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.
The spring brake contains an additional air diaphragm and a very strong spring. When air is applied to the spring brake, the spring is held in the off position by the air diaphragm. When the air is exhausted, the spring provides the braking force to the air chamber pushrod, thus actuating the brakes.