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Properly Installing Liquid Magnetic Flowmeters

·3 mins
Valve Process Control Utilities
Table of Contents

If you ever face the problem of jittery process values from magnetic flowmeters, read on to learn how to solve the issue.

Mag FT unstable output

Fluid Properties #

  1. High Flow Noise: When used for fluids with high flow noise (pure water, low viscosity and low conductivity fluid such as alcohols), the output fluctuation increases and the measurement is affected. In these cases, a Vortex flowmeter or Coriolis flowmeter is recommended.
  2. Abrasive Slurries: For abrasive slurry fluids mixed with minerals, earth, and sand, install the meter on vertical piping. This reduces uneven wear of the lining.
  3. Permeable Fluids: For use with permeable fluids (e.g., nitric acid, hydrofluoric acid, high-temperature sodium hydroxide, etc.), select a model with PFA lining, a vent hole, and a thick type grounding ring plate.
  4. Chemical Injection: If chemicals are fed near the upstream side of a magnetic flowmeter, they may affect the flow-rate’s indications because of unstable fluid conductivity. It is recommended that chemical feed ports be located on the downstream side. If upstream feeding is unavoidable, provide a sufficient straight pipe length of approximately \(50D\) or more to ensure proper mixture.

Grounding #

Grounding is unnecessary for metal piping that has no lining. In that case, connect the piping and the sensor flange part with a grounding wire supplied by the customer. However, be sure to select a grounding device when installed in plastic or lined piping. For high-pressure types (ASME Class 600 flange), use a flat gasket that matches the outer and inner diameters of the grounding ring, considering the seal structure dimensions of the flange.

Noise Avoidance #

The flowmeter should be installed away from electrical motors, transformers, and other power sources to avoid measurement interference. When installing two or more magnetic flowmeters, provide a distance of at least \(5D\) (where \(D\) is the FT’s connection port size) from each other.

Important Aspects: #

  • A straight run may not be required on the downstream side; however, if a downstream valve or fitting causes flow irregularity, provide a distance of \(2D\) to \(3D\).
  • Valves should be mounted on the downstream side so that deviated flows do not occur in the sensor and to avoid startup from an empty condition.
  • If piping conditions are compounded, install on a straight pipe section where the upstream part is sufficiently rectified.

Mounting Positions #

Vertical mounting is effective when fluids tend to separate or solid matter may precipitate. When employing vertical mounting, direct the fluids from the bottom to the top to ensure the pipes remain fully filled.

In cases where fluids contain air bubbles, the piping must be designed to prevent bubbles from accumulating in the measurement pipe. If a valve exists near the sensor, try to mount the sensor on the valve’s upstream side to prevent pressure reduction and the resulting air bubbles.

Mounting Orientation #

Install the magnetic flowmeter so that the electrode position is not perpendicular to the ground. Otherwise, air bubbles at the top or slurry at the bottom may cover the electrode and cause measuring errors. Mount the terminal box of a remote sensor and the transmitter of an integral flowmeter above the piping to prevent water ingress.