26 March, 2010-
Meaning: At
times, when the temperature of a
hydraulic component is
reasonably different from the fluid supplied, it most often leads to the
localized heating of internal parts of the hydraulic component. This in
turn, results into the expansion of individual parts of the component at
varied rates which hampers the smooth functioning of system. This entire
problem is termed as Temperature shock. Temperature shock prompts
intervention between hydraulic parts that normally has smooth
clearances.
Temperature shock takes place when a certain part of hydraulic circuit
is continuously operated for so long that it leads the the hydraulic
fluid in the system to reach the operating temperature. At this point,
an idle part of the circuit is put to function which ultimately results
in the transfer of hot fluids to cold components.
Example: The concept of temperature shock can be understood more
transparently with the help of an example citing diving bell launch and
a recovery system which comprises of a hydraulic power unit, a bell
winch, an umbilical winch and a guide-wire winch.
Suppose, to launch the bell, a clump weight to the seabed is lowered
using a guide-wire winch(guide wire holds back the bell from spinning
during launch and recovery). Thereafter, the bell and its umbilical are
launched using their respective winches.
Once the divers are done with their shift of 6-8 hours on the seabed,
the bell and its umbilical are recovered, followed by the clump weight.
Now, the problem here is that when the winch is summoned to haul up the
clump weight, the distributor shear pin is frequently sheared leading
the winch non-serviceable.
Here, the hydraulic system was at an atmospheric temperature at the
start of recovery operation but, by the time the bell and its umbilical
had been hauled up, the hydraulic fluid had reached operating
temperature. Since the guide-wire winch was still maintained at
atmospheric temperature, it lead to the hot fluid enter the cold motor
during clump weight recovery. It eventually lead to the expansion and
contraction of distributor valve within its shell rendering in the
failure of shear pin and consequently, the motor non-serviceable.
Solution: The simple solution to prevent temperature shock of
hydraulic motors is to flush the
motor case i.e. circulate a relatively small amount of fluid through the
case, on regular intervals. This would help maintain a common
temperature amongst the fluid and the system.
