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 750 to 5000 psig with the flow varying to 30 gpm maximum.
Further reduction to 500 psig can be achieved by adjusting the minimum volume stop adjustment located on the side of
the main pump. 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 lines for the test system also include a flowmeter located on
the control panel (figure 1-2) to monitor fluid flow.
Reservoir. The reservoir (figure 1-2) supplies hydraulic fluid for test stand functions including filling and bleeding of test
stand system, and filling of aircraft system under test. A cleanout cover is accessible on the top of the reservoir. A fill
neck, which is located on top of the reservoir, allows manual filling of reservoir. A fluid level indicator is provided on the
Oil cooler. The oil cooler (figure 1-2) consists of a two-section radiation type heat exchanging cooler with a cooling fan.
The cooling fan is driven by a fractional horsepower motor. Both sections of the cooler serve the hydraulic system. The
fan draws air through the cooler for cooling the hydraulic oil. Air is exhausted through vents in the cabinet.
High pressure filter. A filter (figure 1-2) is located in the high pressure output line. A micron filter element gives the
pressurized fluid a final cleaning before outlet to the aircraft. A warning light displayed on the operator's control panel
(figure 1-1) indicates a high differential pressure condition between the filter inlet and outlet should the filter elements
become clogged with sediment removed from the hydraulic fluid.
Low pressure filter. A low pressure filter (figure 1-2) in the outlet line from the system boost pump is incorporated to
clean hydraulic fluid of contamination before entering the high pressure pump section. The filter is maintained by
removing top panel for replacement of the filtering element.
A drain is provided for the low pressure filter.
Fill pump system. (refer to figures 1-3 and 1-4). This system is used to fill the test stand hydraulic system with fluid in
the preparatory operation of readying the test stand for scheduled operation. It also functions to fill the aircraft reservoir
with pressurized fluid from the stand reservoir. The system includes an electric motor driven fill pump with filter, system
actuating valves on control panel, relief valve and check valve. This filter is provided with a differential pressure ( P)
light on the control panel to indicate clogging.
Bleed system. (refer to figure 1-4). The test stand hydraulic system incorporates a bleed valve (4) to eliminate
entrapped air from the system and sight glass to observe the fluid flow to the hydraulic reservoir. The valve is actuated
by pressing in on the spring loaded valve stem with a push-type handle on the control panel. Air and fluid are bled to the
reservoir from the low pressure filter and the cooler. A thermal relief valve in parallel with the bleed valve prevents
increased pressure in the cooler and filter caused by thermal expansion.