b. Regulator Valve. The regulator valve, mounted
M.2, or M.3 fuel oil or JP-4 fuel as a combustible. The
electrical requirement is 24 volts-direct current (dc).
in the control head, consists of two parts-one is a
Refer to figure 71.5 for specifications.
solenoid-operated shut-off valve and the other is a high-
low pressure regulator which varies the pressure of the
150. Liquid and Air Systems
fuel being supplied to the nozzle assembly for high- or
a. Liquid Flow System. The liquid flow system
operates in conjunction with the combustion air flow
c. Nozzle Assembly. The nozzle assembly is
system to transfer the heat of combustion from the
contained in a tee, which is connected to the regulator
burner to the liquid to be heated. The combustion
valve outlet port by an elbow. The nozzle is a thin plate
chamber provides passages through which the liquid
orifice through which fuel is metered to the burner, and
flows. The combustion air is circulated around these
works with the regulator valve to assure a constant,
passages so that the chamber functions as a heat
smooth metered flow of fuel regardless of the fuel used.
exchanger. The liquid is forced into the inlet port at the
The burner is of the modified
side of the combustion chamber by an externally
vaporizing-pot type with a porous ceramic burner wick
mounted liquid pump. It leaves the heater through the
mounted in its base. Fuel enters the burner through the
fitting at the top of the combustion chamber. The liquid
fuel inlet connection, saturates the wick, and combustion
pump is powered by the electrical circuit of the heater.
occurs in the burner throat and the combustion
b. Combustion Air System. The combustion air
system provides the air to maintain combustion. The air
system consists of a blower motor fan and the
152. Electrical System
necessary air passages. The air enters the heater
through the larger opening in the heater base, passes
through the combustion air blower shell and into the
The heater electrical system controls the operations
burner. The air mixes with the fuel vapor in the burner
of the fuel, liquid, and air systems throughout the
and combustion occurs.
The hot, contaminated
complete heater cycle. It also provides safeguards
combustion air passes through ports at the far end of the
against electrical and mechanical failures. The remotely
combustion chamber, into the secondary heat
mounted control box assembly controls the circuits from
exchanger. During this time, much of its heat is
the power source to the heater and the fuel pump
transferred to the liquid. The air leaves the heater
through a connecting cable assembly.
through the centrally located exhaust opening.
a. Control Box Assembly.
(1) The control box assembly contains a circuit
151. Fuel Systems
breaker, control switch, and indicator lamp.
(2) The circuit breaker protects the system if an
electrical failure occurs. Located in the
power circuit to the system, the circuit
The heater fuel system provides a constant flow
breaker can disconnect the system entirely
of liquid fuel to the burner for combustion, and operates
when the reset button is pulled out. Never
in conjunction with the heater electrical system. Fuel is
pull the reset button, however, while the
supplied through a fuel pump and filter to the heater,
heater is in operation, since this will
and reaches the combustion chamber through the
eliminate the heater purging cycle.
regulator valve and nozzle.
(3) The control switch is a double-pole, double-
a. Fuel Pump. The fuel pump is electrically
throw switch with "ON-HI, OFF, ON-LO"
connected to the heater operating circuits and supplies
positions. The heater starts operating when
fuel at low pressure to the regulator valve. The pump is
the thermostat calls for heat after the switch
self-priming, requiring no bleeding or adjustment on first