Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 119 / 881

12. With the heater in operation, check the pressure gauge. The gauge should read from 6.5 to 7.5 psi, if the
heater is running and the pressure indicated is more or less than required, adjust the regulator accordingly.
If the required pressure cannot be reached after a couple turns of the regulator's adjustment screw,
troubleshoot the fuel pump.
13. Place the heater switch in the “FAN” position. The heater should turn off and the ventilation blower
should continue to operate. Allow this blower to operate for a full two minutes, then place the air intake
lever in the closed position. The blower should turn off.
— Note —
This procedure should be followed after every shutdown to cool off the burn chamber.
14. With the air intake closed, turn on the heater switch, the heater should not ignite and neither fan should
operate. Turn off the heater switch and master switch.
15. Remove the pressure gauge and “T” fitting from the regulator.
DESCRIPTION OF HEATER AND BASIC COMPONENTS.
SPARK-SPRAY IGNITION. (Refer to Figure 21-3.)
The controlled atomized spray from a specially designed spray nozzle, coupled with high voltage spark plug
ignition, insures instant firing and continuous burning under all flight conditions.
Heat is produced by burning a fuel-air mixture in the combustion chamber of the heater. Aviation gasoline is
injected into the combustion chamber through the spray nozzle. The resulting cone-shaped fuel spray mixes with
combustion air and is ignited by a spark from the spark plug. Electric current for ignition is supplied by an
ignition unit which converts 14 volts to high voltage oscillating current to provide a continuous spark across the
spark plug gap. A shielded, high voltage lead connects the ignition assembly to the spark plug. Combustion air
enters the combustion chamber tangent to its surface and imparts a whirling or spinning action to the air. This
produces a whirling flame that is stable and sustains combustion under the most adverse conditions, because it is
circulated about itself many times. Therefore, ignition is continuous and the combustion process is self-piloting.
The burning gases travel the length of the combustion tube, flow around the inside of the inner tube, pass through
crossover passages into an outer radiating area, then travel the length of this surface and out the exhaust.
Ventilating air passes through the heater between the jacket and combustion tube assembly outer surface and
through an inner passage in the assembly. Consequently, ventilating air comes into contact with two or more
heated cylindrical surfaces.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2 1 - 4 2 - 1 0
Page 21-08
Revised: May 15, 1989
1E23
PIPER AIRCRAFT