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S
ince divers don’t have gills, we have to carry our
own air supplies with us if we want to spend any
time underwater. For the average recreational scuba
diver this means strapping on a tank of compressed
air. However, human bodies are not designed to breathe
compressed air, so we need a way to transform it into
something our lungs can comfortably handle. That’s the job
of a scuba regulator.
SCUBA REG SMACKDOWN
In one corner there’s the scuba tank, filled with compressed
air or nitrox. This high-pressure (HP) air can range from
2,250 pounds per square inch (psi) in older steel 72 tanks
to 3,000 psi in a typical aluminum 80, to around 3,500 psi
in modern high-pressure steel tanks. Recreational divers in
Europe may use even higher-pressure tanks.
In the other corner there’s the diver who needs air at
ambient pressure to breathe. On the surface, ambient
pressure is 14.7 psi; at 66 feet deep it is about 44 psi
(3 atmospheres at 14.7 psi per atmosphere).
In between tank and diver, there’s the scuba regulator. A
regulator can be broken down into three basic components:
1. the first stage that attaches to the scuba tank
2. the second stage the diver holds with his mouth
3. the interstage hose that connects them together
The job of the first stage is to take the HP air in the tank
and step it down to what’s called intermediate pressure (IP),
which, depending on the regulator, normally ranges from
125 to 145 psi more than ambient pressure.
When a regulator is connected to a tank and the tank
valve is opened, HP air flows into the first stage’s HP
chamber. Next it flows into the IP chamber, where air
pressure is reduced. From there it travels through the hose
to the second stage, where IP air is stepped down to ambient
pressure before entering the diver’s lungs.
This step-down air-delivery process is triggered when — and
only when — the diver inhales. Because of this, scuba regulators
are referred to as “demand-type” air-delivery systems.
PISTON AND DIAPHRAGM FIRST STAGES
Separating the HP and IP chambers in the first stage is a
mechanism that controls the flow of air from one chamber
to the other. Depending on the regulator, this mechanism
will be either a piston or a diaphragm.
In a piston system, when a diver takes a breath from his
second stage, the pressure in the first stage IP chamber
drops. This causes a spring to expand, which draws the
piston off its seat and opens the channel between the HP
and IP chambers. Air then flows from the HP chamber into
the IP chamber, compressing the spring and returning the
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SPRING 2012
GEAR
Breathe In, Breathe Out
Demystifying the inner workings of the scuba regulator
B Y J O H N B R U M M
high-pressure
air from tank
ambient
water
pressure
valve and
high-pressure
seat
diaphragm
intermediate
chamber
main
spring
intermediate
pressure to
second stage
Diaphragm First Stage
high-
pressure
air from
tank
high-
pressure
air chamber
high-
pressure
seat
balanced
piston
assembly
intermediate
pressure
chamber
high-pressure
spring
intermediate
pressure to
second stage
Piston First Stage