The control valve is a metal part fitted over the top of the scuba tank. Divers attach the first stage of their regulator to the tank's control valve. The control valve passes air into the diver's regulator, allowing the diver to breathe under water.
Air Flow
The tank's control valve has a twistable knob attached to the side of it. This knob controls the piston inside the valve and allows you to open or close the tank's flow of air. If you open the valve to allow air to flow out of the tank before attaching the regulator, you will be surprised by the loud sound of air rushing out of the tank. Once you attach the regulator to the valve, you can safely turn the knob to open the valve without losing the tank's air. Modern regulators only supply air when the diver inhales.
O-Ring Seal
K-valves, yoke valves and DIN valves all contain O-rings. These small, soft rings allow an air-tight seal to form between the metal of the tank's valve and the metal of the regulator. On yoke valve tanks, the regulator fits over the valve and O-ring and attaches with a screw or knob.
Y-Pillar Valve
Y-pillar valves work like k-valves or yoke valves, but they have two outputs and valves instead of one. Y-pillar valves allow divers to attach two regulators to one tank.
Air Pressure Control
Most tanks can carry air at a pressure up to 3,500 pounds per square inch. The regulator's first stage reduces the tank's air pressure to an intermediate pressure of about 150 psi, according to scuba-diving-smiles.com. The regulator's first stage, or mouthpiece, further reduces the pressure of the air to match the surrounding water pressure.
Regulator Airflow Control
The regulator's first and second stages contain pistons just like the tank's valve. When the diver inhales, he lowers the pressure in the regulator's compression chambers and causes the pistons to move to the open position. When the diver exhales, the pistons return to the closed position to prevent air from continuing to flow.
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