1009242B Hengst Mechanical / Optical Maintenance Indicator (R928038785, WO-D01-8,0-M-450)1009242B Hengst Mechanical Optical Maintenance Indicator (R928038785, WO D01 8,0 M 450); 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