Manitowoc Grove RT770E, Service Maintenance Manual

Page: 52 / 357

HYDRAULIC SYSTEM RT770E
2-12 Published 11/26/2014, Control # 447-05
Troubleshooting Aids
1. Hydraulic schematics - an exact illustration of the
arrangement of the system. The schematic shows all the
components in relation to the system. The ability to
understand the schematic is important to good
troubleshooting. The schematic can be found at the end
of this manual.
2. Flowmeter - an instrument that can be connected into
the system to measure the flow of the oil in the system.
The flow is measured in gallons per minute (gpm) or
liters per minute (lpm). Normally, the flowmeter is used
to check the output of the pump. The flow meter can also
be used to find the location of leakage or restriction in
the system. Instructions for installation of the flow meter
and the use of the flowmeter are normally included with
the flowmeter.
3. Pressure Gauge - an instrument for measurement of
the pressure in the system. This indication is normally
given in pounds per square inch (psi) or bar. On this
machine, quick couplers are installed in the pressure
lines from the pumps. Pressure taken at these locations
will give an indication of operating pressure or relief
pressure.
Troubleshooting Procedures
For good troubleshooting, a step by step analysis of the
problem and the possible cause is necessary. First, find the
symptoms.
1. Check with the operator. Learn if there was a loss of
power (machine did not move the load) or a loss of
speed (slow cycle time).
2. Learn if the problem is common to all circuits or is found
in one or two circuits.
3. Make a visual inspection. Look for a restriction in the
linkages, low level of hydraulic oil, bent tubes, collapsed
or ballooned hoses, leakage around the hydraulic
components, etc.
Second, make an analysis of symptoms. The function of
each component in the system must be known before a
correct analysis can be made.
Remember:
1. If a problem is common to all circuits, the component
which is causing the problem must also be common to
all circuits. Examples are: the engine, pump, hydraulic
tank and filters.
2. If the problem is common to only two or three circuits,
the component which is causing the problem must be
common to those two or three circuits. Examples are:
pump section, relief valve, hydraulic swivel, etc.
3. If a problem is in only one circuit, then the component
which is causing the problem must be in that circuit.
Examples are: valve section, cylinder, motor.
Again, use the schematic. Find which components are in the
circuit or circuits. What component can cause the problem
with these symptoms? Make a list of the possible causes.
Start at the source of the flow in that circuit. If the problem is
in all circuits, start at the pump. Know the direction of oil flow
through each circuit.
Use the flowmeter and pressure gauge to check your
diagnosis of the problem. Start at the source of the flow and
check each component in sequence until the exact location
of the problem is found.
If the problem is two or three circuits, check each circuit
separately. After a circuit is checked, use caps or plugs to
remove that circuit from the system. Continue to next circuit
down the line until the problem is found.
Do not remove the main relief valve from the circuit. The
relief valve must be kept in the circuit to prevent damage to
the pump and other components.