Grundfos NK Serie Montage- Und Betriebsanleitung Seite 19

7.6 Expansion joints
Expansion joints provide these advantages:
• absorption of thermal expansion and contraction of pipework
caused by variations in liquid temperature
• reduction of mechanical influences in connection with
pressure surges in the pipework
• isolation of structure-borne noise in the pipework; this applies
only to rubber bellows expansion joints.
Do not install expansion joints to make up for
inaccuracies in the pipework, such as centre
Note
displacement or misalignment of flanges.
The expansion joints must be fitted at a minimum distance of 1 to
1 1/2 pipe diameters away from the pump on the suction and the
discharge side. This prevents turbulence in the joints, thus
ensuring optimum suction conditions and minimum pressure loss
on the discharge side. At flow velocities greater than 5 m/s, we
recommend fitting larger expansion joints matching the pipework.
Figures 15 and 16 show examples of rubber bellows expansion
joints with or without limiting rods.
Fig. 15 Rubber bellows expansion joint with limiting rods
Fig. 16 Rubber bellows expansion joint without limiting rods
Expansion joints with limiting rods can be used to reduce the
effects of the expansion/contraction forces on the pipework. We
always recommend 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 17 shows an example of a metal bellows expansion joint
with limiting rods.
Fig. 17 Metal bellows expansion joint with limiting rods
Due to the risk of rupture of the rubber bellows, metal bellows
expansion joints may be preferred at temperatures above +100
°C combined with high pressure.
7.7 Stuffing box piping
Pumps with stuffing box will always have a continuous leakage
during normal operation. We recommend to connect a drainage
pipe to the drain hole of the bearing bracket, pos. A, G1/2, to
collect the leaking liquid.
For pumps with stuffing box, type SNF, and external barrier liquid,
connect the drain pipe to the hole, pos. B, G1/8, before starting
the pump. The outlet hole for the external flushing pipe, pos. C, is
∅10.
A
Fig. 18 Pipe connections for stuffing box operation
C
B
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