1000531B Hengst Mechanical / Optical Maintenance Indicator (R901066235, WO-D01-5,0-V-450)1000531B Hengst Mechanical Optical Maintenance Indicator (R901066235, WO D01 5,0 V 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