1000525B Hengst Mechanical / Optical Maintenance Indicator (R901025312, WO-D01-2,2-M-160)1000525B Hengst Mechanical Optical Maintenance Indicator (R901025312, WO D01 2,2 M 160); Maintenance indicators facilitate the monitoring of filters by signaling when there is an excessive pressure differential and or back pressure in the filter. Features: Modular design; Mechanical visual indicators (WO) with a single switching point and memory function; Electronic switching element (WE) with one or two switching points; Capability to suppress