Centrifugal pump troubleshooting: theory, problems and remedies

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Centrifugal pump troubleshooting: theory, problems and remedies

A water pump may stop working for many reasons, including the available water supply and the age of the pump. This article discusses centrifugal pumps and groups the main causes of failure into 10 topics:

1. The pump delivers no water

2. The pump delivers too little water

3. The pump produces insufficient water pressure

4. Water delivery starts and then stops

5. The pump requires abnormally high power

6. The stuffing box ( Stuffing Box) leaks excessively

7. The service life of the packing ( Packing) is shorter than normal

8. The pump vibrates or makes noise

9. The service life of the bearings ( Bearing) is abnormally short

10. The pump overheats during operation or is difficult to turn

1. The pump delivers no water: causes

- The pump was not primed before startup, or there is no water in the pumping chamber

- The pumping chamber or suction pipe is not completely filled with water

- The suction lift ( Suction lift) is too high

- NPSHa is lower than NPSHr

- There is an air pocket ( Air Pocket) in the suction pipe

- The end of the suction pipe is not sufficiently below the liquid surface

- The speed is too low

- The impeller rotates in the wrong direction

- The total system head exceeds the pump's design head

- Unsuitable pumps are operated together in parallel

- Foreign material is lodged in the impeller

2. The pump delivers too little water: causes

- The pumping chamber or suction pipe is not completely filled with water

- The suction lift ( Suction lift) is too high

- NPSHa is lower than NPSHr

- The liquid contains too many air or gas bubbles

- There is an air pocket ( Air Pocket) in the suction pipe

- The suction pipe leaks, allowing air to enter

- Air enters the pumping chamber through the stuffing box ( Stuffing box)

- The foot valve is too small

- The foot valve is blocked

- The end of the suction pipe is not sufficiently below the liquid surface

- The speed is too low

- The total system head exceeds the pump's design head

- The viscosity ( Viscosity) of the liquid differs from the design value

- Unsuitable pumps are operated together in parallel

- Foreign material is lodged in the impeller

- The wear ring ( Wearing ring) is badly worn

- The impeller is damaged

- The seal ( Gasket) of the pumping chamber is damaged, causing internal leakage

3. The pump produces insufficient water pressure

- The liquid contains too many air or gas bubbles

- The speed is too low

- The impeller rotates in the wrong direction

- The total system head exceeds the pump's design head

- The viscosity ( Viscosity) of the liquid differs from the design value

- Unsuitable pumps are operated together in parallel

- The wear ring ( Wearing ring) is badly worn

- The impeller is damaged

- The seal ( Gasket) of the pumping chamber is damaged, causing internal leakage

4. Water delivery starts and then stops: causes

- The pumping chamber or suction pipe is not completely filled with water

- The suction lift ( Suction lift) is too high

- The liquid contains too many air or gas bubbles

- There is an air pocket ( Air Pocket) in the suction pipe

- The suction pipe leaks, allowing air to enter

- Air enters the pumping chamber through the stuffing box ( Stuffing box)

- The end of the suction pipe is not sufficiently below the liquid surface

- The seal-water pipe is blocked, preventing water from reaching the seal and allowing air to enter the pumping chamber

- Installed Seal cage in the wrong position in the stuffing box ( Stuffing Box) preventing the seal water from

5. The pump requires abnormally high power: causes

- The speed is too high

- The impeller rotates in the wrong direction

- The total system head exceeds the pump's design head

- The total system head is below the pump's design head

- The specific gravity of the liquid differs from the design value

- The viscosity ( Viscosity) of the liquid differs from the design value

- Foreign material is lodged in the impeller

- The pump shaft and driver are misaligned

- The shaft is bent

- Rotating parts rub against stationary parts

- The wear ring ( Wearing ring) is badly worn

- The packing ( Packing) is incorrectly installed

- The type of packing is unsuitable for the operating conditions

- The gland ( Gland) is too tight, preventing lubricant from reaching the packing ( Packing)

6. The stuffing box ( Stuffing Box) leaks excessively: causes

- The shaft or shaft sleeve ( Shaft sleeves) is damaged at the packing ( Packing)

- The packing ( Packing) is incorrectly installed in the stuffing box ( Stuffing Box) preventing the seal water from working properly

