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Chapter 5 — 10
Fig. 5.12
A basic scuba set, without harness, console, octopus reg. or buoyancy compensator
The
air hose
is a small diameter flexible tube made of pressure resistant material which carries air
from the first stage regulator to a
second stage regulator
(or
demand valve
) which in turn supplies
air to the diver through the mouthpiece. With inhalation, a diaphragm moves to open a valve in the
demand regulator, and air passes from the air hose to the diver, at the environmental pressure.
The diver exhales directly into the water through one or more one-way valves which should prevent
water from entering the demand valve during inhalation.
It is important that the pressure of the air supply to a diver does not vary as the scuba cylinder
empties, otherwise it will become progressively more difficult to breath as the tank pressure falls.
Modern first stage regulators are much improved on the earlier models and have incorporated
devices such as "balanced" valves to reduce this problem to some degree.
1.
Air supply, cylinder, tank
2.
On/Off cylinder valve
3.
First stage regulator
4.
Second stage regulator,
demand valve
5.
Pressure gauge, replaceable
by
Console with multiple gauges