TM 5-4520-208-15
fuel is bypassed at the pump or at the
the nozzle, forcing more fuel through
nozzle and returned to the fuel tank.
the nozzle orifice and raising the
The pump has three outlets. If the
temperature. As the temperature of
primary bypass line is closed by the
the discharge air reaches the selected
fuel control valve, fuel flows to the
heat, the heat sensing element of the
nozzle, and also through the second-
temperature selector valve will open
ary bypass line to the fuel tank.
the restriction and bypass more fuel.
When the fuel control valve is open,
Pressure drops at the nozzle and
the pump cannot build up sufficient
heat output settles to the setting
pressure to open the balanced pump
selected.
valve. There is always flow through
d. Heat Exchanger. Fuel flowing from the
the secondary bypass line as the fuel
nozzle is ignited in the combustor. The burn-
pump supplies fuel in excess of
ing fuel strikes a plate or target in the com-
nozzle capacity.
bustor and is diffused into the heat exchanger.
(4) Fuel control valve. Pushing the knob
Air from the fan enters holes in the side of
down closes the fuel control valve
the combustor in a manner that will ensure
proper fuel-air mixture. From the combustor,
The fuel control valve also acts as an
the burning fuel flows through the heat ex-
overheat valve. A heat sensing ele-
changer in a spiral path between the surfaces
ment is located in the heater dis-
of the ventilating air tubes and is expelled
charge air stream. When the air tem-
through the exhaust opening at the top of
perature exceeds 330F to 350F the
the casing. Ventilating or heating air is forced
fuel control valve will open, lower-
through the parallel tubes and the space be-
ing the pressure, and fuel will not
tween the heat exchanger shell and the casing.
flow to the nozzle.
Heat is exchanged between the hot exhaust
gases and the ventilating air. At the discharge
(5) Nozzle. The nozzle (fig. 35) is con-
end of the heat exchanger are the temperature
tained within the nozzle holder. On
sensing elements. The air control assembly
Model BT400-40 heaters the inlet
consists of a baffle, a series of radial tubes,
and bypass fuel lines are an integral
and an adjustable damper. Air traveling be-
part of the nozzle holder. Fuel
tween the' walls of the heat exchanger and
flows through the nozzle and is
the casing is directed radially inward behind
atomized. As the fuel leaves the
the baffle where it is mixed with warmer air
nozzle it is ignited by the igniter
leaving the parallel tubes of the heat exchang-
plug in the combustor. Fuel is also
er. This mixing insures a more uniform tem-
bypassed from the nozzle through
perature throughout the the discharge air
a check valve, to the temperature
stream. The shutter is controlled by a damper
selector valve on the control panel.
control which is locked by a handwheel
The check valve prevents a reverse
mounted in a slot above' the discharge end of
flow of fuel to the nozzle.
the heater. The damper is used to reduce the
(6) Temperature selector valve. The tem-
heat output, without reducing the air volume.
perature selector valve (fig. 11) al-
Volume can be set between full and one-half
lows the operator to select the tem-
of full volume. A duct adapter assembly is
perature of the discharge air. When
installed on the discharge end of the heater
the knob is turned, a pinion gear
to connect the flexible air hose as shown in
turns the temperature indicator knob.
The indicator knob pointer indicates
e. Cabinet. The power unit end of the
the discharge air temperature selected,
heater is inclosed in a cabinet (fig. 1) which
from 150F to 280F. Fuel flowing
affords protection against the elements and
through the temperature selector valve
prevents damaged during storage or transit.
is restricted to raise the pressure at
5