TM 55-4920-394-13&P
1-16. Main Hydraulic Pump (4, Fig. 1-2). The main hydraulic pump supplies fluid at high pressure for testing
of aircraft hydraulic circuits. The pump consists of a high pressure pump section and integral boost pump
section. The pump contains a manual volume control for varying the output volume and a compensator control
to regulate the output volume by changing the stroke length of the pumping pistons. Change in piston stroke
length is controlled by system pressure so that when the pump is operating at a pressure less than the
maximum setting of the compensator control, the pump delivers full volume. When the system pressure
reaches the compensator control setting, the pump output is automatically reduced to the amount of flow
required to maintain this pressure throughout the system. The compensator control provides an adjustable
range of 500 to 5000 psig with flow varying to 27 gpm maximum. The volume control permits regulation of
maximum volume output by limiting the angle of a cam plate through a threaded mechanism within the pump.
The return line for the test system also includes a flowmeter to monitor fluid flow.
1-17. Hydraulic Fluid Reservoir (2, Fig. 1-4). The reservoir is designed to supply fluid to the system during
operation in " tand" position of the reservoir selector valve and to supply fluid to the fill system. A filler neck-
s
cleanup cover is located on the top of the reservoir allowing manual filling. A fluid level indicator is also
provided on the control panel.
1-18. Oil Cooler (3, Fig. 1-4). The oil cooler consists of a heat exchanger type cooler with a cooling fan. The
fan draws air through the cooler for cooling the hydraulic oil. Air is exhausted through vents in the cabinet.
1-19. High Pressure Filter (3, Fig. 1-3). A filter is located in the output line of the system. A five micron
filter element gives the pressurized fluid a final cleaning before outlet to the aircraft.
1-20. Low Pressure Filter (2, Fig. 1-3). A low pressure filter in the outlet line from the boost pump is
incorporated to clean hydraulic fluid of contamination before entering the high pressure pump section. The
filter is readily maintained through access doors for replacement of filtering elements. A drain is provided for
the low pressure filter.
1-21. Fill Pump System. This system is used to fill the test stand hydraulic system with fluid in the
preparatory operation of readying the test stand for scheduled operations. It also functions to fill the aircraft
reservoir with pressurized fluid from the stand reservoir. The system includes an electric motor driven fill pump
(2, fig. 1-2) with filter (5), system actuating valves (30, fig. 1-5), relief valve (33) and check valve (14).
NOTE
Reservoir selector valve must be in "ship" reservoir position when
performing filling operation.
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