If a low conductive fluid flows through a conventional hydraulic or lubricating oil filter element, the liquid can get highly charged due to charge separation effects. When exceeding a certain limit, the charge can suddenly be balanced by electrostatic discharges. These discharges can occur in different ways and at different points. The most obvious form is a spark discharge outside the system or in the tank. Discharges within the filter element can usually be heard by cracking noises (similar to cavitation).