We just learned about the Valve Stem that sticks up from the valve.
Another part of a valve is the Gasket.
This is a small circle that goes inside any place where two pieces of a valve have to be connected.
So at the top where the bonnet goes is sometimes a gasket, and then where the ports connect to other pipes is sometimes a gasket.
It's a way to help make sure that the liquid or gas doesn't leak out through where the two parts are connected.
Sometimes they're made out of rubber, but other times they're made out of paper or even metal.
(from: wikipedia - gasket)
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