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Copilots Display Unit (PDU)

Pressurizing & Overspeed Unit (POU)
D-39 7. LEARNING STEP/ACTIVITY No. 7. Identify the operational characteristics of the engine fuel system.

a. T700 Fuel System Overview- The UH-60 fuel system is designed to provide the proper fuel flow to the engine under all operating conditions including starting, idle, normal flight, and maximum power.
Components of the engine fuel system include (in order of fuel flow) an engine driven boost pump, fuel filter, fuel pressure sensor, hydromechanical unit (HMU), liquid to liquid cooler (oil cooler), pressurizing and overspeed unit (POU), 12 fuel injectors, and 2 primer nozzles.
The UH-60 fuel system was designed to operate in a "suction mode", meaning the engine driven boost pump suctions fuel from the cell to feed the engine.  Should a leak occur in the main fuel supply lines no fuel would leak or spray from the hole, air would be drawn in.  The draw back to operating "pressurized" verses "suction" is that a break or hole in the main fuel supply line now results in fuel spray.

b. Fuel System Flow- Fuel originates from the fuel cells, each containing an electric submerged boost pump that can pressurize fuel to 25-27 psi. The engine driven boost pump suctions fuel at -3 to -6 psi in the suction mode from the selected fuel cell.  If the electric submerged boost pump is "ON", fuel is pumped to the engine driven boost pump in he pressurized mode. The engine driven boost pump raises the fuel pressure to 45-90 psi, and pressurizes the AGB fuel passages. Next are the fuel filter, the fuel pressure sensor (controls the #1 FUEL PRESS and #2 FUEL PRESS caution lights), and the HMU. The HMU has a high pressure vane pump that increases the fuel pressure to 400-832 psi, and varies fuel flow through a main metering valve. Main metered fuel then flows from the HMU through the oil cooler, the POU, and then to either 2 start fuel nozzles or 12 main fuel injectors.

T-700 FUEL SYSTEM SCHEMATIC

(typical both engines)
FUEL
SELECTOR
LEVER

30 MICRON
(18-22 PSID)
9PSI
(8-10 PSID)
P O U
#2 fuel
selector
valve

Electrical
Control
Unit

FUEL BOOST PUMP CONTROL
ON ON
NO.1 NO.2
PUMP

PUMP
OFF OF F
submerged
boost

submerged
boost
pump

pump
(electric)

(electric)
#1 FUEL CELL #2 FUEL CELL
M
A
I
N

F U E L
P U R G E
A G B
vane pump (Ng driven)
V.P.
H
PCL opens
vapor vent
valve

M
metering PCL sets/limits
valve
U
PCL can
power setting lock out trq. motor
　
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