Juergensen Marine
Mark 15 - Mod "O" Closed Circuit Mixed Gas Rebreather
Maintenance Manual
By
Kevin W. Juergensen
NOTE: This manual is broken up into 7 Chapters. I've divided each one into its own page for brevity.
CHAPTER ONE - THE MARK 15
Mark 15 Maintenance and Operation
The Mark 15 Closed Circuit Mixed Gas Rebreather was built for the US Navy by a couple of companies, most notably Rexnord, Inc. and BioMarine Industries.
Essentially, the Mark 15 was used for EOD work in the Navy - that is, Explosive Ordinance Disposal. They wanted a device that was quiet, and emitted no bubbles. Later, they required a device that was non-magnetic - so they developed the Mark 15.5 and later, the Mark 16.
Chapter One : Description of Operation
The Mark 15 - Mod “0” is a closed-circuit, mixed gas rebreather which re-circulates the diver's respiratory gas. At each breath the exhaled carbon dioxide is removed. Oxygen is mixed with a diluent gas, to maintain a pre-selected absolute oxygen level, permitting operation at great depth.
Compressed air, Trimix or Heliox can be used as a diluent, depending on the depth of the dive, and the preferences of the diver.
A man generally consumes between 0.4 and 2.0 liters of oxygen per minute, depending on his activity level. Tests have shown that over an extended period of time, a working diver will consume an average of about 1.2 liters of O2 per minute. Therefore. for a six hour dive about 432 liters (or approx. 15 cubic feet) of oxygen is required to meet the respiratory needs of the average man.
The Mark 15 provides approximately 21 cubic feet of O2 at a charging pressure of 3000 psi. thereby providing adequate reserve for a six hour dive.
The Mark 15 controls the partial pressure of oxygen supplied to the diver to +/- 10% of the set point. This set point is selected during the calibration procedure and may vary from 0.5 to 1.3 atmospheres.
For most diving applications, an Oxygen partial pressure of approximately 1.2 is recommended.
Assuming appropriate decompression and support equipment is available, the unit can be used for up to 6 hours of diving, independent of depth. The record depth for diving a unit of this kind was set by a diver working out of a saturation lock-out bell at 1,800 feet.
Functional Description Of The Mark 15 (Refer to Schematic 1)
The diver exhales into his mouthpiece (1) and his exhaled breath passes though the exhalation hose (2) over a moisture trap (3) and then through a carbon dioxide absorbent bed (4) where the carbon dioxide is removed. The gas next passes over the oxygen sensor assembly (5) containing three sensors. The gas then passes into the diaphragm (6) and back to the diver via the inhalation hose (7).
The Primary Electronics (28) powered by the battery (8) and activated by the switch (27) computes the value of Oxygen in the breathing gas by averaging the limiting the output of the three sensors and then displays this value on the Primary Display (9).
Once every five seconds, the electronics compares the average sensor output with the set control point and, when required, opens a solenoid (10) in the oxygen supply line to admit a pulse of Oxygen to the system. This pulse of Oxygen flows from a small accumulator (11) which was pressurized via a flow control orifice (12) with gas at a regulated pressure of approximately 175 psi above ambient by the 1st Stage Regulator (16).
The Oxygen is stored in a spherical tank (13) fitted with a manual shut-off valve (14). In the event that the diver wishes to manually add Oxygen to the breathing gas, he can bypass the solenoid by depressing the Manual Add Valve (17). To allow the diver to monitor the supply pressure in his Oxygen tank, a gauge (18) is provided
In order to keep the diver's breathing gas mixture at a pressure which is equivalent to his depth, the pressure of the breathing gas is referenced to the water by the CounterLung (6). As the diver descends, the increased water pressure operates a Diluent Automatic Add Valve (19) maintaining the total pressure within the system at ambient water pressure. As the diver ascends, the water pressure lessens, and the Overpressure Relief Valve (20) is opened, permitting breathing gasses to vent to the surrounding water.
The Diluent gas is contained in a spherical tank (21) with a manual shut-off valve (22) and 1st Stage regulator (23). A Manual Add Valve (24) allows direct addition of Diluent to the breathing mix. A Pressure Gauge (25) is provided to indicate the tank pressure.
The Secondary Display (26) does not require battery power to operate. The power required to read each sensor is derived directly from the sensor itself. The display also indicates the automatic control system battery voltage (plus and minus).
Chapter Two - Various Models of Rebreathers
Chapter Three - General Maintenance of Systems
Chapter Five - Keeping it Working
Chapter Six - What to Look Out For - (Warning Signs)
Chapter Seven - Personal Philosophy of Handling Emergency Situations
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