Common faults and treatment methods of centrifugal pump

Centrifugal pump is widely used in industry, and various faults are easy to occur in operation. Therefore, planned inspection, repair and maintenance must be carried out to prevent accidents. Sorted out the common fault types of centrifugal pump, let’s have a look!

The priority working range of centrifugal pump is that in engineering design, in order to ensure that the centrifugal pump has high efficiency and low vibration value during operation, its working point is generally required to fall within 70% – 120% of the flow at the best efficiency point.
If the working point of the centrifugal pump deviates from the priority working range and falls between the limit working range and the priority working range, although it can also operate safely for a long period of time, the efficiency will decline rapidly. Generally, centrifugal pumps have a maximum allowable flow and a minimum continuous stable flow.

The pump cannot be started or the starting load is large

(1) The prime mover or power supply is abnormal.
Solution: check the power supply and prime mover.
(2) Pump stuck.
Handling method: turn the coupling by hand for inspection and disassemble it if necessary to eliminate the faults of dynamic and static parts.
(3) The packing is pressed too tightly.
Treatment method: loosen the filler.
(4) Discharge valve is not closed.
Treatment method: close the discharge valve and restart.
(5) The balance pipe is not unobstructed.
Treatment method: dredge the balance pipe.

The pump cannot be started or the starting load is large

(1) Insufficient pump filling (or the gas in the pump is not exhausted).
Treatment method: refill the pump.
(2) The pump is not steering correctly.
Treatment method: check the rotation direction.
(3) The pump speed is too low.
Treatment method: check the speed and increase the speed.
(4) The filter screen is blocked and the bottom valve is not working.
Treatment method: check the filter screen to eliminate sundries.
(5) The suction height is too high, or there is a vacuum in the suction tank.
Treatment: reduce the suction height; Check the suction tank pressure.

Interruption after pump discharge

(1) Air leakage in suction pipeline.
Treatment method: check the pipe connection at the suction side and the sealing of the stuffing box.
(2) The gas at the suction side is not completely discharged during pump filling.
Treatment method: refill the pump.
(3) The suction side is suddenly blocked by foreign matters.
Treatment method: stop the pump to deal with foreign matters.
(4) Inhale a large amount of gas.
Treatment method: Yes, check whether there is vortex at the suction inlet and whether the submergence depth is too shallow.

Insufficient flow

(1) Same as B, C.
Treatment method: take corresponding measures.
(2) The static head of the system increases.
Treatment method: check the liquid height and system pressure.
(3) Resistance loss increases.
Treatment method: check the pipeline, check valve and other obstacles.
(4) The wear ring of housing and impeller is too worn.
Treatment method: replace or repair the wear ring and impeller.
(5) Leakage at other parts.
Treatment method: check the shaft seal and other parts.
(6) The pump impeller is blocked, worn and corroded.
Treatment method: cleaning, inspection and replacement.

Insufficient lift

(1) The same as B’s (1), (2), (3), (4), C’s (1), D’s (6).
Treatment method: take corresponding measures.
(2) The impeller is installed reversely (double suction wheel).
Treatment method: check the impeller.
(3) The liquid density and viscosity are inconsistent with the design conditions.
Treatment method: check the physical properties of the liquid.
(4) Too much flow during operation.
Treatment method: reduce the flow.

Power consumption in operation

(1) There is friction between impeller and wear ring, impeller and shell.
Treatment: check and repair.
(2) The same as item (4) of E.
Treatment method: reduce the flow.
(3) Liquid density increases.
Treatment method: check the liquid density.
(4) The packing is pressed too tightly or dry friction.
Treatment method: loosen the packing and check the water seal pipe.
(5) The bearing is damaged.
Treatment method: check, repair or replace the bearing.
(6) The speed is too high.
Handling method: check the driver and power supply.
(7) The pump shaft is bent.
Treatment: correct the pump shaft.
(8) Axial force balancing device failed.
Treatment method: check whether the balance hole and return pipe are blocked.
(9) The coupling is poorly aligned or the axial clearance is too small.
Treatment method: check the alignment and adjust the axial clearance.

