First Stage — What It Is and Why It Matters
The first stage is the component of a scuba regulator that attaches directly to the tank valve and reduces the high-pressure air in the tank (200 to 300 bar) to an intermediate pressure (typically 9 to 11 bar above ambient). It distributes this intermediate-pressure air through low-pressure ports to the second stage, octopus, BCD inflator, and drysuit inflator. It also has a high-pressure port for the SPG or wireless transmitter.
First stages come in two mechanical designs: diaphragm (sealed from the environment, better for cold and silty water) and piston (simpler, higher airflow, preferred for warm water). Environmentally sealed diaphragm first stages are the standard choice for cold-water diving where ice formation is a risk.
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Frequently Asked Questions
Should I choose a diaphragm or piston first stage?
Diaphragm first stages are preferred for cold water, dirty environments, and technical diving due to their environmental seal. Piston first stages are simpler and deliver slightly higher airflow but are more susceptible to freezing. For tropical warm-water diving, either works well.
What are high-pressure and low-pressure ports?
High-pressure (HP) ports connect to gauges or transmitters that need to read tank pressure. Low-pressure (LP) ports deliver intermediate-pressure air to your second stages, octopus, BCD inflator, and drysuit inflator. A typical first stage has 1 to 2 HP ports and 4 to 5 LP ports.
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