Piper Navajo Chieftain PA-31-350 Service Manual page 804

NAVAJO CHIEFTAIN SERVICE MANUAL
3.
Install plugs and caps in all openings except the one to which the combustion air pressure
switch is attached. (Any opening can be used to connect the air pressure source; however, the combustion
air pressure switch opening is usually the most convenient. The drain opening would normally be
considered a second choice.)
4.
Connect a regulated air supply to the opening that has not been plugged and apply a
pressure of between three and five psi to the combustion tube assembly.
5.
Submerge the combustion tube assembly in water for several minutes while watching for
bubbles. which would indicate leaks. No air leakage is permitted from the combustion tube assembly. No weld
or braze repairs are permitted on a combustion tube assembly.
c.
Test the combustion air pressure switch as follows. (Refer to Figure 13-15.)
1.
Connect an adjustable air pressure line that can be controlled in a range of zero to 5.0 inches
of water to the switch opening with a water manometer and needle valve in the line ahead of switch. Switch
must be tested in position as installed in the airplane.
2.
Connect an ohmmeter across the switch terminals to determine the exact instant of switch
closing.
3.
Apply air pressure allowing it to build up very slowly from zero. The switch contacts should
close at 0.5 + 0.1 inches of water which will be indicated on the manometer.
NOTE
The switch cover has a differential pressure tap and this opening
must be left open to atmosphere during the test.
4.
Make several trials to insure switch reliability. Be sure to increase and decrease the air
pressure slowly in order to produce accurate indications.
5.
If an adjustment is required, rotate the adjusting screw clockwise to increase settings and
counterclockwise to decrease settings.
d.
Test the fuel feed and nozzle holder assembly for leaks as follows: This test can be simplified if
the following routine is used to test both the fuel line and fuel line shroud tube.
1.
Using filtered compressed air, apply 20 psi to the shroud drain port located on the surface
near the threaded nozzle cavity.
2.
Immerse the fuel feed and nozzle holder assembly in clean water with the fuel inlet and
nozzle cavity left open.
3.
Observe for bubbles which would indicate leakage. If bubbles appear at either fuel fitting,
there is a leak in the fuel tube. If bubbles appear externally on the shroud tube, or at either end of the
shroud tube juncture. the shroud tube is leaking.
4.
In either of the above cases, the complete fuel feed and nozzle holder assembly must be
replaced.
e.
Spray test the nozzle (23) (Figure 13-17) as follows:
1.
Install the nozzle in the fuel feed and nozzle holder assembly. Connect the fuel tube to the
fuel solenoid. Connect solenoid to a 7 psi fuel pressure source.
2.
Connect the solenoid leads to a 24-volt battery. Connect a switch in the line to open and
close the solenoid when desired.
3.
With the switch closed (solenoid valve energized) and the fuel line connected, observe the
fuel spray pattern. It should be conical in shape with even dispersion in all directions.
Revised: 3/5/84
4C12
HEATING AND VENTILATING SYSTEM
4C 12