Measuring Instruments - Grundfos LSV Montage- Und Betriebsanleitung

3.4.5 Auxiliary pipes
Drains
Install the drain pipes from the pump casing and
stuffing boxes to a convenient disposal point.
Flushing pipes
• Pumps fitted with stuffing boxes
When the inlet pressure is below the ambient
pressure, supply the stuffing boxes with liquid to
provide lubrication and prevent the ingress of air. This
is normally achieved via a flushing pipe from the
outlet side to the stuffing box. You can fit a control
valve or orifice plate in the flushing pipe to control the
pressure to the stuffing box.
If the pumped liquid is dirty and cannot be used for
flushing the packing rings, we recommend a separate
clean, compatible liquid supply to the stuffing box at 1
bar (15 psi) above the inlet pressure.
• Pumps fitted with mechanical seals
Seals requiring recirculation will normally be provided
with a flushing pipe from the pump casing.

3.4.6 Measuring instruments

To ensure continuous monitoring of operation, we
recommend that you install pressure gauges on the
pump inlet and outlet flanges. The pressure gauge on
the inlet side must be capable of measuring vacuum.
The pressure tappings must only be opened for test
purposes. The measuring range of the outlet side
pressure gauge must be minimum 20 % above the
maximum pump outlet pressure.
When measuring with pressure gauges on the pump
flanges, note that a pressure gauge does not register
dynamic pressure (velocity pressure). The diameters
of the inlet and outlet flanges are different, and this
results in different flow velocities in 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
lower.
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