindy Harbaugh
The more forcefully you squeeze O-rings during installation, the more likely you are to pinch them, creating pathways for leaks.
ovid balten
Interesting article on O-ring squeeze. Have a question re an existing design of an electronics enclosure where top cover is sealed to box with an O-Ring.
Typical operating environment is air, at times may get submerged 1 m. Thus:
- face seal
- gas
- 1/16" O-ring
Current design gland dimensions would generate a 41% squeeze.
The Parker recommended dimensions, Sect IV, Table 4.3 would generate a 32% squeeze.
Should we keep existing gland design with 41% compression or, change to PARKER recommended dimensions.
Dorothy Kern
Ovid, Thanks so much for reading the article and commenting.
For a .139" cross-section seal (~1/8" thickness), our general guidance is to target a designed squeeze of 20 to 30%. I tend to follow the column detailing the suggested squeeze percent, rather than the columns labeled "Gland Depth" and "Actual Squeeze". For a .139" cross-section, with the ±0.004" tolerance, the ideal groove depth will be .103±.003".

Dorothy Kern
Appl. Engineer Team Lead
Parker Hannifin, O-Ring & Engineered Seals Division

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