Measuring Instruments - Grundfos NB Serie Instrucciones De Instalación Y Funcionamiento

Fig. 21 Rubber bellows expansion joint without
limiting rods
Use expansion joints with limiting rods to reduce the
effects of the expansion or contraction forces on the
pipes. We always recommend that you use
expansion joints with limiting rods for flanges larger
than DN 100.
Anchor the pipes in such a way that they do not
stress the expansion joints and the pump. Follow the
supplier's instructions and pass them on to advisers
or pipe installers.
Figure 22 shows an example of a metal bellows
expansion joint with limiting rods.
Fig. 22 Metal bellows expansion joint with
limiting rods
Due to the risk of rupture of the rubber bellows, we
recommend that you use metal bellows expansion
joints at temperatures above +100 °C combined with
high pressure.

8.8 Measuring instruments

8.8.1 Pressure gauge and mano-vacuum gauge
To ensure continuous monitoring of the operation,
we recommend that you install a pressure gauge on
the outlet side and a mano-vacuum gauge on the
inlet side. Open the pressure gauge tappings only for
test purposes. The measuring range of the gauges
must be 20 % above the maximum pump pressure.
When measuring with pressure gauge on the pump
flanges, note that a pressure gauge does not register
dynamic pressure. On all NB, NBG pumps, the
diameters of the inlet and outlet flanges are different
which results in different flow velocities at the two
flanges. Consequently, the pressure gauge on the
outlet flange will not show the pressure stated in the
technical documentation, but a value which may be
up to 1.5 bar or approx. 15 m lower.
8.8.2 Ammeter
To check the motor load, we recommend that you
connect an ammeter.
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