Pneumatic Deicing System Operational Check; Electrical Test; Pressure Leakage Test; Pneumatic System Adjustment - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
On all models a pneumatic relay shutoff valve assembly is installed behind the instrument panel and
above the copilot's rudder pedals. This valve protects the pilot's gyro instruments from the high deicer boot
inflation pressure and a solenoid on this valve shuts off the copilot's gyro air pressure only for the duration
of the deicer inflation cycle.
A ply of conductive neoprene is provided on the surface to dissipate static electric charges. These
charges, if allowed to accumulate, would eventually discharge through the boot to the metal skin beneath,
causing static interference with the radio equipment and possible punctures in the rubber. Also, such static
charges would constitute a temporary fire hazard after each flight.
14-63. TROUBLESHOOTING. In the utilization of the troubleshooting charts at the end of these
instructions, it must be assumed that the engine driven pneumatic pumps and the airplane electrical system
are operational. It is further assumed that the deicer system installation was made in an approved manner.
14-64. OPERATIONAL CHECK. The pneumatic deicing system should be checked at least every 100
hours. This check can be done on the ground. A visual inspection should be performed to determine the
condition of the deicer boots, and any areas in need of repair should be taken care of before continuing
with the operational check of the system.
With one engine operating, activate the deicing system switch. The pressure will fluctuate as the tubes
inflate and deflate. Check the pneumatic pressure gauge. If pressure is satisfactory, observe the operation of
the deicers carefully for evidence of malfunctioning. Look for tubes which leak or fail to inflate and deflate
properly. Repeat the procedure for the other engine.
14-65. ELECTRICAL TEST. With engines off, turn airplane battery switch to ON position.
a.
Timer: Activate the deicer system switch. The timer should begin to operate immediately and
complete one full cycle of the system. If the timer does not function:
1. Reset circuit breaker and recheck.
2. Check circuit from power source, through circuit breaker, to switch, to timer, to ground.
3.
Replace timer.
b. Solenoid Valves: Check solenoid valves. Activate system switch to ON position. Solenoid valve
should be actuated immediately for 6 seconds, as evidenced by an audible "click" that can be felt if hand is
placed on a solenoid.
14-66. PRESSURE LEAKAGE TEST.
a. This test can be performed in either the left or right nacelles.
b. Disconnect the hose from the filter to the control valve at the control valve end. Connect a
source of clean air to the filter hose. It is necessary to have a pressure of 18 psig to perform this test.
Observe the system pressure on the airplane's pneumatic pressure gauge.
c. Apply 18 psig pressure to the system by means of a hand operated valve; trap the pressure in the
deicer system. Observe the system for leakage. The leakage rate should not exceed a pressure drop of 3.0
psig per minute.
d. Remove test equipment and replace all system components.
14-67. PNEUMATIC SYSTEM ADJUSTMENT. The pneumatic system is adjusted to provide adequate
pressure for the airplane instruments and any other equipment. Refer to Section X of this Service Manual
for the proper procedure.
14-68. COMPONENT MAINTENANCE AND REPLACEMENT.
14-69. FILTER REPLACEMENT. There are four air line filters installed in the pneumatic system of this
airplane. Two inline filters (#1J4-6) and two air filters (#1J1-3). The following instructions will cover the
removal and installation of these filters.
Revised: 10/5/83
ACCESSORIES AND UTILITIES
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