Which Flowmeter to Choose for Vane Pump Operations?

Related Vendors

Lutz Pumpen GmbH

Maag Pump Systems AG

Anton Paar GmbH

Blackmer

To determine the accuracy and effectiveness of Coriolis meters with positive-displacement pumps, pump manufacturer Blackmer undertook a study, the results of which have been published in a white paper (see PROCESS-Tip).

Why Choose Mass?

Coriolis flowmeters offer users several advantages over PD meters:

• Liquids in a Coriolis flowmeter pass only through smooth tubes with no moving parts, so there is no mechanical wear of the measuring elements. There are also no parts subject to abrasion, erosion or corrosion.

• Particulates nearly as large as the measuring tube diameter can pass through the meter without constraint.

• Coriolis meters are not affected by temperature or pressure. They measure mass flow directly, which does not change even if the temperature or pressure of the fluid changes. Therefore, no pressure or temperature compensation is required.

• Accuracy is typically listed as ±0.1–0.2 percent of the flowrate being measured. This is much more accurate than mechanical meters, which are listed as being within ±0.5 percent of full-scale flow. Other types of meters also need pressure and temperature compensation, and the additional error in these measurements can increase the overall flow error to as much as ±3 percent.

• Because of their high precision, Coriolis flowmeters have a turndown ratio of about 100:1 or more. This means that if a meter is rated for a maximum flowrate of 200 gpm, it is still accurate down to 2 gpm. Typical me-chanical meters have a turndown ratio of 10:1.

• There is minimal pressure drop through a Coriolis mass flowmeter with lower-viscosity fluids. The only pressure losses are caused by the splitting of the flow into the two measuring tubes. Orifice plates, flow nozzles, venturi tubes and PD meters, in contrast, all have sig-nificant pressure losses.

• Coriolis meters are unaffected by changes in viscosity during a process or batch run. Orifice plates and the other differential-pressure meters need to be calibrated for various viscosities, and the viscosity needs to be measured during operation to ensure accurate metering.

Some disadvantages have also been reported. Pressure drop can increase significantly in higher-viscosity fluids; Coriolis meters take up more space than PD meters, although this may be offset by a reduction in the amount of straight pipe needed to straighten the flow; and they are more expensive.

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