7-2
U.S. Navy Diving Manual—Volume 2
7-2.1
Equipment Authorized for Navy Use. Only diving equipment that has been certi-
fied or authorized for use by the NAVSEA/00C ANU list shall be used in a Navy
dive. However, many items, such as hand tools, which are not specifically listed in
the ANU list or do not fit under the scope of certification and are deemed valuable
to the success of the dive, can be used. A current copy must be maintained by all
diving activities. The ANU list can be found on the Internet at http://
www.navsea.navy.mil/sea00c/doc/anu_disc.html.
7-2.2
Open-Circuit Scuba. All open-circuit scuba authorized for Navy use employ a
demand system that supplies air each time the diver inhales. The basic open-circuit
scuba components are:
Demand regulator assembly
One or more air cylinders
Cylinder valve and manifold assembly
Backpack or harness
7-2.2.1
Demand Regulator Assembly. The demand regulator assembly is the central
component of the open-circuit system. The regulator delivers air to the diver after
reducing the high-pressure air in the cylinder to a pressure that can be used by the
diver. There are two stages in a typical system (Figure 7-1).
7-2.2.1.1
First Stage. In the regulator’s first stage, high-pressure air from the cylinder
passes through a regulator that reduces the pressure of the air to a predetermined
level over ambient pressure. Refer to the regulator technical manual for the
specific setting.
7-2.2.1.2
Second Stage. In the second stage of a regulator, a movable diaphragm is linked
by a lever to the low-pressure valve, which leads to a low-pressure chamber.
When the air pressure in the low-pressure chamber equals the ambient water pres-
sure, the diaphragm is in the center position and the low-pressure valve is closed.
When the diver inhales, the pressure in the low-pressure chamber is reduced,
causing the diaphragm to be pushed inward by the higher ambient water pressure.
The diaphragm actuates the low-pressure valve which opens, permitting air to
flow to the diver. The greater the demand, the wider the low-pressure valve is
opened, thus allowing more air flow to the diver. When the diver stops inhaling,
the pressure on either side of the diaphragm is again balanced and the low-pres-
sure valve closes. As the diver exhales, the exhausted air passes through at least
one check valve and vents to the water.
7-2.2.1.3
Single Hose Regulators. In the single-hose, two-stage demand regulator the first
stage is mounted on the cylinder valve assembly. The second-stage assembly
includes the mouthpiece and a valve to exhaust exhaled air directly into the water.
The two stages are connected by a length of low-pressure hose, which passes over
the diver’s right shoulder. The second stage has a purge button, which when acti-
vated allows low-pressure air to flow through the regulator and the mouthpiece,
forcing out any water which may have entered the system. The principal disadvan-
tages of the single-hose unit are an increased tendency to freeze up in very cold
water and the exhaust of air in front of the diver’s mask. While the Navy PMS
