A review on the physiology of Insulin like Growth Factor-I (IGF-I) ... by Debnath, Surajit / Advances in Environmental Biology.
The spring piston airgun generates power using a powerful spring-loaded piston that is housed within a compression chamber. Cocking the gun (using a break barrel, side lever, or under lever mechanism) causes the piston assembly to compress the spring. When the spring is released it pushes the piston forward compressing a column of air in the chamber behind the pellet.
A return spring keeps the diaphragm in the starting position until the brake pedal is applied. When the brake pedal is applied, the movement pushes against a small spring which pushes against an air valve thus opening it to allow atmospheric pressure air to flow into the supply chamber of the booster.