FLUXUS F808, F809 5 Selection of the measuring point
22 UMFLUXUS_F808_8091V1-2-1EN, 2019-08-23
5.2 Undisturbed flow profile
Some flow elements (e. g., elbows, slide valves, valves, control valves, pumps, reducers, diffusers, etc.) distort the flow
profile in their vicinity. The axisymmetrical flow profile needed for correct measurement is no longer given. A careful selec-
tion of the measuring point helps to reduce the impact of disturbance sources.
It is most important that the measuring point is chosen at a sufficient distance from any disturbance sources. Only then it
can be assumed that the flow profile in the pipe is fully developed. However, measuring results can be obtained even if the
recommended distance to disturbance sources cannot be observed for practical reasons.
Recommended straight inlet and outlet pipe lengths for different types of flow disturbance sources are shown in the ex-
amples in Tab. 5.2.
Tab. 5.2: Recommended distance from disturbance sources;
D - nominal pipe diameter at the measuring point, l - recommended distance between disturbance source and transducer position
disturbance source: 90° elbow
supply line: l ≥ 10 D return line: l ≥ 5 D
disturbance source: 2 x 90° elbow in different planes
supply line: l ≥ 40 D return line: l ≥ 5 D
disturbance source: valve
supply line: l ≥ 40 D return line: l ≥ 5 D
l
l
l
l
l
l
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