Before you pull the trigger, the piston is at a position where its valve is blocking the passage between the lower gas passage and the connecting gas passage. The valve is supported by a small spring. You pull the trigger, and the hammer hits the head of the movable pin. The movable pin hits the head of the piston. The piston moves forward and the valve opens, therefore the gas can flow through the connecting gas passage to the upper gas passage.
Total Views: 800 ,
