AIRCRAFT OPERATING MANUAL
DHC - 7
8
SYSTEM DESCRIPTION
Revision
Date
: 0
: July 1999
PT. PELITA AIR SERVICE
AOM
P a g e
: 8.12
: 1 of 7
HYDRAULIC POWER SYSTEM
GENERAL
Two independent hydraulic power systems supply pressure to operate various systems as
shown in figure 1-9-1. No. 1 (left) system is pressurized by hydraulic pumps driven by No.
1 and No. 2 engines and No. 2 (right) system is pressurized by pumps driven by No. 3 and
No. 4 engines. The No. 1 system has a total capacity including reservoir of 16.4 U.s.
quarts (15.5 liters). No. 2 system has a total capacity including reservoir of 22.5 U.S.
quarts (21.3 liters). The nominal operating pressure for both systems is 3000 psi. Either
system can be sustained by one pump if a failure of the other pump or an engine
shutdown occurs, Each system has its own ground connections for ground servicing
purposes. Firewall shutoff valves in the engine nacelles, operated by their associated
emergency fuel shutoff controls, provide for hydraulic fluid supply closure to their
respective engine driven pumps in the event of fire.
A pressure indicator and fluid quantity indicator for each system are located on the
captain’s instrument panel. Low pressure warning is provided by an ENG HYD PUMP
caution light which is illuminated on a decreasing pressure of 2000 ± 100 psi.
An Independent, hand pump operated system, located in the nose gear well, is provided
for emergency lowering of the nose gear. The capacity of the auxiliary reservoir is 1.25
U.S. quarts (1.2 liters).
ENGINE-DRIVEN PUMP LOW PRESSURE
A pressure switch in each main system pump pressure line closes at 2,000 ±50 psi
decreasing pressure to illuminate the #1, #2, #3, or #4 ENG HYD PUMP caution lights on
the caution lights panel. These lights will be illuminated prior to engine start.
RESERVOIR QUANTITY
A separate reservoir quantity indicating system is provided for the No. 1 and No. 2 system
hydraulic reservoirs. A transmitter attached to each reservoir provides fluid quantity
indications on the HYD QTY indicators located on the pilot’s instrument panel .
NOTE
Blue radials on the indicators represent full and refill levels only when fluid temperature is
70° F.
The fluid is near ambient temperature several hours after engine shutdown. Prior to that
time, the hot fluid will be at a higher level in the reservoir, and judgment must be exercised
when determining minimum dispatch quantity.
Summary of Contents for Dash 7
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