How Scuba Diving Regulators Work
The scuba diving regulator is the most vital equipment in your underwater life support system. It has two functions: to reduce high pressure gas—which can be air or a derivative of air— to a lower pressure gas that is breathable underwater; and to provide you sufficient air flow you need at any depth underneath the sea. It is sometimes referred to as the demand valve but the demand valve is actually just a part of a scuba diving regulator.
Parts of the Scuba Diving Regulator
A diving regulator is composed of valves that control the amount and reduces the pressure of the gas coming out of the cylinder. The demand valve is the valve that carries gas to the mouth.
The regulator also has an A-clamp or DIN fitting, which is connected to the cylinder or gas tank; and a high pressure hose connected to a pressure gauge, which is used to check the pressure and the amount of gas remaining in the cylinder.
First Stage Regulator
Gas in the cylinder is fully compressed. Its pressure is about 200 times higher than the normal air pressure at sea level. This must be regulated so that you can use it underwater. In order for the regulator to do this and supply enough air flow, it must have two stages.
The first stage of the regulator, which can either be piston-type or diaphragm-type, is attached to the high-pressure gas cylinder. It allows the release of gas from the cylinder at an even rate. The gas taken out of the cylinder is always between 8-10 BAR higher than the ambient pressure regardless of the falling pressure inside the cylinder (pressure continues to go down as the gas is consumed), the depth, and the air flow rate. A mechanism of spring, the piston or the diaphragm and the control valve works to regulate this pressure.
Second Stage Regulator
A flexible tube connects the first stage of the regulator to the second or last stage, which detects and delivers your gas or air needs. Unlike the first stage regulator, the last stage of the regulator is always diaphragm-based.
The demand valve is part of the second stage of your scuba diving regulator and is also designed to detect if you have already started breathing in low pressure air. It is activated by a lever attached to the diaphragm. As you inhale, the pressure in the outer chamber falls and this prompts the diaphragm to move the lever to open the valve and allow more air to pass through it. As you exhale, the valve automatically closes.