Hengst's WE and WO maintenance indicators monitor filters, alerting to pressure differences or accumulated pressure. They offer a modular structure, mechanical-optical (WO) indicators with memory function, and electronic (WE) indicators with up to two switching points. They support signal suppression during cold starts, and offer a more robust stainless steel option. They are applicable to pressure line (WO) and return line (WO) filters, as well as electronic pressure switches (WE). They operate between -30°C and +100°C (WO) or up to +85°C (WE), with nominal pressures from 10 to 450 bar.