Piper Navajo PA-31 Service Manual page 944

FLAT WASHER
RUBBER STOPPER
DRILL FOR BOLT '
FLAT WASHER
BOLT
EXPANSION PLUG
RUBBER STOPPER
DRILL OUT TO NECESSARY DIA.
SEAL CAP
PIPER NAVAJO SERVICE MANUAL
387
4.20
DIA.
.19 DIA. HOLES
- 6 EQUALLY SPACED
.125 THICK STOCK
COMBUSTION HEAD OPENING
A
C
STOCK
NOZZLE OPENING COVER PLATE
Figure 13-24. Suggested Design for Seal Plate, Plugs and Caps
for Combustion Tube Leakage Test
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:
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 45 degree position as shown in Figure 13-25.
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.
Revised: 10/12/83 HEATING AND VENTILATING SYSTEM
5C14