LIQUID VISUAL DISPLAY

摘要

A display provides indicates the remaining useful life of a filter element by providing a visible level of fluid in the display corresponding to the remaining useful life. The fluid level is adjusted by a valve responsive to a pressure differential across the filter element. An increasing pressure differential produces an increased fluid level in the display. The display may be provided with markings indicating that a particular fluid level in the display corresponds to the need to change a filter cartridge containing the filter element.