How to Select a Flow Meter for Water and Wastewater Applications

Raw Water and Potable Water

Raw-water and potable-water lines are often strong magnetic-flow applications when conductivity is adequate. Large transmission lines can favor AXW because the family extends to very large diameters, while plant-level or smaller process connections may fall into either AXG or AXW depending on size and project specification. Important inputs include min/normal/max flow, seasonal demand, pressure class, whether the meter may be submerged, required drinking-water approvals, and the available straight-run and installation arrangement. Where a meter is replacing an older magnetic flowmeter, flange dimensions, converter arrangement and existing cabling should be included in the review.

Wastewater, Sewage and Treated Effluent

Wastewater and sewage frequently contain suspended solids, making a full-bore electromagnetic meter attractive where the liquid is conductive and the selected materials are appropriate. AXW is explicitly positioned by Yokogawa for sewage and drainage applications. The selection should still consider solids size and concentration, grease or coating tendency, abrasion, chemical cleaning and whether the meter is installed in a wet well, buried chamber or other environment that affects enclosure or submersible requirements. For treated effluent, the fluid may be cleaner but conductivity can become more important if treatment significantly reduces dissolved ions.

Sludge and Solids-Bearing Streams

Sludge is not one uniform fluid. Primary sludge, activated sludge, digested sludge and dewatered sludge can have very different solids content, rheology and coating behavior. Magnetic flow measurement is often considered because the meter has no moving obstruction in the bore, but the application must be checked for conductivity, abrasion, adhesion and whether the pipe remains completely full. Very difficult high-solids or strongly adhesive media should be treated as a dedicated application-engineering problem rather than an automatic AXG or AXW selection.

Desalination and High-Salinity Water

Desalination plants include seawater intake, pretreatment, reverse-osmosis feed, permeate, brine, remineralization and chemical-dosing services. Magnetic flowmeters can be relevant to many conductive liquid streams, but salinity and chemical composition make wetted-material selection important. The process description should therefore specify the stage of the plant, chloride level or chemical composition where relevant, pressure and temperature, rather than using the broad term ‘desalination water’. High-pressure RO feed may also have different pressure-class requirements from conventional treatment lines.

Chemical Dosing: When Coriolis May Be More Appropriate

A small chemical-dosing line can have a different objective from a large water-transfer line. If the process requires direct mass flow, density or highly accurate batch quantities, ROTAMASS Coriolis may be a better starting point than a magnetic meter, provided the chemical, flow range and pressure-drop requirements suit the technology. Magnetic flow can still be appropriate for conductive dosing chemicals, especially where the process favors a full-bore design. The selection should be made from the dosing objective rather than from line size alone.

Cooling Water and Plant Utilities

Cooling-water circuits are normally conductive-liquid applications and can be strong candidates for magnetic measurement. However, water-treatment plants also use steam, compressed air and gases as utilities. Those services should not be pushed into the magnetic-flow category. Yokogawa vortex flowmeters can measure suitable liquids, gases, saturated steam and superheated steam and are therefore relevant to utility systems outside the main water stream. The Magnetic vs Coriolis vs Vortex Flow Meter comparison can help separate these technology choices before product sizing begins.