Regulators
The regulator is to supply air to the scuba diver at ambient pressure. The first stage attaches to the tank and reduces the air pressure in the tank to ambient pressure plus to preset the intermediate pressure. The air is sent down a hose to the second stage. The pressure is then reduced by that same intermediate pressure, thus leaving air at ambient pressure.
First stages are balanced or unbalanced. Balanced first stages are designed for easy breathing at depths up to 90ft as when they are attached to the tank at the surface. Most regulators provide one or two high pressure ports for pressure gauges and three to four low pressure ports for the second stages, inflator hoses and dry suit hoses.
Second stages often offer external adjustments that can be made while diving to change the performance of the regulator.
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