Schrader valve

[1] A bicycle tire valve similar to the type found on automobile tires.
See also Presta valve.
[2] A spring loaded valve, similar to a tire valve, located inside the service valve fitting to hold refrigerant in the system. Special adapters with built-in depressors must be used to attach service hoses to Schrader valves.
[3] Spring-loaded device which permits fluid flow in one direction when a center pin is depressed and in other direction when a pressure difference exists.