The Promass 83F from Endress + Hauser

The importance of relying on experienced professionals when installing instrumentation is greatly amplified when a project involves flowmeters. As the potential challenges posed by entrained air often leads to unsuccessful installations, end-users invariably end up wrongly blaming the instruments.

"Firstly, flowmeters are designed to operate in either gas or liquid flow, not both. All flowmeters give erroneous results when two phases flow together, unless additional expensive and complicated calculations are involved" explains Endress + Hauser Product Manager - Flow, Romeo Rocchetti, speaking out in an effort to increase awareness around the complexities of flowmeter design and installation. Flowmeters are designed and calibrated to operate in a single-phase fluid, with up to 50% deviations having been reported in horizontally installed applications.

"ISO 10790 regulations specify that it is important to establish the range of conditions to which a Coriolis meter will be subjected before identifying the optimum meter for a given application," he continues. "ISO guidelines further recommend that these conditions should include  for a pressure on the liquid adequate to prevent cavitation and flashing."

Flashing occurs when line pressure drops to, or below, the vapour pressure of the liquid. Cavitation, which is often caused by local dynamic pressure drops resulting from high fluid velocities, should be avoided at all cost, as it not only leads to inaccurate readings, but can easily damage the meter.