Purge Type Tank Level Indicator model no. : fitzer / pli / 800 fitzerpurge type level indicator is simple reliable for direct reading in atmospheric or pressurised tank application it is compressed air operated and functions under the same basic principles of the u-tube manometer whose accuracy is inherent. Indicator is recommended where continuoues indication of level of liquid in a tank is required by compressed air or build in hand pump which is operated only when an indicator reading is desired.