Quantifying Water Vapor Diffusion across Elastomer Pressure Sensor Seals
Water vapor diffusion across elastomer seals causes reference cavity pressurization and dielectric drift, requiring coulometric ISO 15105-2 verification.
Squeeze Ratio
Compression Metric
A dimensional proportion expresses the percentage of deformation applied to an elastomeric seal when it is installed in its gland. Calculating the squeeze ratio involves comparing the original cross sectional thickness of the seal to its height after it has been compressed by the mating surfaces. This value determines the initial sealing force and the ability of the material to fill surface irregularities.
A proper balance is required to ensure a tight seal without causing mechanical damage to the elastomer.
Mechanical Integrity
Excessive compression can lead to permanent deformation known as compression set or cause the material to crack under thermal stress. When the squeeze ratio is too high, the friction during assembly increases and risks tearing the surface of the O ring. Conversely, a value that is too low will fail to maintain contact under low pressure or cold temperature conditions.
Engineers typically target a range between fifteen and thirty percent for static seals depending on the material hardness and the system pressure.
Tolerance Accumulation
The actual amount of compression in an assembly is influenced by the machining tolerances of the groove and the manufacturing variations of the seal itself. Designers must perform a worst case analysis to ensure the squeeze ratio remains within safe limits at both ends of the tolerance band.
Performance Validation
Field performance is verified through leak testing and visual inspection of the seals after they have been cycled under load. If the squeeze ratio is incorrect, the seal will show signs of extrusion or nibbling along the edges of the gland. Regular audits of the component dimensions ensure that the assembly process remains consistent with the original design specifications.