Johnson Pump MCHZ Instruction Manual page 27

26
Table 3: Possible causes of pump failures.
Possible causes
1 Pump or suction pipe is not sufficiently filled or de-aerated
2 Gas or air coming from the liquid
3 Air lock in the suction pipe
4 Air leak in the suction pipe
5 The pump takes in air through the stuffing box packing
8 The manometric suction head is too high
9 Suction pipe or suction strainer is blocked
10 Insufficient immersion of foot valve or suction pipe during operation of the pump
11 NPSH available too low
12 Speed too high
13 Speed too low
14 Wrong sense of rotation
15 Pump does not operate at the right duty point
16 Liquid density differs from the calculated liquid density
17 Liquid viscosity differs from the calculated liquid viscosity
18 Pump operates when the liquid flow is too low
19 Wrong pump selection
20 Obstruction in impeller or pump casing
21 Obstruction in the piping
22 Wrong installation of the pump unit
23 Pump and motor not well aligned
24 Rotating part running out of true
25 Imbalance in rotating parts (for instance: impeller or coupling)
26 Pump shaft is running out of true
27 Bearings faulty or worn out
28 Casing wear rings faulty or worn out
29 Damaged impeller
30 Shaft on the spot of the stuffing box packing rings or seal faces of the mechanical seal
are worn out or damaged
31 Worn out or dried out stuffing box packing rings
32 Not well packed stuffing box packing or bad mounting of the mechanical seal
33 Stuffing box packing type or mechanical seal not suitable for the pumped liquid or
operation circumstances
34 Gland or mechanical seal cover has been tightened too much or crookedly
37 Axial retaining of impellers or pump shaft is defective
38 The bearings have been mounted wrongly
39 Too much or too little bearing lubrication
40 Wrong or polluted lubricant
41 Impurities in the liquid get into the stuffing box packing
42 Too high axial force because of excessive inlet pressure
43 Excessive pressure in stuffing box packing space due to too much play in the throttling
bush or blocked by-pass
Problem solving
MCHZ/EN (0912) 4.2