Hydraulic Efficiency (Volumetric / Overall Efficiency)
It is the measure expressing how well a pump or motor works, through two separate ratios. Volumetric efficiency is the ratio of actual flow rate to theoretical flow rate and is typically above 90 percent on new pumps; overall efficiency also includes mechanical losses and generally falls in the 80-90 percent range.
Volumetric efficiency is the measure of internal leakage. Oil escaping through the clearances inside the pump from the pressure side to the suction side is lost without ever leaving the pump. As wear increases, this leakage grows.
- Diagnostic method: outlet flow rate is measured at a fixed speed and compared with the theoretical value calculated from the pump's displacement and speed.
- Volumetric efficiency is above 90 percent when new and drops over time; when it has noticeably declined the machine slows down under load but looks normal at idle.
- Leakage increases in hot oil; that is why the performance loss is more pronounced on a warmed up machine.
The most familiar field symptom is this: the machine runs well in the morning, gets sluggish as it warms up, and slows down visibly while lifting a load. Whatever you do on the controller or remote control side, you cannot fix this picture; measurements must be taken and the pump evaluated. Verifying the health of the hydraulic side before starting electronic improvements saves time.
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