Power Failure Mode
In the event of a power failure, the integrity of the key sequence must be maintained during manual operation of the valve. This is achieved simply by locking the ‘SLU’ Unit in the ‘OFF’ position thereby releasing the ‘C’ Key. (Even if power is restored, with the ‘C’ Key free, the valve/actuator will remain disabled).
The ‘C’ Key is inserted into the freewheeling ‘HWL’ handwheel assembly – this lock functions on a ‘declutching’ principle. With the ‘C’ Key trapped, the ‘HWL’ drive mechanism may be engaged thereby enabling the valve to be operated.
While the ‘C’ Key can be removed from the ‘HWL’ assembly at any time, it has to be exchanged through the ‘AKE’ unit to secure the continuation key (i.e. the ‘A’ or ‘D’ Keys in the above examples)- these keys will only release provided the valve has completed its full stroke.