Grove Published 4-09-2021, Control # 364-11 2-41
RT765E-2 OPERATOR MANUAL SAFETY INFORMATION
TEMPERATURE EFFECTS ON HYDRAULIC
CYLINDERS
Hydraulic oil expands when heated and contracts when
cooled. This is a natural phenomena that happens to all
liquids. The coefficient of expansion for API Group 1
hydraulic oil is approximately 0.00077 cm³ per cm³ of volume
for 1°C of temperature change (0.00043 in³ per in³ of volume
for 1°F of temperature change). Thermal contraction will
allow a cylinder to retract as the hydraulic fluid which is
trapped in the cylinder cools.
The change in the length of a cylinder is proportional to the
extended length of the cylinder and to the change in
temperature of the oil in the cylinder. For example, a cylinder
extended 7.6 m (25 ft) in which the oil cools 15.5°C (60°F)
would retract approximately 196 mm (7 3/4 in) [see Table 2-9
and Table 2-8]. The rate at which the oil cools depends on
many factors and will be more noticeable with a larger
difference in oil temperature verses the ambient
temperature.
Thermal contraction coupled with improper lubrication or
improper wear pad adjustments may, under certain
conditions, cause a “stick-slip” condition in the boom. This
“stick-slip” condition could result in the load not moving
smoothly. Proper boom lubrication and wear pad adjustment
is important to permit the boom sections to slide freely. Slow
movement of the boom may be undetected by the operator
unless a load is suspended for a long period of time. To
minimize the effects of thermal contraction or “Stick-slip” it is
recommended that the telescope control lever is activated
periodically in the extend position to mitigate the effects of
cooling oil.
If a load and the boom is allowed to remain stationary for a
period of time and the ambient temperature is cooler than the
trapped oil temperature, the trapped oil in the cylinders will
cool. The load will lower as the telescope cylinder(s) retracts
allowing the boom to come in. Also, the boom angle will
decrease as the lift cylinder(s) retracts causing an increase
in radius and a decrease in load height.
This situation will also occur in reverse. If a crane is set up in
the morning with cool oil and the daytime ambient
temperature heats the oil, the cylinders will extend in similar
proportions.
(Table 2-8) and (Table 2-9) have been prepared to assist you
in determining the approximate amount of retraction/
extension that may be expected from a hydraulic cylinder as
a result of change in the temperature of the hydraulic oil
inside the cylinder. The chart is for dry rod cylinders. If the
cylinder rod is filled with hydraulic oil, the contraction rate is
somewhat greater.
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