Appendices
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©
2021
– Valeport Ltd
APPENDICES
Group Calibration of the 8011 Series Impeller
As fitted to the Valeport "Braystoke" BFM001 flowmeter
Definition
The calibration given here is not that of any individual meter, but one synthesised from tests
carried out at the Hydraulics Research Station, Wallingford, UK in March 1981 on a sample batch
of 19 instruments with rod suspension. The calibration is based upon standards set by the British
Standards Institution, BS3680, Part 8A, 1973.
Application
It applies to the BFM001 Meter fitted with the 125 mm (5 inch) diameter impeller, but only those
fitted with the 8011 series impeller, introduced from June 1981. A systematic error would result if
the calibration were applied, incorrectly, to any other type of Valeport meter.
Recognition
The prefix number 8011 is marked on the trailing edge of the impeller blades, together with the
individual serial number of the impeller. The 8011 series may also be recognised by:
i.
the blades taper in thickness from root to tip (some earlier meters had blades of uniform
thickness).
ii.
a 'land' or 'step' about 3mm wide on the impeller hub, forward to the leading edge of the blades
(on the preceding 475 series, the root of the impeller blade leading edge is flush with the
forward end of the hub).
Rating Equations and Table
Speed of Rotation, n
Speed of Flow, V
(rev/s)
(m/s)
Min
Max
0.07
0.32
0.013 + 0.2512 n
Equation 1
0.32
11.28
0.008 + 0.2667 n
Equation 2
Equation 1 extends from 0.031 to 0.093 m/s.
Equation 2 extends from 0.093 to 3.016 m/s.
These equations are evaluated in the attached ready-reference Calibration Chart, which covers the
full range of the general calibration.
Limited tests have shown that the calibration may be extended to about 18 rev/sec (5 m/s) without
significant loss of precision. The Calibration Chart is extended to include flow speeds up to 5 m/s.
The BFM001 may also be used successfully at flow speeds in excess of 5 m/s. The flow speed
should be calculated from the Rating Equation. There may however be a significant variation from
the computed flow speed and it is recommended that, if the Meter is to be used regularly at flow
speeds in excess of 5 m/s, an individual calibration of the Meter is undertaken.