34
User Manual v2.0
MAG
4.6 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.
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
Fig. 48 | Pumping stations with flowmeters and vent valves
