Whenever valves are actuated by means of pneumatic, hydraulic or electrical power sources, Smith Flow Control (SFC) can supply key-exchange interlocks which can be easily integrated into the actuator operation. By allowing complete manual control of the actuators, the interlocks allow the actuated valves to be incorporated into a complete key-exchange interlock sequence with other critical process valves. Due to the high torque applied during valve actuation, mechanical locking is not practical, and interlocking of the actuator control mechanism is preferred. As there are often two or more ways of operating actuated valves, they all need to be accommodated within the interlocking system. SFC interlock systems for electrically-actuated valves have three main components: a switch panel interface interlock, a manual override interlock, and a valve position proving device. These ensure firstly that the actuator’s failsafe function is not compromised, secondly, that the valve “absolute position” (open and/or closed) is independent of any on-board instrument indication, and finally that the actuator manual override cannot be used to override the interlock function. In addition, on electrical actuators where the key interlock system de-energises the valve, any circuitry — for example anti-condensation heating circuitry – remains uninterrupted. A similar range of key interlock designs are also available for both spring-return and non-return hydraulic actuators and for spring-return pneumatic actuators.
