Figure 4-9.—Model HSU-1 fluid service unit.
The original fluid container serves as a reservoir
for the H-250-1 servicing unit. This container is not
opened until it is placed in the unit, and the handle
assembly pressed into a locked position. When the
handle is locked, the can is sealed into the unit by
cleanly piercing its top and bottom. This action
automaticallyy destroys the can’s potential for reuse.
The H-250-1 servicing unit is equipped with a top
piercing pin, which is drilled to provide the can with
atmospheric venting through a 5-micron filter. Also,
it has a check valve to minimize airborne particulate
and moisture contamination. The lower piercing pin
is drilled so the hydraulic fluid can reach the pump
through a passage in the base casting and a 3-micron
filter. The filter is a nonbypass type. When it
becomes loaded, the unit is inoperative. The filter
housing is designed so that the pump won’t operate if
a filter element has not been installed.
A pressure gauge, an air trap, and a manual air
bleed valve are attached directly to the pump
assembly base. The air trap automatically removes
any air present in the fluid at the pump chamber and
retains it in a separate trap. Air collected in the trap is
vented from the unit by manually operating a
spring-loaded, air bleed valve.
The H-250-1 servicing unit has an 8-foot service
hose that is equipped with a 3-micron, in-line filter
connected at the discharge end, which prevents
reverse flow contamination through the hose. There
are several types of disconnect fittings on the
reservoir service units of naval aircraft. There are no
mating fittings provided with the unit. Each activity
must procure and install the disconnect fitting
required for compatibility with the aircraft supported.
Both male and female fittings are procured so that
half can be installed on the hose end and half on the
bracket provided. The bracket-mounted fittings will
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