Specifications

SECTION II
MODEL 560 AIRPLANE AND SYSTEMS
PUMPS
Hydraulic pressure is provided by two positive displacement engine-driven pumps, each mounted on the
engine accessory case. Either pump is capable of supplying enough pressure to operate the gear, flaps,
speedbrakes, two-position horizontal stabilizer and reversers. From each pump, hydraulic fluid is routed
through filters and flow switch check valve assemblies to the bypass valve and relief valve. In the event
that either pump output should drop to less than 0.45 ±0.10 gallons-per-minute, (GPM), the respective LO
HYD FLOW annunciator panel light will illuminate. The light will extinguish when pump output reaches a
minimum of 1.33 GPM.
HYDRAULIC SYSTEM INDICATING
The hydraulic indicating systems are comprised of three separate warning systems: A low-fluid
quantity warning system to indicate when fluid in the reservoir is at minimum operating volume (HYD LOW
LEVEL); a fluid flow warning system(s) to indicate low or no flow of fluid from either/both hydraulic pumps
(HYD FLOW LOW LH) (HYD FLOW LOW RH); and a pressure indicating system to indicate hydraulic
pressure buildup during actuation of a hydraulic system component (HYD PRESS ON).
Hydraulic Low Fluid Quantity Warning System - The hydraulic low-fluid quantity warning system
incorporates a low-fluid warning switch mounted on the hydraulic reservoir visual indicator; a warning light
HYD LOW LEVEL located on the annunciator panel and necessary wiring. The hydraulic reservoir fluid
capacity is measured by volume of fluid. A visual indicator on the end of the reservoir is scaled at EMPTY
(5 Cubic Inches), REFILL (38 Cubic Inches), FULL (125 Cubic Inches) and OVERFULL (150 + Cubic
Inches). The low-fluid warning switch is mounted at approximately the REFILL mark with the switch actuator
roller riding on the visual indicator rod. The rod moves according to the volume of fluid in the reservoir. The
switch is electrically connected to the warning light HYD LOW LEVEL on the annunciator panel. The
warning switch is a micro type switch, held to a bracket with two screws and nuts.
Hydraulic Fluid Flow Warning System - The fluid flow warning system incorporates two check valve-
flow switches located on the forward side of the aft engine carry- thru beam; two warning lights, HYD FLOW
LOW LH and HYD FLOW LOW RH, located on the annunciator panel and necessary wiring. The left and
right fluid flow warning systems are independent of each other, but function identically. The check valve
portion of each flow switch check valve prevents fluid flow from one engine pump to the other. The flow
switch portion of each flow switch check valve is normally closed (no-flow), completing the electrical circuit
to the warning light. At a predetermined fluid flow through the unit, the flow switch opens, extinguishing the
warning light. Refer to Flow Switch Check Valve - Maintenance Practices.
Hydraulic Pressure Indicating System - The purpose of the hydraulic pressure indicating system is to
inform the flight/maintenance crew that the hydraulic system is pressurized during landing gear actuation,
flap actuation, speed brake actuation or thrust reverser operation. When the flap actuation, hydraulic system
is in a no pressure condition (bypass valve open to return), the pressure indicating switch is open; the
annunciator light HYD PRESS ON is extinguished. When the landing gear, flaps, speed brake or thrust
reverser is actuated, the bypass valve also closes and pressure is built up to operate the selected system.
As the pressure increases toward 1500 PSI (maximum system pressure), the pressure switch closes at 185
PSI maximum and completes the electrical circuit to illuminate the annunciator light HYD PRESS ON. After
the selected hydraulic system completes actuation, the bypass valve opens, bypassing pressure to return.
As the pressure decreases, the pressure switch opens at 155 PSI, +5 or - 5 PSI, minimum and
extinguishes the annunciator light. Refer to Hydraulic Panel Assembly and Components - Maintenance
Practices, for removal/installation of the pressure switch.
NORMAL OPERATION
When either the landing gear, flaps, speedbrakes, two-position horizontal stabilizer or thrust reversers are
actuated, a bypass valve in the return line closes enabling the system to pressurize to
1500 PSI. At the
same time, the respective control valve opens, allowing flow to go to the selected system. A relief valve
which maintains system pressure at 1500 PSI is in parallel with the bypass valve. The relief valve cracks at
1350 PSI and is fully open at 1500 PSI. The HYD PRESS light illuminates on the annunciator panel any
time the system is pressurized. Once the selected cycle is complete, the respective control valve closes,
the bypass valve opens and the system reverts to the low pressure, open center state.
I 56OMB-01 Configuration AA 2-21