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In this thread on O2 control, I thought I
would outline the system that I am using on my boat. I am about a year and a half into the fabrication of a one-man,
one-atm. submersible rated to 300 ft. After much thought, and with the
intent to stay within ABS rules, the following is what I ended up using.
The normal mission time is 8 hours with provisions for additional 72
hours of emergency life support. Components:
1 each Scuba first stage regulator (Aqualung
Titan First Stage - Setup for 100% O2)
2 each Medical "E" size tank, 24 SCF, 2015
psig max
2 each Medical "D" size tank, 15 SCF, 2015
psig max
1 24VDC solenoid (O2 clean), NC, controlled
by PLC
1 each Barometric pressure transducer, 0-5 VDC
output , 700-1100 mbar
1 each Backup Oxygen Regulator 0-8 LPM H-Style
gauge, John Bunn # 106 JB0150-085
8 each Filter Cartridges, CO2 Scrubbing,
"4-8". mesh Sofnolime, 4.5 lbm/cartridge
1 each Flow-Control Needle Valve
1 24 VDC blower for circulation of cabin
air through the filter system
1 each CO2 Sensor, 0-2000 ppm
1 each Maxtec MAx-250 O2 sensor
element
Normal operation:
When the hatch is closed, the PLC records the
barometric pressure in the hull. When the barometric pressures drop 10
mbar below the last hatch closure pressure, PLC signals solenoid valve to open
in the regulated O2 supply. Four small external tanks for O2 are
manifolded and located inside a FRP cowling to minimize drag. The
first stage regulator is set to deliver 25 psi above ambient water
pressure. When barometric pressure has been restored to the hatch closure
pressure, the solenoid is closed. A needle valve down stream of the
solenoid valve is adjusted so that a the surface, it takes 60 seconds to
restore pressure to 1 atm. Cycle is repeated to maintain cabin
pressure at 1 atm. The 100% O2 is introduced at the inlet to the
scrubber. O2 and CO2 sensor measurements are displayed on a touch
screen display and are for information only, not control. PLC will issue
visual and audible alarms if O2 or CO2 levels go out of range.
Emergency operation:
In the event both the main power and backup power
fail, the operator can manually adjust a medical oxygen regulator with a
dial indicator from (0-8 lpm) . For one man, 0.5 lpm is
nominal rate.
All the elements of the life support system have
been installed in the boat and leak tested. SS Swaglelok fittings were
used for air and O2 gas lines. A scuba first stage regulator was used
for O2 so that in an emergency, I can blow MBT at depth with either air or O2 by
opening a crossover solenoid valve between the air and O2 systems from the touch
screen panel.
In the next several weeks, I will be doing some
life support tests in my shop so should be able to confirm how both the primary
and backup systems work. If the automated system proves to be problematic,
I will just use the backup system as the primary which is a fixed metered
flow rate of O2 into cabin and monitor the O2 and CO2 levels.
Cliff
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