What does the tightness specification “watertight” mean?

The term “watertight” means that no water may pass through a component or connection under specified conditions. However, the term alone does not constitute a fully defined technical tightness requirement.

For an unambiguous assessment, at least the following conditions must be specified:

• the test medium,
• the test pressure or pressure difference,
• the test duration,
• the temperature,
• the test method,
• the maximum permissible leak rate.

A tightness requirement may, for example, be expressed as a maximum leak rate in mbar·L/s. However, this value alone does not demonstrate that a component is watertight under all operating conditions.

A component may be tight against water while gases or lower-viscosity liquids can still pass through very small leaks. Likewise, the result of a test performed with air cannot automatically be transferred to the behavior of the component when exposed to water or other liquids.

The permissible leak rate must therefore always be defined for the specific component, test medium, and application.

The selected test method must also be suitable for the required detection limit. Very low leak rates cannot always be verified reliably and reproducibly using conventional airborne ultrasonic equipment under normal industrial conditions.