Flow sensor selection is driven by the media, line size, flow range, accuracy requirement, and the installation context (full-pipe vs. partial, straight-run upstream and downstream). The wrong technology for the media — for example, magnetic flow on a non-conductive fluid — simply will not produce a useful signal.
Specs to confirm before ordering:
- Media: water, oil, glycol, slurry, air, natural gas, steam
- Technology: thermal mass (gas, low flow), vortex (steam, gas, clean liquid), paddle wheel (water-like fluids), electromagnetic (conductive liquids only), ultrasonic (clean fluids, clamp-on options), turbine (clean low-viscosity liquids)
- Pipe size and process connection (threaded, flanged, sanitary clamp, insertion-style)
- Flow range — units of GPM, L/min, Nm³/h, SCFM as appropriate, with turndown ratio noted
- Output: switch only, analog 4–20 mA, pulse for totalizer, IO-Link, fieldbus
- Required straight-run pipe upstream/downstream (often 10D upstream, 5D downstream)
- Process temperature and pressure
- Wetted materials compatible with the media
- Hazardous-area certification if needed (Class I Div 2, ATEX, IECEx)
Common gotchas: electromagnetic meters require a conductive fluid (minimum ~5 µS/cm) — they do not work on hydraulic oil or DI water. Paddle wheels are inexpensive but wear out on dirty or fibrous media. Vortex meters need stable, fully developed flow — installing one immediately after a 90° elbow gives unstable readings. Thermal mass air-flow sensors are sensitive to mounting orientation and to changes in gas composition.
Typical applications: compressed-air consumption monitoring in plant utilities, cooling-water flow verification on welding equipment and induction heaters, batch totalizing in chemical mixing, and lubrication-flow confirmation on rolling mills. On legacy machines, a discontinued OEM flow switch or transmitter is usually best replaced in kind — the original was sized with the pipe geometry in mind, and switching technology can require re-piping.
For obsolete flow sensors, request a quote with the OEM number.
