Brochure

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6.4.2 Execution of force measurement
During force measurement the pump is mounted in a test bed, and the test
is made in the exact same way as a QH test. The force measurements are
made simultaneously with a QH test.
At the one end, the shaft is aected by the pressure in the pump, and in the
other end it is aected by the pressure outside the pump. Therefore the sys-
tem pressure has influence on the size of the axial force.
If comparison between the dierent axial force measurement is wanted, it
is necesarry to convert the system pressure in the axial force measurements
to the same pressure. The force aecting the shaft end is calculated by mul-
tiplying the area of the shaft end with the pressure in the pump.
6.5 Uncertainty in measurement of performance
At any measurement there is an uncertainty. When testing a pump in a test bed,
the uncertainty is a combination of contributions from the measuring equip-
ment, variations in the test bed and variations in the pump during the test.
6.5.1 Standard demands for uncertainties
Uncertainties on measuring equipment are in practise handled by specify-
ing a set of measuring equipment which meet the demands in the standard
for hydrualic performance test, ISO09906.
ISO09906 also states an allowed uncertainty for the complete measuring
system. The complete measuring system includes the test beds’ pipe circuit,
measuring equipment and data collection. The uncertainty for the com-
plete measuring system is larger than the sum of uncertainties on the single
measuring instrument because the complete uncertainty also contains vari-
ations in the pump during test which are not corrected for.
Variations occuring during test which the measurements can be correct-
ed for are the fluid’s characteristic and the pump speed. The correction is