Centrifugal Pump Troubleshooting Guideline

Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery – (wikipedia).

It’s a very important device for solids control process. Centrifugal pump is the ideal equipment to provide impetus for shale shaker, desander, desilter and jet mud mixer. Aipu solids control  offers a complete line of centrifugal pumps to accommodate a full variety of drilling applications. Sizes range from 3 x 2 to 8 x 6.

Troubleshooting Guideline

PUMP WILL NOT REACH DESIGN FLOW RATE

A. Insufficient NPSH (noise may or may not be present).

• Redesign suction piping; possibly enlarge diameter;
• Keep elbows, and so forth, at a minimum.

B. System head requirements greater than anticipated.

• Redesign system piping; possibly enlarge diameter;
• Keep elbows, and so forth, at a minimum;
• Increase impeller diameter.

C. Plugged impeller, suction line, or pump casing by fibrous or settled solids

• Clean and install strainer over suction line;
• For fibrous material, possibly enlarge pump.

D. Entrained air from atmosphere

• Check suction-line fittings and gaskets for leaks;
• Repack pump stuffing box;
• Check suction pit for vortex;
• Check for minimum suction-line submergence;
• Check degasser.

E. RPM too slow

• Check motor speed.

F. Wrong rotation direction

• Reverse any two of the three leads on a three-phase motor.

G. Impeller worn, has improper clearance, etc.

• Inspect impeller and reset to proper clearance;
• If worn, replace.

CENTRIFUGAL PUMP NO DISCHARGE OR FLOW

A. Motor horsepower too small

• Replace motor with larger size and proper rpm;
• Motor cannot rotate impeller.

B. Not properly primed

• Repeat priming operations;
• Try to have a flooded suction.

C. Suction lift too high

• Rearrange piping;
• Increase suction head;
• May need larger impeller;
• Check motor speed;
• May need larger pump for higher suction lift;
• Check suction line and pump for plugging;
• Check direction of rotation; if incorrect, change any two leads to motor;
• Check for entrained air or gas;
• Move centrifugal pump down to a lower level.

PUMP OPERATES BUT CONTINUALLY LOSES PRIME

A. Insufficient NPSH

• Redesign suction piping; possibly enlarge diameter.
• Keep elbows, and so forth, at a minimum.

B. Check for entrained air or gas.

C. If small whirlpools appear on top of liquid level, install baffle plate

EXCESSIVE NOISE—WET END

A. Cavitation—insufficient NPSH

• Redesign suction piping; possibly enlarge diameter;
• Keep elbows, and so forth, to a minimum;
• Abnormal fluid rotation due to complex piping.

B. Impeller rubbing

• Inspect and reset impeller;
• Inspect bearing assemblies for end play.

EXCESSIVE NOISE—POWER END

A. Overloaded bearing with races flaking or pitting

• Suction pressure and/or fluid specific gravity may exceed bearing design.

B.Bearing contamination—raceways scoured, pitted, or rusted

• Work with clean tools and clean the area around centrifugal pump; provide cover from wash-down water;
• Clean pump housing before removing;
• Use clean solvents and flushing oil;
• Protect bearings from moisture when not in use (wrap in clean paper or clean cloth);
• Clean interior of pump housing before replacing bearings;
• Inspect oil lip seals;
• Inspect plugs and tapped openings for tight closure.

C. Worn bearings

• Inspect and replace bearings;
• Improper lubrication including brown or bluish discoloration on races; stiff, cracked grease; failure of ball retainer; dirty or improper amount of lubricant; improper lubricant grade(s);
• Check shaft straightness;
• Check bearing alignment;
• Check housing bore for alignments.

D. Check for electric arcing from static electricity, electrical leakage, or short circuiting.

EXCESSIVE LEAKAGE OF A PACKED CENTERIFUAL PUMP STUFFING BOX

A. Loose packing gland

• Adjust packing gland while pump is running.

B. Packing excessively worn or improperly lubricated

• Replace packing and inspect for proper lubrication

C. Bent or scoured shaft

• Replace shaft and inspect pump for cause.

EXCESSIVE VIBRATION

A. Steady, regular vibration

• Inspect shaft balance and straightness;
• Check motor—shaft alignment; inspect coupling;
• Check baseplate bolting and grouting.

B. Unsteady vibration

• Bad bearings (largest vibration should be near the bad bearing)

C. Random, extremely high vibration

• Possible cavitation; improve suction piping layout.

D. Vibration disappears when power is off

• Check current cps

Note: When mounting a bearing on a shaft, use a proper size ring and apply pressure against the inner rings. When mounting in a housing, press against the outer ring. Apply pressure slowly and evenly.