spring pressure or by backup power.

The modes of failure operation are requirements of the failure to safety process control specification of the plant. In the case of cooling water it may be to fail open, and the case of delivering a chemical it may be to fail closed.

Valve positioners

The fundamental function of a positioner is to deliver pressurized air to the valve actuator, such that the position of the valve stem or shaft corresponds to the set point from the control system. Positioners

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