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October 11/02
Revision 8
As Combined system pressure builds to 1500 psi, its pressure switch
opens, causing the amber CMB HYD FAIL message to be removed from
CAS. In addition, the system’s low pressure relay is de-energized.
Conversely, as pressure falls to 800 psi, the pressure switch closes,
causing the amber CMB HYD FAIL message to be displayed on CAS and
the system’s low pressure relay to be energized. (See Section 2A-29-30,
Auxiliary Hydraulic Systems, for a description of the low pressure relay.)
As Flight system pressure builds to 1500 psi, its pressure switch opens,
causing the amber FLT HYD FAIL message to be removed from CAS. As
pressure falls to 800 psi, the pressure switch closes, causing the amber
FLT HYD FAIL message to be displayed on CAS.
NOTE:
Automatic operation of the utility pump is not possible
with Combined system pressure greater than 800 psi
or with Flight system pressure less than 2000 psi.
H. System Filter Manifolds:
(See Figure 8 and Figure 9.)
The Combined and Flight hydraulic systems each have a dedicated filter
manifold located in the tail compartment (Combined on left side, Flight on
right side). Each manifold consists of three filters: main pressure, main
return and engine pump bypass.
Differential Pressure Indicators (DPIs) for each filter provide a visual
means of noting filter bypass by causing a red indicator on the DPI to “pop
up” when the pressure differential between the filter inlet and outlet
exceeds a preset value. The DPI indicator may be reset for monitoring or
troubleshooting as required.
As fluid flows from the hydraulic pump, it passes through the main pressure
filter. This filter is a “non-bypass” filter, meaning there is no alternate path to
bypass the filter element; fluid will continue to flow through the element,
though at reduced rates.
The main return and engine pump bypass filters are bypass type filters in
that a relief valve is incorporated. If the filter element begins to clog, the
pressure differential between the filter inlet and outlet opens a relief valve,
allowing the fluid to bypass the filter element.
I. System Accumulators:
Each system contains an accumulator installed between the main pressure
filter and the using systems to damp any pressure surges caused by the
associated engine driven hydraulic pump or the using system. Each
accumulator is a 50 cubic inch (0.8 liter) capacity cylinder charged with
nitrogen to 1000 psi at 70° F (21.1°C). Filler valves and pressure gauges
for the accumulators are installed on the ground test panel (Figure 10).
Each accumulator cylinder contains a free moving piston that divides the
cylinder into two chambers. One chamber contains the nitrogen charge
while the other contains pressurized fluid from the hydraulic system. As
pressurized fluid acts against the piston, it compresses the nitrogen
charge, providing shock damping by absorbing pressure transients. Should
pressure within the accumulator exceed 3850 psi, a relief valve will open to
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-29-00
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October 11/02
Revision 8
vent excess pressure.
J. Pressure Relief Valves:
The Combined system and Flight system each contain a pressure relief
valve to prevent system overpressurization. The Combined system relief
valve is installed in the left main wheel well while the Flight system relief
valve is installed in the tail compartment.
If system pressure exceeds 3850 psi, the relief valve opens to route system
pressure back to the respective reservoir through the main return filter. The
using systems are still supplied with pressurized fluid. When system
pressure falls to 3200 psi, the valve closes.
K. Ground Test Panel:
The ground test panel (Figure 10) is located on the underside of the
aircraft, just forward of the tail compartment door. It contains a reservoir fill,
pressure and suction quick disconnect group for both the Combined and
Flight systems. It also contains an accumulator air filler valve, accumulator
pressure gauge and reservoir quantity gauge for each hydraulic system.
L. Replenishing System:
The Combined system and Flight system reservoirs can be replenished
through use of a hydraulic replenisher panel (Figure 11) located in the tail
compartment. The reservoir to be serviced is selected manually with a
control valve, with actual replenishment taking place through use of a hand
pump. Reservoir quantity can then be viewed on the hydraulic quantity
indicator (with hydraulic power applied). Procedures for Combined system
and Flight system hydraulic reservoir servicing can be found in Chapter 9:
　
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