Just read Dieselboy's comment and wholly agree with his comments. Normally the flapper is spring loaded against the notch on the shaft. When activated- either by the solenoid or by a pull cable the pawl is pulled out of the notch and the flapper instantly closed. No air -engine stops. The pawl must be manually reset to open the flapper. This not difficult and should be easy to visualize once you take a look at the end of the shaft the flapper rotates on.