DESMI Pumping Technology A/S
11
Tagholm 1
9400 Nørresundby
– Dänemark
Tlf. nr.: +45 96 32 81 11
Fax +45 98 17 54 99
E-mail: desmi@desmi.com
10. SYSTEM BALANCING
It is often difficult to calculate a manometric delivery head in advance. It is, however, decisively
important to the quantity of liquid delivered. A considerably smaller delivery head than expected will
increase the quantity of liquid delivered, causing increased power consumption and perhaps
cavitation in pump and piping. In the pump the impeller may show signs of heavy erosion caused by
cavitation (corrosion) which may at times render an impeller unfit for use in a very short time. Not
unusually do similar erosions occur in pipe bends and valves elsewhere in the piping system.
Therefore, after start-up, it is necessary to check either the quantity of liquid delivered or the power
consumption of the pump e.g. by measuring the current intensity of the connected electric motor.
Together with a reading of the differential pressure the quantity of water delivered can be determined
against the characteristics of the pump. Should the pump not function as intended, please proceed
according to the fault-finding list. Bear in mind, though, that the pump was carefully checked and
tested at the factory and that the majority of faults stem from the piping system.
FAULT
CAUSE
REMEDY
The pump does not
Prime
1. The pump is not filled
with liquid
2. Leaking non-return
valve in pump
3. Wrong direction of rotation
4. Air is drawn in because
of too little liquid or
leaking suction line
5. Liquid lock in outlet
line
6. Temperature of liquid
too high
7. Air cannot escape on
pressure side
Fill pump casing with liquid
Remove foreign body in
valve/Remove any coating
on mating faces
Change direction of
rotation
Lower suction pipe/
Tighten suction line
Change the pressure line
so that the air can pass out
freely
Replace liquid in pump
casing/Wrong dimen-
sioning/Contact DESMI
Ventilate the system
The pump has no or
too low capacity
1. Wrong direction of
rotation
2. Piping system choked
3. The pump is choked
4. Suction line leaks
Pump takes air
5. Suction lift too high
6. Pump and piping system
wrongly dimensioned
Change direction of
rotation to clockwise when
viewed from shaft end (the
direction of the arrow)
Clean or replace
Clean the pump
Find the leakage/repair the
fault, non-return valve not
submerged
Check data sheet Q/H
curve and NPSH or
contact DESMI
As 5
FAULT
CAUSE
REMEDY