1000529B Hengst Mechanical / Optical Maintenance Indicator (R901066232, WO-S01-2,2-V-10)1000529B Hengst Mechanical Optical Maintenance Indicator (R901066232, WO S01 2,2 V 10); 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 signals