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 thermostat is a temperature controlled valve. The spring loaded valve is attached to a small cylinder filled with thermal wax. As the engine warms up, coolant transfers heat to the wax-filled cylinder. The heat causes the cylinder to expand and pushes down on the spring loaded valve.