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Sensors
EUROMAG | SENSORS | Ed. 04/2019
3.5
HOW TO AVOID AIR POCKETS IN THE PIPELINES
This paragraph is intended to help the designers and users of electromagnetic flowmeters to create
the best installation layout that guarantees optimum performance of the meter, taking into particular
consideration the problem of the presence of air pockets in the pipe.
Fig. 36
Pumping stations with flowmeters and vent valves
What are the problems caused by the air pockets entrapped in any flowmeter?
The presence of air pockets can cause serious reading errors or strong instability. In this case, the
flowmeter could go into Error mode (see the related converter manual).
How are air pockets removed, or moved away from the flowmeter?
The air pocket inside a pipe always moves toward the top of the pipe, and it is assumed that the air
will always move if the flow passes along a horizontal pipe, but this is not the case. Instead, a specific
water speed is required to move the air; the greater the diameter of the pipe, the higher the airspeed is
required to move it away from the flowmeter.
Typically, most installations of flowmeters are simply sized on the diameter of the tube or on the flow
rate in the pipe, which means that the speed is often less than 0.5 m/s, which can be very problematic
if the air pockets occur.
As an example in a pipe with zero gradients, these are the specific water speeds necessary to move
away the air pockets detected in the tube:
• DN50 → 0.4 m/s
• DN150 → 0.7 m/s
• DN300 → 1 m/s
• DN600 → 1.5 m/s