A standard rotary shaft oil seal is generally designed to retain lubricant under conditions close to atmospheric pressure on its air side. It should not automatically be used in a pressurized housing.
This is an important distinction when selecting seals for pumps, gearboxes, hydraulic equipment, and other rotating machinery. A seal that performs well in a conventional gearbox may not be suitable when the housing is exposed to additional internal pressure.
Why Does Pressure Change the Sealing Requirements?
A conventional rotary shaft seal uses a flexible sealing lip that maintains contact with the rotating shaft.
When pressure builds up on the fluid side, it acts on the lip and changes the forces within the sealing structure. Depending on the design, excessive pressure can deform the lip, increase contact loading, generate additional heat, and accelerate wear.
In some cases, the lip may lose its intended geometry or become unstable during operation.
The result can be leakage, premature wear, or damage to the seal.
Why a Standard Oil Seal Is Not a Universal Pressure Seal
The pressure capability of a rotary shaft seal depends on its profile, lip support, material, shaft speed, temperature, and lubrication.
Some specially designed rotary shaft seals can operate under defined pressure
conditions. These may use reinforced structures, modified lip geometry, or other
design features to handle the additional load.
However, a pressure-capable seal must be selected according to its manufacturer's specifications. A standard TC or other conventional profile should not be assumed to have the same capability.
Conventional rotary shaft lip seals as normally operating with atmospheric pressure on the air side and only a limited pressure difference. Applications outside the specified conditions require consultation with the seal manufacturer.
What Should Be Checked Before Selection?
If the equipment operates under pressure, provide the seal supplier with more than the shaft and housing dimensions.
Important information includes:
Maximum and normal operating pressure.
Whether pressure is continuous, intermittent, or fluctuating.
Shaft diameter and rotational speed.
Operating temperature and lubricant.
Available installation space and housing design.
Also determine whether the equipment can use a pressure-balancing arrangement or a separate pressure-rated sealing system.
For some applications, a dedicated pressure-rated rotary seal or a different sealing arrangement may be more appropriate than a conventional oil seal.
The key is to select the seal according to the pressure it must actually withstand. Similar dimensions do not mean similar pressure capabilities.
