Downward movement of the pressure plate moves down a pressure plunger, which in turn levers up the striker retaining lever, releasing the spring-loaded striker and allowing it to impact the stab sensitive detonator, triggering the main charge.
The downward motion of the pressure plate initiates a sequence of events leading to the release of the striker, which then strikes the detonator, triggering the main charge. This process is similar to other mechanisms that involve a falling object striking an activator.