Constant-flow Scuba Regulators
Constant-flow regulators start with a constant flow of gas and follow with a simple switch valve. They are commonly used in rebreathers, a type of tank that reuses exhaled gas.
They are the earliest type of breathing set regulator. They offer less control over gas pressure than other regulators, with most types limited to an on-off valve. They are the earliest and most traditional type of regulator.
Twin-hose Scuba Regulators
Twin-hose regulators are used with A-clamps and large circular valves, usually installed on top of the scuba tank. They usually employ a demand valve, which automatically detects inhales and supplies air accordingly. They consist of a pair of corrugated breathing tubes, one used for inhaling and the other for exhaling.
The exhale tube keeps the air inside to be returned to the regulator, where it is released through a second one-way valve. They usually include a stopping mechanism to keep the exhaled air from returning through the inhale tube. Some of them are home-made, constructed from butane regulators with spring-loaded diaphragms.
Two stage, single hose scuba regulators
These regulators make use of a first stage, which releases the gas from the cylinder, and a second stage valve that uses a variety of valve styles. They use a high-pressure port where the hose connects to the pressure gauge, as well as other minor ports for low-pressure hoses to deliver gas to other parts of the tank.
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