TROUBLE SHOOTING (CONT.)
CAUSES
16.Impeller partially plugged.
17.Cavitation; insufficient NPSHA (Net Positive Suction Head Available).
18.Defective impeller.
19.Foot valve too small or
partially obstructed.
20.Suction inlet not immersed deep enough.
21.Wrong direction of rotation.
22.System head too high.
23.Defective mechanical seal.
24.Speed too low.
25.Air leaks in suction piping or stuffing box.
26.Mechanical defects.
27.Vortex at suction inlet.
28.Obstruction in liquid passages.
29.Air or gases in liquid.
CURES
See item 9.
a.Increase positive suction head on pump by lowering pump or increasing suction pipe and fittings size.
b.
c.Pressurize suction vessel.
Inspect impeller, bearings and shaft. Replace if damaged or vane sections badly eroded.
Area through ports of valve should be at least as large as area of suction pipe (preferably 1.5 times). If strainer is used, net clear area should be 3 to 4 times area 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.
Symptoms are an overloaded driver and about one third rated capacity from pump. Compare rotation of motor with directional arrow on pump casing. If rotation is correct with arrow, impeller may have to be turned 180°. (See CHANGING ROTATION.)
See item 4.
Repair or replace seal.
Not Enough Pressure
See item 5.
See item 11.
See item 18.
See item 20.
Check to see if suction and discharge valves are fully open. Dismantle pump and inspect passages and casing. Remove obstruction.
May be possible to over rate pump to a point where it will provide adequate pressure despite condition. Better provide gas separation chamber on suction line near pump and periodically exhaust accumulated gas. See item 17.
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