FLOW METERS

Flow meters are used to measure the flow rate of a liquid or gas flowing inside a pipeline. They can also be transmitters if they have an output signal.

They are available in several different types and the choice shall be made based on

• Required measurement range
• Process design conditions
• Type of fluid: liquid or gas, density, viscosity, pressure and temperature fixed or constant
• Pipe size
• Connections size and type
• Direction of flow
• Required accuracy

The different types are divided according to the measurement principle and they are:

• Variable Area: a float is placed inside a conical tube. As the flow increases, the float rises to a higher position in order to increase the flow passage area
• Differential Pressure: they create a pressure difference inside the line. This pressure difference is proportional to the fluid’s flow rate. They are divided according to the element that generates the pressure drop.
  • Orifice plate: a diaphragm narrows the pipeline’s diameter. Available as the orifice plate only; the orifice plate coupled with a pair of flanges with pressure taps: “Orifice Plate Assembly”; or a fully assembled pipe section: “Meter Run”.
  • Nozzle: they narrow the pipeline with a well-blended profile to allow the measurement of higher flow rates, for the same size. The profile is also more suitable for abrasive fluids such as steam.
  • Venturi: consists of a short straight tube connected at the ends to two conical tubes.
  • Conical Venturi: a cone placed inside a straight pipe.
  • Wedge: a wedge placed inside a straight pipe.
  • Pitot tubes: a tube placed inside the pipeline with the opening facing upstream. They can be made in the “Multiport Averaging” version that consists of a tube with various openings inserted perpendicular to the flow’s direction.
• Velocity: they measure the flow velocity and they are divided into
  • Elecromagnetic: they measure the velocity of conductive fluids by applying a magnetic field perpendicular to the flow direction and measuring the electromotive force generated.
  • Turbine: they consist of a straight pipe section with a rotor inside driven by the flow. The rotational speed is detected through a magnetic pick-up and is proportional to the flow velocity.
  • Ultrasound: there are two types, Transit Time or Doppler. The first one consists of two transducers that measure the time difference with which sound propagates in the pipe between the case in which the sound travels in the direction of flow and the case in which the sound travels upstream. The Doppler Effect ones are used if the fluid contains particles or bubbles capable of reflecting the sound, and they work by emitting a sound wave in the flow’s direction and measuring the frequency of the returning signal. The difference in frequency between the outgoing and returning wave is directly proportional to the fluid velocity.
  • Vortex: they consist of a straight pipe section with an obstruction inside that generates vortices. The frequency of vortex formation is directly proportional to the flow rate of the fluid.
• Mass
  • Thermal mass: they measure the heat loss of a heated element, that is directly proportional to the fluid’s flow rate.
  • Coriolis: the flow is divided into two tubes that are free to oscillate. The movement of one tube relative to the other is measured at the inlet and outlet by magnetic pick-ups. The difference in oscillation between the inlet and the outlet is proportional to the flow rate.
• Volumetric or positive displacement: they mechanically divide the fluid into known volumes and count how many of these volumes pass through the instrument.

Discover Officine Orobiche Variable Area Flowmeters: https://www.officineorobiche.it/en/categoria-prodotto/variable-area-flowmeters/

Discover Officine Orobiche Flow Elements: https://www.officineorobiche.it/en/categoria-prodotto/flow-elements/