5-75. APU FUEL TRANSFER PUMP - Continued
Transfer pump failure is usually due to a leaking diaphragm, valve or valve gasket. A kit is
available for replacement of these parts. Because the extent of wear cannot be detected by the
eye, replace all parts in the kit. If the diaphragm is broken or leaks fuel, check for diluted
crankcase oil, replace as required.
Occasionally, failure is due to a broken or weak diaphragm spring or wear in the linkage. In this
case, replace the worn parts or install a new pump.
Dry cleaning solvent P-D-680 is potentially dangerous. Avoid
repeated and prolonged breathing of vapors and skin contact
with the liquid. Do not use near open flame, arcing equipment
or other ignition sources. Always wear eye protection and
protective clothing. The flash point of P-D-680 is 100 to 138
deg. F (38 to 59 deg. C).
When installing a new diaphragm, soak it in fuel before assembling. Insert the diaphragm spring
(4) and soaked diaphragm (3) into the pump body (5).
If removed, insert the rocker arm link (6) and rocker arm (7) into the body (5) and hook it over the
diaphragm pull rod (8). Align the rocker arm with the rocker arm link pin hole and drive in the pin
(9). The priming lever (1 0) must be in its lowest position, as illustrated, when installing the rocker
Compress the rocker spring (11) and install between the body and rocker arm.
Insert the valve cages (12), gaskets (13) and valve cover plate (2). Position the inlet valve (14)
with spring showing and the outlet valve (1 5) with spring in the cover recess (if valves were
Assemble the cover to the body (5) with notch marks lined up. Install the screws (1) but do not
The diaphragm must be flexed or it will deliver too much fuel
Push the rocker arm (7) in full stroke and hold in this position to flex the diaphragm.
Tighten the six cover screws alternately and securely, then release the rocker arm.
d. Follow-on Maintenance.
Install fuel transfer pump (see para 4-216).
Using a pressure gauge or manometer, test pump for 3-1/4 to 4-1/2 psi (22.4 to 31 kPa) outlet