Metal-Tube Variable Area Flowmeter

A variable area flowmeter, or rotameter, is a tapered tube with a float inside. Flow lifts the float until the annular gap around it passes the flow at equilibrium, and the float position indicates the rate. It needs no power and no straight pipe runs, and it shows the flow directly on a local scale. The metal-tube version replaces the glass with a stainless steel tube and transmits the float position to the indicator through a magnetic coupling, so the meter can be used at high pressure and temperature and on opaque, corrosive or hazardous fluids.

Meters are available from ½" to 4" with flanged, threaded, DIN hygienic or Tri-Clamp connections, for flows from 1 to 100,000 L/h, pressures to 100 bar and temperatures from −196 to +400 °C or higher on request. Wetted parts are 316 / 316L stainless steel, Hastelloy, Monel 400, Inconel 600, Incoloy 825, super-austenitic stainless steel or titanium.

The standard output is the mechanical pointer; an electrical transmitter adds 4–20 mA, HART, fieldbus or PROFIBUS, and inductive switches give minimum and maximum flow alarms. Options include inlet and outlet valves, a self-regulator for constant flow, a dampener for pulsating flow, insulation and heat tracing, panel mounting and coatings.

Metal-tube rotameters are used for viscous and corrosive liquids and gases in oil and gas, chemical, petrochemical, power and water treatment, particularly for seal, purge and cooling flows and chemical dosing where a visible local reading matters.