The Stop Blocks are interlocked with the lockbell system, and therefore the conveyance has to be positioned on the bank or underground stations to operate the Stop Bocks. The onsetter / banksman will only be able to operate the Stop Block system once the onsetter's / banksman's key is placed and turned on in the lockbell system. 
 
A push button on the Deebar Interlocking Panel will activate the pneumatic solenoid switch which in turn will activate the direction control valve for up or down movement of the stop blocks.