First stage valve:

The first stage has a high-pressure "port" for the high-pressure hose to the pressure gauge. It has a number of "ports" for low-pressure hoses to carry gas to other components, which serve as second-stage valves of various sorts. All unused ports must be blanked off.

With regulators that are used as breathing sources, at least one low-pressure hose connects to a demand valve. Some low-pressure hoses connect to the diving suit inflation valve and the buoyancy compensator inflation valves: these low-pressure hoses are called direct feeds.