Instructor Manual
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Ocean Diver
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Adapting to the underwater world
Copyright © BSAC 2017
16
Regulator
Delivers breathing gas
The gas in a diving cylinder is at high pressure, anything
up to 300 bar. It would be impossible to breathe directly
from the cylinder so the regulator has been designed to
reduce the pressure of the gas leaving the cylinder and deliver it to the diver at
ambient pressure so that it is easy to breathe whenever the diver wants to. The
regulator is also referred to as a demand valve, or DV, for this reason.
Features
• First and second stages
The regulator first stage fits to the cylinder valve with either with an A-clamp or
DIN fitting (5/8” BSP or possibly M26).
When the cylinder valve is opened the first stage reduces the pressure in the
cylinder to an intermediate pressure around 10 bar above the local absolute (or
ambient as it is also known) pressure.
The gas at this inter-stage pressure is passed down an intermediate pressure
hose to the regulator second stage.
The second stage further reduces the gas pressure from inter-stage pressure to
equal ambient pressure and delivers gas to the diver when they breathe in.
When the diver breathes out the exhalation is expelled via the exhaust valve
into the water.
If water enters the second stage it can be easily cleared by either breathing out
or by pressing the purge button located on the front face of the regulator.
The fail-safe design of regulators usually means that they will ‘free-flow’,
continuously delivering gas if a mechanical fault occurs. Training includes how
to breathe from a free-flowing second stage.
• Hoses
As well as the inter-stage, intermediate pressure hose, a regulator set will
probably have further intermediate pressure hoses for connection to a buoyancy
compensator direct feed and a dry suit direct feed.
• Alternative supply
The alternative supply is an additional second-stage regulator connected to the
first stage via its own intermediate pressure hose to provide a backup system.
This additional second stage is commonly known as an octopus rig and, as a
backup system should be easily identifiable. Yellow marked hoses and second
