8
Trouble-shooting
Pump is running but does not deliver
Flow rate insufficient
Discharge pressure not reached
Pump does not withdraw fluid (pump takes in air)
Excessive pump power input
Leakage at mechanical seal
Mechanical seal life too short
Mechanical seal damaged
Unusual vibrations and/or noises
Motor is overloaded
Table 15: Trouble-shooting
A B C D E
F
G H I
J
Possible cause
Remedy
4)
X X
Pump not primed sufficiently
Prime pump and check suction-side
conditions. Repeat pump start-up.
X X
X
Pump takes in air.
Check entire piping. Seal it, if required.
X X
X
In suction lift operation, air enters via
mechanical seal.
Replace mechanical seal or use seal with
reinforced spring.
X X
X
Clogged suction line or valves in piping
closed/not opened enough
Check suction line, remove any foreign
matter and check all valves.
X X
X
NPSHavailable smaller than pump's
NPSHrequired.
Improve suction and flow conditions. Reduce
flow rate with discharge-side control valve.
X X
Suction-side foot valve does not close
properly and liquid column drops.
Repair or replace foot valve.
X X X
Flow losses in system exceed specified
discharge head of pump.
Reduce pipe friction losses, fit larger impeller
(observe motor rating) or select different
pump which is suitable for the new duty
point.
X X X
Wrong direction of rotation or speed too
low (frequency inverter operation)
Check and correct the direction of rotation
or increase speed (observe motor rating).
X X X
X
Impeller clogged by foreign matter (on
pumps with closed impeller).
Remove foreign matter, clean impeller if
required.
X X
X
Excessive wear of mechanical seal
Replace complete mechanical seal.
X X
X
Excessive wear of impeller or clogged
impeller
Replace impeller or remove foreign matter.
X X
X Fluid viscosity higher than expected
Verify suitability of pump selection.
X X
Excessive gas content in fluid
Use vent valve.
X
Flow losses in system lower than specified
discharge head of pump
Reduce flow rate with discharge-side control
valve, reduce impeller diameter or fit orifice
plate.
X
X Fluid density higher than expected
Check motor rating and use larger motor (if
possible) or reduce flow rate.
X
Fluid viscosity too high for centrifugal pump Check suitability of different pump.
X
X
Flow rate too high
Reduce flow rate with discharge-side control
valve, reduce impeller diameter or fit orifice
plate.
X
Speed too high (frequency inverter
operation)
Reduce speed.
X
X
Impermissible friction. Impeller touches inner
wall of casing.
Repair and re-adjust pump.
X X X
X
Pump set not correctly aligned (radial or
angular shaft misalignment), or shaft run-
out
Re-align pump and motor or fit new pump
shaft.
X X
X
Incorrect electrical connection
Adjust electrical connection as required (only
to be performed by trained specialist
personnel).
X X
X
Electrical voltage does not match motor
used.
Use motor suitable for electric mains.
A
B
C
D
E
F
G
H
I
J
4)
Pump pressure must be released before attempting to remedy faults on parts which are subjected to pressure.
8 Trouble-shooting
Vitastage
35 of 44
