Terex T780 - Temperature Effects on Telescope and Boom Hoist Cylinders

Temperature Effects on Telescope and Boom Hoist Cylinders
Background
Liquids exhibit changes in volume with changes in temperature. The degree of volume
expansion divided by the change in temperature is called the material's coefficient of
thermal expansion and generally varies with temperature. The thermal expansion coefficient
of Petroleum oils varies slightly depending on several factors including API Specific Gravity.
Generally, lower API oils expand at a higher rate than those with a higher API classification.
The differences however are minimal and may be neglected for the purpose of this
discussion. This thermal expansion characteristic leads to cylinder retraction as the
hydraulic oil within the cylinder cools. This causes what is commonly referred to as “Load
Drift” in hydraulic telescoping boom cranes. It is exhibited by all hydraulic telescoping
boom cranes to varying degrees.
Load drift occurs when the hydraulic cylinder holding the load changes length over time.
The change in length of the cylinder is proportional to its extended length and the oil
temperature change within the cylinder. The rate at which the oil in a cylinder cools is
dependent upon several factors. These factors include the differential temperature between
the oil and ambient, thermal mass of the cylinder body and rod, and volume of oil to name
a few. Assuming no internal leakage, load drift progresses until such time (given sufficient
time) that the oil temperature in the cylinder reaches ambient temperature.
Safe crane operation involves careful monitoring of numerous environmental, jobsite, and
equipment conditions, including an awareness of the load drift phenomenon. As the
telescope and boom hoist cylinders retract, the load may radius increase and the load
height decreases. This can increase the risk of tipping when handling loads close to the
stability limits of the crane. The opposite situation occurs when cold oil is heated by
ambient temperatures. In this case the cylinders will extend, increasing boom length and
boom angle, possibly increasing radius.
Load Drift Graphs
The graphs below provide guidance to understand the expected load drift behavior of the
RT130 crane based on hydraulic oil temperature changes for various boom lengths and
parts of line.
T300-1_T500-1_T780
Safety
60 P/N 12261-683
REVISED: January 2015