Vibration Damping; Expansion Joints - Grundfos NB Serie Instrucciones De Instalación Y Funcionamiento

8.6 Vibration damping

8.6.1 Elimination of noise and vibrations
In order to achieve optimum operation and minimum
noise and vibration, consider vibration damping of
the pump. Generally, always consider this for pumps
with motors of 11 kW and up. Vibration damping is
mandatory for motors of 90 kW and up. Smaller
motor sizes, however, may also cause undesirable
noise and vibration.
Noise and vibration are generated by the revolutions
of the motor and pump and by the flow in pipes and
fittings. The effect on the environment is subjective
and depends on correct installation and the state of
the rest of the system.
Elimination of noise and vibrations is best achieved
by means of a concrete foundation, vibration
dampers and expansion joints. See fig. 18.
8.6.2 Vibration dampers
To prevent the transmission of vibrations to
buildings, we recommend that you isolate the pump
foundation from building parts by means of vibration
dampers.
The selection of the right vibration damper requires
the following data:
• forces transmitted through the damper
• motor speed, taking speed control, if any, into
consideration
• required damping in % - suggested value is 70 %.
The selection of vibration damper will differ from
installation to installation. In certain cases, a wrong
damper may increase the vibration level. Vibration
dampers must therefore be sized by the supplier of
the vibration dampers.
If you install the pump on a foundation with vibration
dampers, always fit expansion joints on the pump
flanges. This is important to prevent the pump from
"hanging" in the flanges.
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8.7 Expansion joints

Expansion joints provide these advantages:
• absorption of thermal expansion and contraction
of pipes caused by variations in liquid
temperature
• reduction of mechanical influences in connection
with pressure surges in the pipes
• isolation of structure-borne noise in the pipes;
this applies only to rubber bellows expansion
joints.
Do not install expansion joints to make up
for inaccuracies in the pipes, such as
Note
centre displacement or misalignment of
flanges.
Fit the expansion joints at a minimum distance of 1 to
1 1/2 pipe diameters away from the pump on the inlet
and the outlet side. This prevents turbulence in the
expansion joints, thus ensuring optimum inlet
conditions and minimum pressure loss on the outlet
side. At flow velocities greater than 5 m/s, we
recommend that you fit larger expansion joints
matching the pipes.
Figures 20 and 21 show examples of rubber bellows
expansion joints with or without limiting rods.
Fig. 20 Rubber bellows expansion joint with
limiting rods