Spring Loaded Check Valve

spring loaded
A spring is an elastic object used to store mechanical energy. Springs are usually made out of hardened steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication.
Containing a compressed or stretched spring pressing one part against another
containing a compressed spring that presses one part against another
(Spring-loading) Options backdating is the practice of issuing options contracts on a later date than which the options have listed.

check valve
A mechanical device in a pipe that permits the flow of water or air in one direction only.
A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid (liquid or gas) to flow through it in only one direction.
A valve that closes to prevent backward flow of liquid
Limits the flow of gas to one direction only. Use a check valve between the bubbler and generator to prevent unwanted pressure build up in the generator, and a safety against a low level bubbler. A check valve, such as used on torches, is recommended.