Pump vibration or abnormal sound

(1) The same as (4) of C and (5), (7) and (9) of F.
Treatment method: take corresponding measures.
(2) The vibration frequency is 0 ~ 40% of the working speed. Excessive bearing clearance, loose bearing bush, impurities in the oil, poor oil quality (viscosity and temperature), foaming of oil due to air or process liquid, poor lubrication and bearing damage.
Treatment method: after inspection, take corresponding measures, such as adjusting bearing clearance, removing impurities in oil and replacing new oil.
(3) The vibration frequency is 60% ~ 100% of the working speed. The bearing problems are the same as (2), or the seal clearance is too large, the retainer is loose, and the seal is worn.
Treatment method: check, adjust or replace the seal.
(4) The vibration frequency is twice the working speed. Misalignment, loose coupling, friction of sealing device, shell deformation, bearing damage, support resonance, thrust bearing damage, shaft bending and poor fit.
Treatment method: check, take corresponding measures, repair, adjust or replace.
(5) The vibration frequency is n times the working speed. Pressure pulsation, misalignment, shell deformation, seal friction, support or foundation resonance, pipeline and machine resonance.
Treatment method: the same as (4), strengthen the foundation or pipeline.
(6) The vibration frequency is very high. Shaft friction, seal, bearing, imprecision, bearing jitter, poor shrinkage fit, etc.
Treatment method: the same as (4).

Bearing heating

(1) The scraping and grinding of bearing pad is not qualified.
Treatment method: repair the bearing pad or replace it.
(2) The bearing clearance is too small.
Treatment method: readjust the bearing clearance or scrape.
(3) Insufficient lubricating oil and poor oil quality.
Treatment method: increase the oil quantity or replace the lubricating oil.
(4) Poor bearing assembly.
Treatment method: check the bearing assembly as required to eliminate unqualified factors.
(5) Cooling water open circuit.
Treatment method: Inspection and repair.
(6) The bearing is worn or loose.
Treatment method: repair the bearing or scrap it. If loose, retighten relevant bolts.
(7) The pump shaft is bent.
Treatment: correct the pump shaft.
(8) The oil slinger is deformed, the oil slinger cannot rotate and cannot be oiled.
Treatment method: renew the oil slinger.
(9) The coupling is poorly aligned or the axial clearance is too small.
Treatment method: check the alignment and adjust the axial clearance.

Shaft seal heating

(1) The packing is pressed too tightly or rubbed.
Treatment method: loosen the packing and check the water seal pipe.
(2) The water seal ring is misaligned with the water seal pipe.
Treatment method: recheck the alignment.
(3) Good flushing and cooling.
Treatment method: check and flush the cooling circulating pipe.
(4) The mechanical seal is faulty.
Treatment method: check the mechanical seal.

Large rotor movement

(1) Improper operation, and the operating conditions are far away from the design conditions of the pump.
Treatment method: operate strictly to make the pump always operate near the design working condition.
(2) Poor balance.
Treatment method: dredge the balance pipe.
(3) The materials of balance disc and balance disc seat are unqualified.
Treatment method: replace the balance disc and balance disc seat whose material meets the requirements.

Occurrence of water hammer

(1) Due to the sudden power failure, the system pressure fluctuates, the negative pressure of the discharge system occurs, and the bubbles dissolved in the liquid escape, resulting in gas in the pump or pipeline.
Treatment method: exhaust the gas.
(2) Due to the sudden power failure, the high-pressure liquid column poured back rapidly and impacted on the valve plate of the check valve at the pump outlet.
Treatment method: it is to transform the layout of pipes and pipe accessories of the unreasonable discharge system of the pump.
(3) The valve of the outlet pipe closes too fast.
Solution: slowly close the valve.

Source: China Pipe Fitting Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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