Fig. 4. Recommended locations of PEA pair
2.3.3. Length requirements for straight pipe runs
2.3.3.1. For proper operation of the flowmeter, before the first and the last PEA
with respect to the flow direction, there should be straight pipe runs of
corresponding length with the DN equal to the DN
of the CP. Table D.1
given in Appendix D shows minimum values of relative length of pipe-
line straight runs that should be used for typical installations.
The length of the straight pipe run L (mm) is calculated as follows:
DN
N
=
L
×
, (3)
where N is the relative length defined in the number of DNs and specified
in Table D.1;
DN – CP nominal diameter, mm.
CAUTION!
While measuring the reverse flow, all the PEAs are in
upstream position, and the length of the straight pipe runs shall be de-
fined in view of this condition.
If the required lengths of the straight pipe runs cannot be provided
at the estimated PEA location as per Appendix D, the on-site survey is
needed to specify the opportunities for individual measuring procedure
based on the measurement conditions at the particular site.
2.3.3.2. The lengths of straight pipe runs for the hydraulic resistance of “thermal
transducer in a protection sleeve” type can be defined in accordance
with the two bottom lines of the table in Appendix A (for plugged tap-
pings) provided that the following condition is observed:
D
t
/ D
i
>
0.1, (4)
Where D
t
is the diameter of the protection sleeve of the thermal trans-
ducer, mm;
D
i
is the pipeline inside diameter, mm.
If the condition D
t
/ D
i
<
0.1 is fulfilled, the thermal transducer’s hy-
draulic resistance may be neglected.
2.3.3.3. Any diaphragm or venturi type structure, as well as any valve, refer to
the type of hydraulic resistance specified in Appendix D as “control
valve”.
2.3.3.4. In case of mounting the straightening vane into the pipeline before the
measuring Pipe Section (Appendix E), reduction of straight pipe run
length is possible at the inlet of the CP up to two times. In this case, the
required length of the straight pipe run is defined on the base of site
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