Timer Maintenance; Inspection - Piper Cheyenne IIIA Airplane Maintenance Manual

PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. Airfoil - Description and Operation (continued)
4. Pneumatic Regulator Adjustment
To gain access to the pneumatic pressure regulator on the right of the fuselage centerline, remove
the floorboard access panel at Fuselage Station 156.00.
The adjustable regulator provides appropriate pressure for the pneumatic system. An adjustment
screw on the outboard end of the valve body is accessible by removing the thermoplastic vent cap
from the outboard end of the regulator. Proceed as follows to check regulator operation:
WARNING: ALL SAFETY PRECAUTIONS MUST BE OBSERVED WHEN STARTING AND
OPERATING ENGINES. ENSURE AIRCRAFT IS PROPERLY RESTRAINED WHEN
USING FULL POWER SETTINGS. REFER TO PILOT'S OPERATING HANDBOOK
FOR OPERATING INFORMATION.
(a) Start both engines and place both right and left engine bleed air switches in the ON position.
Establish steady airflow in cabin. If door is closed, ensure door seal inflates.
(b) Cycle deicer boots and observe system pressure on cockpit pneumatic gauge. With engines at
maximum power 90% Ng, the pressure must not exceed 20 psig. With one engine operating at
85% Ng, pressure must not go below 16 psig.
(c) To adjust regulator, proceed as follows:
(1.) Remove appropriate floor access panel.
(2.) Loosen clamp and slide plastic vent cap off outboard end of regulator, exposing
adjustment screw.
(3.) Loosen jam nut on screw and rotate screw clockwise to increase pressure,
counterclockwise to decrease pressure.
(4.) Lock screw in position with jam nut.
(5.) Reinstall plastic vent cap on regulator and tighten clamp.
CAUTION: ENSURE VENT CAP IS REINSTALLED PROPERLY ON REGULATOR.
ENSURE HOSE FROM CAP TO FUSELAGE IS SECURE AND IN GOOD
CONDITION. IF CAP IS LEFT OFF OR NOT PROPERLY SECURED,
REGULATOR IS REFERENCED TO CABIN PRESSURE, NOT AMBIENT
PRESSURE, CAUSING REGULATOR TO ALLOW EXCESSIVE
PNEUMATIC PRESSURE TO BUILD UP IN DEICERS AND DOOR SEAL.
NOTE: New aircraft contain a pressure regulator incorporating an overboard vent fitting,
eliminating the vent cap used on earlier aircraft. Regulator adjustment is
unaffected.
5. Timer Maintenance
No field maintenance is recommended. See parts catalog for replacement or vendor for repairs.
6. Inspections
Complete a ground check of entire deicer system at least every 100 hours. To ground check
system without operating engine, disconnect pneumatic system line (3/4-inch branch line upstream
of bleed air shutoff valve) at engine and connect hose from shop air to pneumatic line with air
regulated to 22 psig. The shop air supply must be capable of delivering air 3 pounds per minute at
22 psig.
Before checking system, inspect all deicers for damage and repair according to cold patch or
vulcanized repair procedures in this section. To check system, use deicer piping diagram drawing
to determine the operating pressure and inflation time allotted for deicers.
EFFECTIVITY:
040-999
30-10-00
JaPAGE 7 Jan 10/90