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Seals

Seals prevent leakage of fluids (oil, water, gas) through gaps in fixed or moving machine parts and block ingress of foreign matter from outside. They are broadly divided into static seals for fixed parts, such as O-rings and gaskets, and dynamic seals for reciprocating or rotating shafts and rods, such as sliding seals and packings. An O-ring is fitted into a groove and compressed, and it seals through its restoring force. Resin sliding seals such as those made of PTFE offer low friction and chemical resistance, and some are combined with rubber energizers (elastic members that press the seal) to supplement sealing force. They are used in a wide range of applications, including hydraulic and pneumatic equipment, valves, vacuum systems and manufacturing equipment.

How to choose Seals

  1. 1. Select the inner diameter to suit the mating part and groove

    An O-ring must be selected with an inner diameter matched to the shaft diameter and groove dimensions it fits. Selecting by a nominal size compliant with standards such as JIS B 2401 makes it easier to align with groove design. Listed products cover inner diameters from 15 to 1055 mm, and there are application-specific series such as those for vacuum flanges.

  2. 2. Check cross-section diameter and squeeze

    The cross-section diameter (wire diameter) and groove depth determine whether an appropriate squeeze (compression amount) can be achieved. An incorrect fit causes leakage, extrusion or early deterioration. O-rings for vacuum flanges come in series such as 4 mm, 6 mm and 10 mm, so select by checking against the groove dimensions.

  3. 3. Select a material suited to the fluid and environment

    Material is selected based on resistance to the sealed fluid. Rubber materials differ greatly in oil resistance, weather resistance and chemical resistance depending on type, while resins such as PTFE offer excellent chemical resistance and low friction. For vacuum applications, low outgassing should also be considered. Verify against a fluid-to-material compatibility chart.

  4. 4. Confirm operation is within the service temperature range

    Seal materials harden and degrade at high temperatures and lose elasticity at low temperatures, reducing sealing performance. Confirm that the maximum and minimum operating temperatures fall within the service temperature range, and if the seal is continuously exposed to high temperatures, also check the continuous service temperature. Temperature ranges may differ by grade even within the same product.

  5. 5. Allow margin below the maximum pressure

    If the operating pressure exceeds the maximum pressure, the seal may extrude into the gap and fail. Check that pressure, including surge pressure (momentary pressure rise), stays within the maximum pressure. Listed products include an example with a maximum pressure of 1000 bar; at high pressures, consider gap control in the groove and the use of backup rings.

  6. 6. Judge sliding applications by the limit PV value

    For dynamic seals used in reciprocating or rotating motion, wear increases sharply when the PV value, the product of pressure and speed, exceeds the limit PV value. Listed products include examples with a limit PV value of 1.5 MPa·m/s and a maximum sliding speed of 0.5 m/s. Calculate from the operating pressure and speed, and confirm that both upper limits are met.

This guide was written by AI based on the listed products' documents and specification items. Check each manufacturer's documents before adopting.