2900 Selma Highway, Montgomery AL 36108 USA
PH: +1.334.386.5400 (option 2) FAX: +1.334.386.5450 WEB: www.hartzell.aero
Page | 22
MM10001
Dated 1/1/08
Rev L dated 5/21/15
Apply 6.0±.5 psi to the combustion chamber through the combustion air pressure
supply assembly as shown on the test set-up diagram, Figure 26. After the pressure
reaches 6.0±.5 psi and stabilizes, close off the shutoff valve removing air to the
supply line. This can be accomplished by turning the air pressure regulator all the
way off relieving all pressure to the shutoff valve. (This shut off valve should be
checked for leaks prior to the start of testing as should all connections.) Start the
timer. After 45 seconds, the pressure in the combustion chamber must exceed 1.0
psi. If the pressure decays to less than 1.0 psig before the 45 seconds, a leak is
present either in the combustion chamber or the seals. Re-check all the seals
installed on the combustion chamber for leaks and rerun the pressure decay test.
If the heater continues to show rapid pressure decay of the combustion chamber, the
heater must be removed from the aircraft, and a more complete inspection be made
to determine the location of the leak.
After the heater is removed from the aircraft, conduct the pressure decay test again to
check for leaks at the spark plug seat, the fuel feed inlet gasket, screw heads and
weld seams. High temperature PERMATEX
137W or equivalent may be applied
to screw threads to stop leaking, if required. If leakage is from the stainless chamber
and not gaskets, seals, spark plug or screws, the combustion tube must be replaced.
NO REPAIRS ARE ALLOWED TO THE COMBUSTION CHAMBER!
8.6.3 Combustion Air Pressure Switch Testing (See Figure 27)
NOTE: Testing of the combustion air pressure switch is recommended each time the PDT is
accomplished: Use an air pressure source that can be controlled in a range of zero to
maximum 5” of water or damage to the switch will occur.
With the combustion air inlet adapter removed from the heater, attach the inlet
adapter pressure port (3/16” air tube on the larger end of adapter) to the regulated air
of the test kit (Fig. 26 A&B, 27 A&B). Airflow into this switch should build slowly
from zero to 0.5 + 0.1” of water indicated on a water manometer. Leave the vacuum
port tube (extending out of the small end of combustion air inlet adapter) open to
atmosphere during the test.
Using an ohmmeter across the switch terminals or across terminals #1 and #2 of the
heater terminal strip (#6 & #7 for terminal strips numbered 4, 5, 6, 7, 8, 10) to
determine the exact instant of switch closing. This reading should be 0.5 ± .01” of
water. If an adjustment is required, using a .100 inch square drive tool, rotate (1/8
turn at a time) the set screw in the center of the switch, clockwise to increase and
counter-clockwise to decrease setting. Several trials should be made to assure
accuracy and consistency.
Increase and decrease air pressure slowly in order to produce accurate indications.
Replace switch if not adjustable. Apply tamper/vibration seal after satisfactory
adjustment.
Following the successful completion of the pressure decay test (PDT), and the
combustion air pressure switch test. Remove all test fittings, plugs, supply lines,
etc., and re-install combustion air supply lines and drain lines which make up the
aircraft heater installation.
To Next Page
Loading...