Neptune Systems Apex Flow Sensor - 1″ (FS-100)Neptune Systems Apex Flow Sensor 1 (FS 100) Usually used with a return pump, this flow sensor can be placed in line with the flow on any pipe, connected to the FMM, and communicate to your Apex the flow rate of water through that pipe. The flow sensor itself uses BSPP threads so for North American customers we have included two specially designed PVC unions with slip fittings to adapt it to standard 1 PVC plumbing. The FS 100 will work with flow rates