What is a sign of proper functioning in hydraulic pumps related to leakage?

In hydraulic systems, a sign of proper functioning in hydraulic pumps is that they maintain a small percentage of internal leakage. A range of 5-15% internal leakage is generally acceptable as it indicates that the pump is operating effectively under its design parameters. This small amount of leakage is often necessary to lubricate the internal components and ensure that the pump functions smoothly.

Excessive internal leakage beyond this threshold could suggest wear and tear or damage within the pump, which can significantly impact its efficiency and performance. Conversely, having no internal leakage is ideal but can be unrealistic in practical applications since some small level of leakage is typical due to the mechanical tolerances and clearances within the pump design. External leakage is problematic as it can lead to loss of hydraulic fluid and potential safety hazards, making the option of leaking externally but not internally less favorable. Therefore, the maintenance of 5-15% internal leakage is seen as a sign of a healthy hydraulic pump.