Fail-open and fail-closed valves: What they mean and which is the safe position

The term fail position describes the position to which a valve is driven when motion energy or the control signal is lost.

Fail-closed

The valve closes upon loss of energy. In many fuel applications, this is the preferred safe position.

Fail-open

The valve opens upon loss of energy. It is used only where risk analysis and the process require this behavior.

Spring return

Many valves use a spring to automatically return to the safe position.

Correct interpretation

One should not assume that all gas valves have the same fail position. Always check the datasheet and the P&ID of the installation.