HYDRAULIC SYSTEM
SUB-SECTION 4A
SUB-SECTION 4A
HYDRAULIC SYSTEM
SCOPE
Relief valves are provided to limit the pressure in the sys-
tem to safe operating Ievels.
The hydraulic system, as defined for this manual, includes
all the hydraulic components which are common to the
FLUSHING THE HYDRAULIC SYSTEM
various sub-systems of the machine. The components in-
cluded in this system are the pumps, rotary joint assembly,
If any evidence of hydraulic system contamination, such es
control valves, return line filters, and reservoir.
dirt, sludge, and/or metallic particles are discovered. flush
end clean the system as follows. If the cause of the con-
tamination is due to a faulty component, the component
Hydraulic schematics of complete hydraulic systems, along
must be repaired or replaced before the hydraulic system is
with a description of each system's operation, are at the rear
flushed.
of this section.
NOTE
Later in the manual, the components of each independent
hydraulic circuit within the complete system is discussed
The hydraulic oil should be warmed to normal oper-
separately. These systems include the outrigger, the boom
ating temperature before the reservoir is drained.
hoist and extension, the hoist, end the swing systems.
1. Remove the drain plug end drain the oil into a suitable
PRINCIPLES OF HYDRAULICS
container. Allow sufficient time for all the oil to drain from
the walls of the reservoir.
There are two factors that govern the operation of any
hydraulic system; namely, volume end pressure.
2. Install the drain plug. Fill the reservoir with a 50-50
mixture of kerosene and clean hydraulic oil.
VOLUME is the amount of oil that a pump will push
through the system in a given amount of time at a predeter-
3. Cycle the machine through all crane functions, and
mined pump speed. It is usually expressed in gallons per
operate the carrier steering and outrigger systems severaI
minute (GPM). Volume determines the speed of operation.
times to circulate the flushing oil throughout the hydraulic
The greater the volume, the faster a cylinder will fill with
system. Then return the machine to the travel position.
hydraulic oil and the fester its rod will move.
PRESSURE is the amount of force or work capability
4. Remove the drain plug and drain the flushing oil from
exerted by the hydraulic oil on all parts of the system
the reservoir. Remove the cover from the top of the reser-
opening directly to the pump when the pump is delivering
voir, and clean the inside of the reservoir manually. Replace
oil. The amount of pressure that a pump produces has no
the reservoir cover and refill the reservoir with clean hy-
relationship to the speed et which an actuator operates.
draulic oil.
Pressure is expressed in pounds per square inch (PSI).
5. Disconnect the hoses attached to the retract side of the
When the pump is merely circulating oil through a system
boom hoist cylinders, and raise the boom to its maximum
elevation slowly: This will force the flushing oil from the
which has no restrictions or is not under load, pressure is
negligible. But when a restriction or load is introduced,
cylinders.
pressure builds up almost immediately. The pressure will
continue to increase until the restriction or load is over-
6. Reconnect the hoses to the boom hoist cylinders, and
lower the boom to the horizontal. Add clean oil to the
come, the pump reaches the limit of its capacity, or some
portion of the system ruptures end relieves the pressure.
reservoir as required to maintain the proper oil Ievel.
4A-1
