Figure 12-13.--Double-action hydraulic hand pump.
3. Select an appropriate subsystem to operate, and
illustration, check valve (A) closes and check valve (B)
place its selector valve in an operating position.
opens.
4. Actuate the hand pump handle until the unit
Fluid from the reservoir then flows into the
being operated has completed its movement. Check the
cylinder through inlet port (C). When the piston is
pressure gauge for a drop in system pressure.
moved to the right, check valve (B) closes. The
pressure created in the fluid then opens check valve
NOTE: Air in emergency systems will cause the
(A), and fluid is admitted behind the piston. Because
pump handle to spring rapidly to the other end of the
of the space occupied by the piston rod, there is room
stroke.
for only part of the fluid; therefore, the remainder is
5. If a pressure drop is indicated, check the system
forced out port (D) into the pressure line. If the piston
for leakage before removing the pump for repair or
is again moved to the left, check valve (A) again closes.
replacement.
The fluid behind the piston is then forced through
outlet port (D). At the same time, fluid from the
6. Observe the hand pump handle for piston creep,
reservoir flows into the cylinder through check valve
which indicates that the pump should be removed for
(B). Thus, a pressure stroke is produced with each
repair or replacement.
stroke of the pump handle.
Removal, replacement, and operational check of
Hand pumps are examined frequently for leakage,
hand pumps should correspond to the procedures
general condition, and efficiency in operation. To
recommended in the specific MIM.
check the operation of a hand pump, the following
procedure is recommended:
Power-Driven Pumps
1. Connect a direct-reading hydraulic pressure
Power pumps are generally driven by the aircraft
gauge into the emergency hand pump pressure line.
engine, but may also be electric-motor driven. Power
2. Insert and lock the hand pump handle in the
pumps are classified according to the type of pumping
pump actuating socket.
action used, and may be either the gear type or piston
12-13
