Usually used with a return pump, this Neptune Systems FS-200 Flow Sensor - 2" w/ Unions can be placed in line with the flow on any pipe, connected to the Neptune Systems FMM, and communicate to your Apex the flow rate of water through that pipe. The flow sensor itself uses British Standard Parallel Pipe (BSPP) threads so for North American customers we have included two specially designed PVC unions with slip fittings to adapt it to standard 2″ PVC plumbing. The FS-200 will work with flow rates from 300-3000 gph.