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.
Pump - A device which converts mechanical force into hydraulic fluid power. Basic design types are gear, vane, and piston units. Fixed Displacement Pump - A pump in which the output per cycle cannot be varied. Variable Displacement Pump - A pump in which the output per cycle can be varied.