TM 5-3805-258-24-1
H Y D R A U L I C
S Y S T E M
T E S T I N G
A N D
A D J U S T I N G
Cycle times in the lift and tilt circuits: Cycle
times that are longer than those shown are the
result of leakage, pump wear and/or pump speed
(rpm).
If the basic tests give an indication of circuit leak-
age, install a Flow Meter and do a system test. This
procedure will find the source of the leakage.
Relief valves in the tilt circuits give protection to
the components from pressures in the circuits when
the tilt control valve is in the HOLD position.
VISUAL CHECKS
A visual inspection of the hydraulic system and its
components is the first step when a diagnosis of a
problem is made. Stop the engine, lower the bucket to
the ground. To remove the tank filler cap, slowly turn
the filler cap until it is loose. If oil comes out the bleed
hole, let the tank pressure lower before the filler cap
is removed. Make the following inspections:
1.
2.
3.
4.
5.
Measure the oil level.
Look for air in the oil that is in the tank. Do this
immediately after the machine is stopped. Use a
clear bottle or container to get a sample of the
oil. Look for air bubbles in the oil that is in the
bottle.
Remove the filter elements and look for particles
removed from the oil by the filter elements. A
magnet will separate ferrous particles from non-
ferrous particles (piston rings, O-ring seals,
etc.).
Inspect all oil lines and connections for damage
or leaks.
Inspect control linkage for bent, broken or dam-
aged components.
PUMP EFFICIENCY CHECK
For any pump test, the pump flow, measured in
liter/rein (U.S. gpm) at 690 kPa (100 psi) will be
larger than the pump flow at 6900 kPa (1000 psi) at
the same rpm.
The difference between the pump flow of two oper-
ating pressures is the flow loss.
Method of finding flow loss
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pump flow at 100 psi . . . . . . . . 57.5 gpm (liter/min)*
Pump flow at 1000 psi . . - 52.0 gpm (liter/min)*
Flow loss
5.5 gpm (liter/min)*
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flow loss when expressed
flow is used as a measure of
as a percent of pump
pump performance.
Example of finding percent of flow loss . . . . . . . . . . . . . . . . .
Percent
gpm flow loss
X 100 = of flow
Pump flow @ 100 psi
loss
*15.5
or
X 100 = 9.5%
*57.5
If the percent of flow loss is more than 10%, pump
performance is not good enough.
*Numbers in examples are for illustration and are
not values for any specific pump or pump condi-
tion. See SPECIFICATIONS FOR 950B WHEEL
LOADER HYDRAULIC SYSTEM, Section 2, for
pump flow of a new pump at 100 psi and 1000 psi.
Test On The Machine
Install a Flow Meter. Run the engine at high idle.
Measure the pump flow at 100 psi (690 kPa) and at
1000 psi (6900 kPa). Use these values in Formula I.
Formula I
Percent
gpm @ 100 psi - gpm @ 1000 psi
X 100 = of flow
gpm @ 100 psi
loss
Test On The Bench
If the test bench can be run at 1000 psi and at full
pump rpm, find the percent of flow loss using For-
mula I.
If the test bench can not be run at 1000 psi at full
pump rpm, run the pump shaft at 1000 rpm. Mea-
sure the pump flow at 100 psi (690 kPa) and at 1000
psi (6900 kPa). Use these values in the top part of
Formula II. For the bottom part of the formula, run
the pump shaft at 2000 rpm. Measure the pump flow
at 100 psi.
Formula II:
Percent
gpm @ 100 psi - gpm @ 1000 psi
X 100 = of flow
Pump flow @ 100 psi @ 2000 rpm
loss
OPERATION CHECKS
The operation checks can be used to find leakage
in the system. They can also be used to find a bad
valve or pump. The speed of rod movement when the
cylinders move can be used to check the condition of
the cylinders and the pump.
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