We just learned about the Gasket that helps keep a valve from leaking.
Another part of a valve is the Valve Spring.
Some valves use a spring to keep a valve closed, but if there is a lot of pressure they will squeeze and let the disc open and let some pressure out.
Once enough pressure is let out, the spring will push the disc closed again.
(from: wikipedia - relief valve)
Kid Facts - Blast from the past: Le Prieur Rocket
