SAMCO CP7, Instructions Manual

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14.Cavitation; insufficient
NPSH (depending on
installation).
15. Defective impeller.
16. Defective packing.
17. Foot valve too small or
partially obstructed.
18. Suction inlet not
immersed deep enough.
19. Wrong direction of
rotation.
20. Too small impeller
diameter (probable cause if
none of above).
a. Increase positive suction head on pump by lowering pump or
increasing suction pipe size or raising fluid level.
b. Sub-cool suction piping at inlet to lower entering liquid
temperature.
c. Pressurise suction vessel.
Inspect impeller. Replace if damaged or vane section badly eroded.
Replace packing and sleeves if badly worn.
Area through ports of valve should be at least as large an area of
suction pipe - preferably 1-1/2 times. If strainer is used, net clear area
should be 3 to 4 times of suction pipe.
If inlet cannot be lowered, or if eddies through which air is sucked
persist when it is lowered, chain a board to suction pipe. It will be
drawn into eddies, smothering the vortex.
Compare rotation of motor with directional arrow on pump casing.
Wrong rotation will cause pump damage.
Check with factory to see if a larger impeller can be used; otherwise,
cut pipe losses or increase speed-or both, as needed. But be careful
not to seriously overload drive.
Not Enough Pressure
21. Speed too low.
22. Air leaks in suction
piping.
23. Mechanical defects.
24. Obstruction in liquid
passages.
25. Air or gases in liquid.
(Test in laboratory,
reducing pressure on
liquid to pressure in
suction line. Watch for
bubble formation.)
26. Excessive impeller
clearance.
27. Too small impeller
diameter. (Probable cause
if none of above)
See item 5.
See item 8.
See items 15, 16 and 17.
Dismantle pump and inspect passages of impeller and casing.
Remove obstruction.
May be possible to overrate pump to point where it will provide
adequate pressure despite condition. Better to provide gas
separation chamber on suction line near pump, and periodically
exhaust accumulated gas. See item 14.
Adjust impeller clearance.
See item 20.