An inexpensive switch for use with compatible liquids to start or stop electronic operated equipment when flow or no-flow conditions occur. Magnetic operation is simple and dependable with no mechanical linkages or seals to wear or leak. Lower body is machined solid metal bar stock assuring no leak points, no matter how long the unit is in service. Design is standard weatherproof, meeting NEMA 4X (IP66), for application versatility. Robust vane design is rigid and field trimmable for set point adjustment.