Fuel Regulator And Shutoff Valve - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
382
ADJUSTING SCREW
Figure 13-7. Fuel Regulator and Shutoff Valve
13-9. DUCT SWITCH. (Refer to Figures 13-8 and 13-9.) This switch is installed in the ventilating air duct
downstream from the heater to sense the ventilating air outlet temperature. To select the desired cabin
temperature, the switch may be adjusted manually from a high of 250°F ± 10
°
downward through a range
of 146
0
F ± 60. The switch has a differential of 100F + 5
°
at any given setting. On later installations an
override switch has been added to the duct system switch to override the duct switch at the last portion of
its travel to the high heat position and cancel the duct stat control only at the maximum heat position.
13-10. COMBUSTION AIR BLOWER AND PRESSURE SWITCH. This centrifugal-type blower supplies
air to the combustion chamber of the heater. Performance of the combustion air blower is assisted by the
use of ram air during flight. A differential pressure switch cuts off the heater operation whenever the
fuel-air mixture is not appropriate for efficient heater operation. This switch is set to activate at 0.5 inches
of water ± 0.3 inches. On 39D59 heater system No. 2 and B39D59 heater system installations another
pressure switch is incorporated in the heater system to shut off the combustion air blower whenever there is
enough ram air to operate the heater without the blower. This switch is set to shut off the blower at 5 ± .3
inches of water, when the air pressure increases. When air pressure decreases to 2.5 ±.5 inches of water, the
blower starts. Both switches operate off the same differential pressure, are normally closed, and will open
when pressure increases.
13-11. VENTILATING AIR BLOWER. This blower is attached to the inlet end of the heater assembly and
provides a source of ventilating air through the heater. Ram air from the ventilating air intake scoop is used
during flight.
13-12. HEATER SAFETY LIMIT SWITCH. Located in the heater is a heat limit switch, which acts as a
safety device to render the heater system inoperative if a malfunction should occur causing excessively high
temperatures. This control is located in the downstream end of the vent jacket, with the reset button on the
heater shroud. It is reached only through the access panel on the right side of the nose section. Insure that the
malfunction causing the overheat condition is corrected prior to future heater operation. The cycling switch is
located in the downstream end of the vent jacket, operates to control the outlet air temperature from the
heater. This switch cycles the heater on and off to maintain the set temperature and is adjustable.
Reissued: 10/12/79 HEATING AND VENTILATING SYSTEM
5B12