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Temperature shock in hydraulic motors ben lee

Temperature is an important variable in many aspects of hydraulic motor operation.  The operating temperature of the machinery informs the type of hydraulic oil used in the system, as it must be able to withstand certain temperatures without degrading or becoming too thin, both of which cause damage to internal components.  The ambient temperature in which the machinery is located also informs this decision, as machinery that operates at low temperatures will require a certain type of oil, that remains at the right viscosity even when cold.  Similarly, a high ambient temperature requires a hydraulic fluid that is capable of remaining thick enough even at these temperatures.  Factoring in the increase in heat that comes from the operation of the motor should also inform the type of hydraulic fluid that is used.

 

Temperature shock in a hydraulic system is when the fluid in one part of the system has reached peak operating temperature and is then allowed to flow into an idle part of the system.  In this idle part the components are cold, and expand when they come into contact with the hot fluid.  The tiny spaces between moving parts are compromised and in some cases closed entirely due to the expansion of the metal and this causes seizing, erosion of the components and serious damage to the moving parts.

 

Temperature shock is a big issue for hydraulic systems which operate in stages, such as diving winches, where two motors are used to drive two winches, one which lowers equipment and another which brings it back to the surface.  To start with the lowering motor is in operation, which raises the temperature of the oil inside the system.  When the returning motor is initiated it is cold, but the fluid entering it has already been heated by the first motor.  If you are finding that the same components in the second stage of the system are frequently wearing out or breaking and there is no other plausible reason for this, (such as incorrect maintenance, contaminated or incorrect fluid) then temperature shock is the most likely culprit.  It causes expensive repairs and a huge amount of downtime that can be avoided with a simple measure.

 

The best solution to reducing and eliminating temperature shock is to continuously flush the motor case during operation.  Only a small amount of hydraulic fluid needs to be flushed through the system, as it is not there for operation but to maintain a constant temperature.  By keeping a constant temperature through all parts of the motor system, the components have time to adjust to the increase in temperature, rather than quickly expanding and seizing, causing breakages of vital components. 

 

The flushing system does not have to drain any oil as part of this process, as the flushing itself is not intended to clear the system but to circulate fluid at a constant temperature throughout the system.  A flushing valve installed between the pump, where most heat is generated and transferred to the fluid, and the motor case is a simple way of achieving the correct circulation.  It is also possible, with some clever engineering, to adapt an existing case flushing and draining system to function as solely a case flushing system when needed, but this should be carried out by an experienced hydraulic engineer with experience of rebuilding systems.




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