TM 1-4920-446-13 & P
b. A thermoswitch in the high pressure pump shuts down the unit when fluid temperature exceeds 160°F.
c. Low pressure switches protect the high pressure pumps against cavitation due to low inlet pressure or boost
pump failure. If the pressure drops below 40+5 psig, the unit is automatically shutdown.
d. Check valves prevent reverse flow of hydraulic fluid.
e. Differential pressure switches across filter ports of the high and low pressure filters illuminate warning lights on
the control panel to indicate a clogged filter.
f. A circuit breaker is provided for overload protection of various circuits. Refer to Figure C-4 for location of electri-
cal components and Figure 1-3 for wiring schematic.
g. Complete instrumentation and controls are located on the control panels. Refer to Chapter 2, Figure 2-2 and Ta-
ble 2-1 for description of function and location.
1-21. Electrical System (Figure 1-3). The system provides the circuits and control for proper functioning of electrical
components. Electrical power is supplied by an external source through the external electrical cable.
1-22. Equipment Data. The equipment data in Table 1-1 summarizes the specific capabilities and limitations on
SECTION III. PRINCIPLES OF OPERATION
1-23. Simplified Principles of Operation. (Figure 1-4.) The boost pump receives fluid from the aircraft through the
suction return port and flowmeter. The output of the boost pump is passed through the low pressure filter to the suction
side of the high pressure pump. The boost pump pressure is controlled by the low pressure relief valve. The output of
the high pressure pump is passed through the high pressure check valve, high pressure filter, flow control valve, and
pressure outlet to the aircraft. The output pressure is controlled by the high pressure relief valve and a compensator
control on the high pressure pump. The output is controlled by the flow control valve, and regulated by a volume con-
trol on the high pressure pump.
Before operation ensure test stand is wired for 220 volt operation.