A scuba diving regulator first stage is the part of the regulator that accomplishes the first stage of pressure reduction, reducing the high-pressure tank air to an intermediate pressure. An open-water-style regulator first stage usually connects to four hoses, three that transport intermediate-pressure air to second stages and the buoyancy compensator's (BC) inflator, and one that allows high-pressure air to flow directly from the tank to the submersible pressure gauge.
1. First Stage Body
This metal cylinder contains the mechanisms that reduce the high pressure air in the scuba tank to an intermediate pressure. High pressure air flows in one side of the first stage body, undergoes pressure reduction, and then flows out through the low pressure hoses.
2. Yoke
The regulator first stage body is held against the scuba tank's valve through one of two methods: a yoke or a DIN fitting.Learn more about the difference between DIN and yoke regulators. This diagram illustrates a yoke fitting, also called an international fitting. The “yoke” is the metal oval that fits over the tank valve to hold the regulator in place.
3. Yoke Screw
The regulator's yoke is equipped with a yoke screw, a metal screw that runs through the regulator yoke and tightens the regulator first stage body onto the tank. To tighten the yoke screw, the diver turns the black, plastic handle attached to the screw.
4. Dust Cap
It is extremely important that no water enters the regulator first stage body. When the first stage body is tightened onto a tank, it creates a water-tight seal to the tank valve. However, when the first stage body is disconnected from the tank, it is possible that water could enter the opening in the first stage through which air passes from the tank to the regulator. The dust cap is a rubber cap that can be placed over the regulator first stage opening and tightened down using the regulator yoke screw. This seals closed the opening on the first stage.
5. Port/ Port Plug
Regulator first stage bodies have multiple openings, or ports, that regulator hoses can be screwed into. Usually, regulators have more ports than the standard number of hoses, which allows divers to position their hoses in a variety of configurations. These openings are called ports, and the plugs that close the regulator ports when they are not in use are called port plugs.
