6 Measuring point selection FLUXUS WW
UMFLUXUS_WWV1-1EN, 2018-02-28 25
6.2 Undisturbed flow profile
Some flow elements (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 selection 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.
The recommended straight inlet and outlet pipe lengths for different types of flow disturbance sources are shown in the ex-
amples in Tab. 6.2.
Tab. 6.2: Recommended distance from disturbance sources; D – nominal pipe diameter at the measuring point, l – recommended distance
disturbance source: 90° elbow
inlet: l ≥ 10 D outlet: l ≥ 5 D
disturbance source: 2 x 90° elbows on different levels
inlet: l ≥ 40 D outlet: l ≥ 5 D
disturbance source: valve
inlet: l ≥ 40 D outlet: l ≥ 5 D
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