99M90
21-40-01
Page: 8-13
Rev. New
Issued: May 9, 2012
I-Series Combustion Heater
Owners Manual
8.11 Fuel Pump Maintenance: (See applicable aircraft service manual)
The heater fuel pump or pumps are largely dependent on the design of the particular installation on
a specific aircraft or rotorcraft. Some installations require low pressure or high pressure pumps and
others require two pumps placed in series to obtain the pressure and flow required for supplying
fuel from a tank to the heater. The information is typical and is an example of many heater
installations. (See Figure 8.7 & 8.8)
A. Removal: (Typical)
1.
Remove access panels required to reach the fuel pump assembly. Many aircraft will have
heater fuel pumps located away from the heater assembly or in isolated locations. Refer
to the aircraft or rotorcraft maintenance manuals as necessary to locate and remove
them.
2.
Remove all electrical power. Shut off the fuel supply to the pump; disconnect electrical
lead and fuel lines. Provide a method to catch residual or spilled fuel Exercise care
to avoid losing the insulator in the electrical connector. Unless the fuel lines are rigid
enough to remain in their original locations, be sure to cap and tag them for proper
connection during reinstallation.
3.
Remove the attaching bolts from the fuel pump bracket and remove the fuel pump from
the aircraft.
4.
The HET P/N 99M91 Overhaul & Maintenance manual steps in “disassembly” must be
followed to remove fuel pump components.
B. Inspection and test: (Typical)
1.
Inspect all parts visually for damage.
2.
Inspect the fuel pump electrical resistance by connecting an ohmmeter between the
connector terminal and ground on the pump housing. Resistance should be between
19.0 and 30.0 ohms for 24 volt models, and 4.8 to 12.0 ohms for 12 volt models. If
resistance is not within limits, replace the pump assembly.
3.
Low pressure pump as shown in Figure 8.7 have a filter screen which may be accessed
by removal of the bottom cover.
4.
Complete cleaning and testing may be done in accordance with the appropriate chapter in
the overhaul manual.
C. Installation: (Typical)
1.
The HET P/N 99M91 Overhaul & Maintenance manual steps in “assembly” must be
followed to reinstall fuel pump components prior to aircraft installation.
2.
Attach the fuel pump to the aircraft structure member with the two attaching bolts. The
radio noise filter bracket must be attached with one of these bolts. Make sure a good
electrical ground is present and proper polarity connection made.
3.
Remove tags and caps. Connect the inlet and outlet fuel lines and tighten them securely.
4.
Connect the electrical lead at the radio noise filter connection. Be sure the insulator is
in place and the connector is locked securely.
5.
Run the pump for a few minutes to check for fuel leaks.
6.
Install access panels. Refer to the latest revision of the aircraft or rotorcraft service or
maintenance manuals as required.
