Hartzell CD15K - 8.6 HEATER PRESSURE DECAY (PDT) AND COMBUSTION AIR SWITCH TEST; 8.6.1 Equipment Required to conduct the pressure decay inspection test:; 8.6.2 Combustion Tube Pressure Decay Test (Read entire instructions before beginning PDT.)

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MM10001
Dated 1/1/08
Rev L dated 5/21/15
8.6 HEATER PRESSURE DECAY (PDT) AND COMBUSTION AIR SWITCH TEST
Purpose: Condition evaluation of the combustion chamber and combustion air switch. Inspection
shall be made at the 1,000hr/4yr inspection and thereafter each 250 hours or four years, whichever
comes first. This test can be accomplished while the heater is installed with a minimum of
accessory disconnection. For convenience, the heater assembly could be removed from the
aircraft to conduct the pressure decay test. It should be kept in mind that some leakage is expected
due to gasket or screw seal. However “NO COMBUSTION TUBE LEAKAGE IS
PERMISABLE!” If during inspection the integrity of the welded combustion tube itself is in
question, the heater should be removed and further inspected.
NOTE: Be sure test kit calibration is up to date.
8.6.1 Equipment Required to conduct the pressure decay inspection test:
• “Pressure Decay Test Kit” P/N 70100,
• “Pressure Tester” P/N 70200
• Other FAA approved equipment.
8.6.2 Combustion Tube Pressure Decay Test (Read entire instructions before beginning PDT.)
 To conduct the pressure decay test, the heater must be sealed at all openings into the
combustion chamber assembly. The openings into the combustion chamber include
the combustion air inlet tube, fuel drains (one or two), and the exhaust tube. To
obtain access to the heater exhaust tube in some aircraft, you may have to loosen and
remove aircraft heater mounted exhaust tube and exhaust tube shroud from the heater
assembly before inserting exhaust seal bulb.
 Install pressure seals on combustion chamber using the parts supplied in the
combustion pressure decay test kit. Remove the combustion air inlet adapter (Figure
26A), having two hoses attached from the combustion air switch.
 Loosen the overboard drain line from the heater and install a cap or plug.
 Visually inspect exhaust tube of heater for obstructions. (See Figure 28) Check
exhaust inner surface for sharp projections that could damage the rubber bulb of the
exhaust tube seal during inflation.
 Attach the correct size exhaust seal expansion bulb to the pressure supply system as
shown in Figure 26. Use the largest size expansion bulb that will fit the exhaust
inside diameter.
 NOTE: After the seal is properly inserted into the exhaust tube (see figure 28), and
while holding it in place, slowly inflate the seal to 70 ±5 psig pressure using the
regulated supply air as shown in Figure 26. When properly installed and inflated, the
seal will hold itself in place.
 Install and tighten in place (Figure 26) the combustion air pressure supply assembly
using the hose clamp. Attach air supply line as shown. Attach a supply line to the
combustion air pressure supply assembly fitting (see figure 26) Slowly apply 3 psi
of air pressure from the regulator as shown in test set-up diagram. If leakage is
suspected at PDT seals, check with a mixture of soapy water sprayed on seals and
look for bubbles. Pressure in the exhaust seal expansion bulb may be increased to 95
psi to achieve a leak proof seal.