Flowmeters still going strong a decade on

Two Litre Meter VFF rotary piston flowmeters recently returned after ten years for checking and recalibration were found to have minimal wear, even after a decade of extreme continuous production use

Stretch wrap film manufacturer Total Polyfilm sent back two of the 17 Litre Meter VFF mass flow meters it uses in its manufacturing process because they had been operating for ten years and were overdue for service.

Litre Meter VFF rotary piston flow meters are designed to work under the harshest conditions, and these units had been in continual use 24 hours a day, seven days a week for 51 weeks of the year.

As part of the Total Polyfilm manufacturing process the flowmeters have to be able to withstand high temperatures.

The main ingredient in the film is polyisobutene (PIB).

The chemical is very viscous at low temperatures.

Even at temperatures of 80 or 90 degrees Celsius it still has a high viscosity and its flow through the meter places a lot of demand on the rotor.

The flowmeters control the amount of PIB that goes into the product mix.

The instruments are calibrated in kilograms per hour and they operate up to a maximum of 20kg/hr.

Weight is used because the final product is measured in weight.

The final output of the product is known - 250kg/hr.

The amount of PIB going into the mix is calculated as a percentage of the final output.

Not only are the flowmeters operating continually at high temperatures they work continually with thick materials in a dusty environment.

Paul Lockett, procurement manager at Total Polyfilm, said: "We have only now, after ten years, sent two of the meters back for checking: they will be returned to use after recalibration despite being operated at levels of use and wear well above what they were originally designed for".

Each meter has a rotor within a measuring chamber which rotates as the material flows through it, giving an output representing an increment of volume flow.

The rotor is basically a disc shape with a circular cavity on its underside which can hold and transport flow from the chamber inlet to the outlet.

The rotary piston design modifies the rotation to an oscillation.

The top of the rotor is equipped with a rare earth magnet that activates a reed-switch sensor.

A volt-free contact closure output signal is therefore given for each oscillation which represents a specific volume.

The typical metering repeatability is better than 0.2 per cent with a meter accuracy of 1.0 per cent.

Steve Smith, applications engineer at Litre Meter, said: "When we tested the meters from Total Polyfilm on our calibration rig it was discovered that the meters were still in full operating condition, requiring minimal repairs or alterations.

With only one moving part, there is very little to go wrong with them and they are now going back into service.

This is a fine example of the robustness and reliability of Litre Meter VFF rotary piston flowmeters".

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