CSP−900RMM−2MD Helicopters, Inc.
Rotorcraft Maintenance Manual
Page 1
Revision 25
29-00-00
HYDRAULIC SYSTEM
DESCRIPTION AND OPERATION
1. Hydraulic System
(Ref. Figure 1)
The hydraulic control system is a dual circuit
system. The system supplies pressure to three
dual circuit servoactuators to assist main rotor
flight controls operation. System 2 also
supplies pressure to a single circuit servoac
tuator to assist anti-torque/directional flight
controls operation. The hydraulic system uses
hydraulic fluid (C112) that is approved for
operations in temperatures between -40° F to
+275° F. Servicing is accomplished by using
ground support equipment, or the optional
hand pump.
Systems 1 and 2 operate nominally at 500
psig. If pressure is lost in one of the hydraulic
systems, the remaining system pump output
pressure increases to 1000 psig. Each circuit
consists of the following components:
2. Hydraulic Components
(Ref. Figure 2)
A. Variable Delivery Pumps
The two hydraulic pumps are piston type
variable displacement pumps capable of
providing flow rates up to 2.2 gpm. Each pump
is driven by an accessory drive on the main
transmission. The pump drive shaft is coupled
to the transmission accessory drive by a spline
which will shear in the event of a physical
overload.
Each pump contains nine pistons arranged
axially in a floating cylinder block. A compen
sator circuit varies pump displacement to
maintain a constant 500 psig during varying
system flow requirements, providing rapid
pump response. Mechanical stops at full flow
and full cut off positions prevent system
damage.
If pressure is lost in one of the hydraulic
systems, the functioning system's pump
compensator circuit is reset to 1000 psig. The
compensator is reset when the mis-function
ing system's pressure decreases to between
200 psig and 400 psig.
Fluid is carried through drilled passages to the
contact face of each piston shoe for lubrication,
cooling, and hydrostatic balance. This hydro
static balance reduces bearing contact
pressures, minimizing friction and wear. Other
parts are lubricated and cooled with this fluid
as it circulates at 0.02 to 0.08 gpm through the
pump and returns to the manifold/reservoir.
B. Manifold/Reservoir Assemblies
The manifold/reservoir assembly distributes
the pressurized hydraulic fluid to the servoac
tuators. The manifold/reservoir assembly is
the collection point for the fluid returns, and
contains the system operating fluid. The
manifold/reservoir assembly components are
mounted in an aluminum alloy housing. All
fluid connection fittings on the manifold/reser
voir are of the ring-lock type.
The bootstrap reservoir prevents cavitation
during high system flow demands. It main
tains a 2.4 psig minimum static pressure to
the pump when the system is shut down and
27 psig during normal system operation.
The reservoir bleed valve provides for removal
of entrapped air and prevents the reservoir
from being over pressurized above 150 psig.
The valve is a spring-loaded valve used to
bleed the system during servicing. The valve is
mounted in the housing assembly at the
highest point. CURRENT CONFIG - The
bleed valve is also used for obtaining fluid
samples.
A system relief valve prevents damage to the
hydraulic system in the event the pressure
compensator in the pump malfunctions. The
valve actuates at 1350 psig and resets at a
minimum pressure of 1150 psig.
The pressure and return filters are standard
five micron filter elements contained in
threaded filter bowls. When the filter bowl
assembly is removed a shutoff valve closes,
isolating the system fluid to prevent leakage.
A set of spring-loaded levers prevent the filter
bowl from being installed without the filter
element.
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