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Pump School

Untitled Document

	Pump School
	Centrifugal Pumps
	Liquid Ring Vacuum Pumps
	Metering pumps

FAILURE DETECTION IN CENTRIFUGAL PUMPS

SYMPTOMS AND POSSIBLE CAUSES OF THE PROBLEM

SYMPTOMS	POSSIBLE CAUSES OF THE PROBLEM
Pump doesn't pump	1,2,3,4,6,11,14,16,17,22,48
Capacity is not sufficient	2,3,4,5,6,7,8,9,10,11,14,17,20,22,29,30,31,48
Manometric height is not sufficient	5,14,16,17,20,22,30,31
Pump loses priming after starting	2,3,5,6,7,8,11,12,13
Power absorbed is excessive	15,16,17,18,19,20,26,27,33,34,37,48,49
Leakage through the packing gland is excessive	13,26,32,34,35,36,38,39,40,49
Gaskets wearing too quickly	12,13,26,28,32,33,34,35,36,37,38,39,40,49
Mechanical seal wearing too quickly	15,16,17,23,24,25,26,27,28,34,35,36,38,40,41
Pump vibrates or is too noisy	2,3,4,9,10,11,21,26,27,28,30,35,36,41,42,43, 44,45, 46,47,48,49,50
Bearings life is too short	26,27,28,35,36,41,42,43,44,45,46,47,49
Pump overheats or seizes	1,4,21,22,27,28,35,36,41,49

Suction malfunctions:

1) Pump isn't primed
2) Pump or suction line is not completely full of liquid.
3) Suction height is too high
4) NPSH is insufficient
5) Liquid contains too much air or dissolved gasses
6) There are air pockets in the aspiration line.
7) Suction line is not hermetic and permits entry of air
8) There is entry of air in the pump through the packing gland
9) Valve at the foot of the line is undersized
10)Valve at the foot is partially obstructed.
11) Suction line is insufficiently submerged..
12) Flushing line is obstructed.
13) Position of the lantern ring in the gasket package is incorrect.

Installation malfunctions:

14) Revolution speed is too low.
15) Revolution speed is too high.
16) Direction of revolution is wrong.
17) Manometric height required in the installation is higher than that of the pump.
18) Manometric height required in the installation is lower than that of the pump.
19) Specific weight of the pumped fluid is different from projected.
20) Viscosity of the pumped fluid is different from projected.
21) Capacity of pump operating point too small
22) Pump is not suitable to work in parallel.
23) Material is not suitable for the liquid pumped.
24) Temperature of the liquid is too high.
25) Quantity or pressure of the flushing liquid is insufficient.

Mechanical malfunctions:

26) Shaft is bent.
27) Moving parts scrape fixed parts.
28) Bearings are worn.
29) Wear rings are worn.
30) Rotor is damaged.
31) Body joints are defective and permit internal leakage
32) Shaft or shaft sleeve are worn at the gasket operating area.
33) Shaft or shaft sleeve are worn at the mechanical seal operating area.
34) Type of mechanical seal or gasket is not suitable for working conditions.
35) Shaft turning off-center due to misalignment of bearings support or bearings wear.
36) Revolving part is unbalanced and causes vibrations.
37) Gland is too tight, causing insufficient flow of liquid in the gaskets.
38) Lack of cooling fluid in the packing box.
39) Excessive gap between end of the packing box and shaft causes penetration of the gasket into the pump.
40) Wear of the protection sleeve shaft caused by dirty and with suspensions flushing liquid.
41) Excessive loads caused by breaking of the mechanical seal or of the hydraulic balance device (if any).
42) Temperature of the bearings caused by excess oil or grease.
43) Lack of lubrication.
44) installation or unsuitable type of bearing (or damage occurred during assembly).
45) Dirty bearings.
46) Rusty bearings due to the presence of water inside the bearings support.
47) Excessive cooling of the bearings support with resulting condensation of humidity inside it.
48) Foreign bodies inside the rotor.
49) Misalignments.
50) Non-rigid foundations.