SECTION 2 - GENERAL
3121200
2-5
2.4
CYLINDER DRIFT
Theory
When a hydraulic cylinder is supporting a load, cylinder drift
may occur as a result of any of the circumstances below:
• Normal leakage of load holding valves or malfunction of
load holding valves. See Cylinder Leakage Test and
Table 2-2, Cylinder Drift below for evaluation.
• Damaged or worn piston seals.
• Normal thermal expansion or contraction of the hydraulic
oil within cylinders (See Cylinder Thermal Drift below).
The first two circumstances may result in cylinder movement
due to oil leaking out of the cylinder externally or by leaking
back to tank or due to oil leaking internally from one cylinder
chamber to the other.
Thermal expansion or contraction of oil in hydraulic cylinders
is a normal occurrence and does not result in oil leaking out of
the cylinder or leaking internally from one cylinder chamber
to the other. Thermal expansion or contraction is the tendency
for materials to change size in response to a change in temper-
ature.
Platform Drift
Measure the drift of the platform to the ground. Lower booms
(if equipped) slightly elevated, main boom fully extended with
the rated load in the platform and power off. Maximum allow-
able drift is 2 inches (5 cm) in 10 minutes. If the machine does
not pass this test, proceed with the following.
Cylinder Leakage Test
Cylinder oil must be at stabilized ambient temperature before
beginning this test.
Measure drift at cylinder rod with a calibrated dial indicator.
In an area free of obstructions, cylinder must have load
applied and appropriately positioned to detect drift.
Cylinder leakage is acceptable if it passes this test.
Cylinder Thermal Drift
The oil in all hydraulic cylinders will expand or contract due to
thermal effects over time and may result in changes to the
boom and or platform position while the machine is station-
ary. These effects occur as the cylinder oil changes tempera-
ture, usually from a higher oil temperature as it cools and
approaches the ambient air temperature. Results of these
effects are related to several factors including cylinder length
and change in temperature over the time the cylinder remains
stationary.
Table 2-2. Cylinder Drift
Cylinder Bore
Diameter
Max. Acceptable Drift
in 10 Minutes
inches
mm
inches
mm
3
76.2
0.026
0.66
3.5
89
0.019
0.48
4
101.6
0.015
0.38
5
127
0.009
0.22
6
152.4
0.006
0.15
7
177.8
0.005
0.13
8
203.2
0.0038
0.10
9
228.6
0.0030
0.08
NOTE:
This information is based on 6 drops per minute cylinder
leakage.
Summary of Contents for T500J
Page 1: ...Service and Maintenance Manual Model T500J PN 3121200 July 25 2018 Rev I AS NZS...
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Page 143: ...SECTION 3 CHASSIS TURNTABLE 3121200 3 107 Figure 3 45 Battery Charger Schematic...
Page 234: ...SECTION 5 BASIC HYDRAULIC INFORMATION SCHEMATICS 5 60 3121200 NOTES...
Page 246: ...SECTION 6 JLG CONTROL SYSTEM 6 12 3121200 Figure 6 5 System Test Flow Chart Platform Tests...
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