in this article, we clarify the difference between external and internal hydraulic leaks

External leak

External hydraulic fluid leakage is the most recognizable type of leakage. Even the untrained eye can easily spot a broken hose spewing oil like a Texas geyser. These types of leaks will typically be repaired quickly, because the equipment, production line or process will quickly come to a halt if the problem is ignored.

External leaks will results:

  1. in a loss of system pressure,
  2. loss of fluid,
  3. a rise in the temperature of the remaining fluid
  4. and cause a possible fire risk.

Internal leaks:

Internal planned leakage is typically small orifices or pathways that allow the hydraulic fluid from a higher pressurized zone of a system to travel into a lower pressurized zone to lubricate, clean and cool a specific component or area. These planned internal leaks do not allow the fluid to exit the hydraulic circuit, so there is no visual indication of its presence. The most common cause of excessive internal leakage is wear of component surfaces during normal operation.

The vast majority of hydraulic systems in operation today have leaks - leaks that are planned. They are designed with a specific function in mind, and in many cases, are documented by the original equipment manufacturer (OEM) as the amount of acceptable leakage under normal operating conditions.

Leakage can also result from poor system design, incorrect component selection, and poor quality control tolerances during the manufacturing of a component, and incorrect overhaul of rebuilt components.

System performance, reliability, and increased operating temperatures are the first visual signs of excessive internal leakage.

  1. happens from high pressure to low,
  2. causes a drop in system pressure,
  3. more activity of pressure regulating or cut-out valves
  4. and a rise in system temperature.
  5. Internal leaks cause a rise in fluid


Detection and quantification of the fluid consumption is the first step in external leak control. Up-to-date reservoir management records must be maintained to determine when by whom and how much fluid was required to top-up a reservoir. These records should be used along with visual inspections to determine the location and the leak rate of any detected anomalies.