17-2
U.S. Navy Diving Manual—Volume 4
17-2.1
Recirculation and Carbon Dioxide Removal. The diver’s breathing medium is
recirculated in a closed-circuit UBA to remove carbon dioxide and permit reuse of
the inert diluent and unused oxygen in the mixture. The basic recirculation system
consists of a closed loop that incorporates inhalation and exhalation hoses and
associated check valves, a mouthpiece or full face mask (FFM), a carbon dioxide
removal unit, and a diaphragm assembly.
17-2.1.1
Recirculating Gas. Recirculating gas is normally moved through the circuit by
the natural inhalation-exhalation action of the diver’s lungs. Because the lungs can
produce only small pressure differences, the entire circuit must be designed for
minimum flow restriction.
17-2.1.2
Full Face Mask. The FFM uses an integral oral-nasal mask or T-bit to reduce dead
space and the possibility of rebreathing carbon dioxide-rich gas. Similarly, check
valves used to ensure one-way flow of gas through the circuit must be close to the
diver’s mouth and nose to minimize dead space. All breathing hoses in the system
Figure 17-2. MK 16 MOD 0 UBA Functional Block Diagram.
TO CENTER
SECTION
DIAPHRAGM
ASSEMBLY
OXYGEN
ADDITION VALVE
DILUENT
BYPASS VALVE
DILUENT
INLINE FILTER
DILUENT HIGH
PRESSURE INDICATOR
DILUENT
BOTTLE VALVE
DILUENT
REGULATOR
DILUENT
BOTTLE
PRIMARY
BATTERY
PRIMARY
ELECTRONICS
OXYGEN
REGULATOR
OXYGEN
BOTTLE VALVE
OXYGEN
BOTTLE
OXYGEN HIGH
PRESSURE INDICATOR
OXYGEN
INLINE FILTER
OXYGEN
BYPASS VALVE
CHECK VALVE
DILUENT
ADDITION VALUE
DIAPHRAGM
DUMP VALVE
TO PRIMARY
DISPLAY
TO SECONDARY
DISPLAY
OXYGEN
SENSORS
INHALATION
HOSE
MOUTHPIECE
ASSEMBLY
EXHALATION
HOSE
ABSORBENT
CANISTER
