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2. Specify the operating conditions for the seal
Although this stage is sometimes difficult and time consuming it must be completed thoroughly if an appropriate unit is to be identified. You must understand the system in which the seal will operate so that the seal you select is consistent with the rest of the system.

The primary criterion for selecting a type of seal is the relative motion between the surfaces to be sealed: three cases are distinguished - static seals, shaft seals and seals for reciprocating motion. Secondary considerations that affect the type and material of the seal should then be considered:

  1. Environment in which the seal must operate
  2. Consequences of failure
  3. Commercial factors
  4. Operation and maintenance
The temptation for the design engineer to consider only functionality should be resisted: the time and effort expended at this stage is often rewarded when an optimum seal is selected.