Learning Event 3
DESCRIBE THE M2 WATER HEATER
The M2 water heater is used to heat water for equipment decontamination operations or personnel
showers. The M2 water heater is shown in Figure 11. It consists of three main components: the fuel and
ignition system, the combustion system, and the control system. The secondary components include:
removable panels, a control panel, a control box, a fuel hose assembly, an electrical power cable
assembly, a water hose assembly, a boiler assembly, a combustor assembly, two electrical motors, a
magneto, a filter, and tools.
FUEL AND IGNITION SYSTEM
The major operating components of the fuel and ignition system are installed on the M2 water heater
skid. A 24-volt DC fuel and ignition drive motor controls and drives the fuel pump and the combustor
ignition magneto. Fuel is supplied from an external source under constant pressure to the fuel pump
solenoid valve. The solenoid valve (Figure 11) controls fuel to the fuel pump. Some unused fuel is
bypassed at the fuel pump and is returned to the fuel supply. When the HEATER-ON/PURGE-ON
switch is in the PURGE-ON position (Figure 11), the fuel pump solenoid valve coil is not activated.
Fuel flows through the solenoid valve body and is returned to the fuel container. When the HEATER-
ON/PURGE-ON switch is in the HEATER-ON position (Figure 11), the coil of the fuel pump solenoid
valve is energized and closes the fuel passage in the solenoid valve body. The fuel is then redirected to
an atomizing fuel nozzle. The magneto supplies voltage to the igniter plug in the combustor, where the
fuel is ignited.
The major components of the combustion system are installed on the boiler. Water enters from the
bottom of the boiler (Figure 11) and is discharged from the top. The combustion exhaust gases are
discharged at the top of the M2 water heater. The system uses a forced air and atomized fuel mixture.
A combustion air fan (Figure 11) forces air into the combustor, where the air is mixed with the atomized
fuel spray. This mixture is then ignited by an igniter plug. The flame is self-sustained once it is lit.
The control system operates the fuel and ignition system and the combustion system. The controls, the
temperature gage, and the oil and water pressure gages are installed on the front of the control panel
(Figure 11). In addition, many automatic control and safety devices are installed throughout the M2
water heater to ensure safe and efficient use.