Harwil^® type L-21N industrial level switches are low cost, high performance switches made from highly durable plastics. Commonly used on restoration tanks for carpet cleaners, they feature a variable liquid differential and a single point pump up/pump down level control. Interchangeable differential band modules, for all non L-21+ versions, allow for 5 minute on-site switching of differentials.
The L-21N comes in differential lengths and configurations.  Maintenance and checkout is a quick and seamless for plant maintenance personnel using any standard multimeter. Each unit comes with detailed instruction manual and parts list. Plastic test strips are available for testing in your particular real world chemical environment.