The cleanliness assessment challenge

It has been estimated that about 23% of the world’s total energy consumption is originated due to tribologic contacts.
Of that, about 20% is used to overcome friction and 3% is directly used to remanufacture worn parts and related spare equipment. Definitely, this is a lot.

Most of the problems encountered in hydraulic equipment, as well as in automotive and aeronautic systems through which a fluid flows, are directly related with contamination formed by solid particles (metals, powder, rubber, fibres, etc.). The damage caused by these particles during the first minutes of operation determine the reliability and life expectancy of the component.

The development of internal wear is accelerated due to the abrasion and fatigue suffered by components subjected to relative motion.
The origin of this contamination in hydraulic systems can be diverse, but it usually comes from the manufacturing processes (machining, grinding, welding, etc.) or the subsequent assembly operations to produce subsystems or end-products. Sometimes it can even come from the hydraulic fluid.

The real data regarding the problem

These real data, obtained from a small excavator, illustrate the problem.

When the new excavator starts running, at 300 bar the hydraulic pump supplies a maximum flow of 55 l/min and generates a maximum power of 29.6 KW/h., for a theoretical yield of 0.96. If the hydraulic components haven’t been properly cleaned and no fluxing of the circuit has been done during start-up, the performance of the excavator falls really quickly.

After only 7 hours working, the maximum flow at 300 bar has dropped to 45 l/min and the maximum power is only 24.2 KW/h, for a yield of 0.79. This 5.4 KW/h lost in practice means less precision, lower working speeds and higher fuel consumption (1 KW/h of power lost is equivalent to approximately 0.3 l/h more of fuel consumption). Thus, the energy losses in a big machine due to contamination can become really important (beware that many hydraulic machinery and systems work intensively or even non-stop).

Small size excavator Pump just installed After 4 hours of work After 7 hours of work
Pressure (max.) 300 bar 300 bar 300 bar
Flow (max.) 55 l/min 55 l/min 45 l/min
Power (max.) 29.6 KW/h 27.4 KW/h 24.2 KW/h
µ (theoretical) 0.96 0.89 0.78

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