- The type of packing is unsuitable for the operating conditions

- The shaft rotates out of alignment because of damaged bearings or misalignment between the pump and driver

- The impeller or other rotating parts are unbalanced, causing vibration

- No water flows to cool the stuffing box ( Stuffing Box) of the water-cooled type

- The clearance ( Clearance) between the shaft and pump casing ( Casing) at the bottom of the stuffing box is excessive, forcing the packing into the pumping chamber

- Dirt or grit in the seal water ( Sealing Liquid) scratches the shaft or shaft sleeve

7. The service life of the packing ( Packing) is shorter than normal: causes

- The packing ( Packing) is incorrectly installed

- The seal-water pipe is blocked, preventing water from reaching the seal and allowing air to enter the pumping chamber

- Installed Seal cage in the wrong position in the stuffing box ( Stuffing Box) preventing the seal water from flowing to perform its function

- The pump shaft and driver are misaligned

- The shaft is bent

- The bearing ( Bearing) is worn

- The shaft or shaft sleeve ( Shaft sleeves) is damaged at the packing ( Packing)

- The type of packing is unsuitable for the operating conditions

- The shaft rotates out of alignment because of damaged bearings or misalignment between the pump and driver

- The impeller or other rotating parts are unbalanced, causing vibration

- The gland ( Gland) is too tight, preventing lubricant from reaching the packing ( Packing)

- No water flows to cool the stuffing box ( Stuffing Box) of the water-cooled type

- The clearance ( Clearance) between the shaft and pump casing ( Casing) at the bottom of the stuffing box is excessive, forcing the packing into the pumping chamber

- Dirt or grit in the seal water ( Sealing Liquid) scratches the shaft or shaft sleeve

8. The pump vibrates or makes noise: causes

- The pumping chamber or suction pipe is not completely filled with water

- The suction lift ( Suction lift) is too high

- NPSHa is lower than NPSHr

- The foot valve is too small

- The foot valve is blocked

- The end of the suction pipe is not sufficiently below the liquid surface

- The pump is operated at a very low flow rate

- Foreign material is lodged in the impeller

- The pump shaft and driver are misaligned

- The pump and driver foundation is not sufficiently rigid and secure

- The shaft is bent

- Rotating parts rub against stationary parts

- The bearing ( Bearing) is worn

- The impeller is damaged

- The shaft rotates out of alignment because of damaged bearings or misalignment between the pump and driver

- The impeller or other rotating parts are unbalanced, causing vibration

- Excessive thrust is caused by damaged internal components or damaged equipment for balancing hydraulic pressure

- There is too much grease or lubricating oil in the bearing housing, or inadequate cooling causes a high temperature

- Lubricant is lacking

- Bearings are installed incorrectly, for example they crack or are damaged during installation, or the wrong size is used

- Dirt has entered the bearing or bearing housing

- Bearings develop rust because water can leak in

- Very cold pumped water causes water vapor to condense into droplets inside the bearing housing

9. The service life of the bearings ( Bearing) is abnormally short: causes

- The pump shaft and driver are misaligned

- The shaft is bent

- Rotating parts rub against stationary parts

- The bearing ( Bearing)  is worn

- The shaft rotates out of alignment because of damaged bearings or misalignment between the pump and driver

- The impeller or other rotating parts are unbalanced, causing vibration

- Excessive thrust is caused by damaged internal components or damaged equipment for balancing hydraulic pressure

- There is too much grease or lubricating oil in the bearing housing, or inadequate cooling causes a high temperature

- Lubricant is lacking

- Bearings are installed incorrectly, for example they crack or are damaged during installation, or the wrong size is used

- Very cold pumped water causes water vapor to condense into droplets inside the bearing housing

- Bearings develop rust because water can leak in

- Dirt has entered the bearing or bearing housing

10. The pump overheats during operation or is difficult to turn: causes

- The pump was not primed before startup, or there is no water in the pumping chamber

- NPSHa is lower than NPSHr

- The pump is operated at a very low flow rate

- Unsuitable pumps are operated together in parallel

- The pump shaft and driver are misaligned

- Rotating parts rub against stationary parts

- The bearing ( Bearing) is worn

- The shaft rotates out of alignment because of damaged bearings or misalignment between the pump and driver

- Excessive thrust is caused by damaged internal components or damaged equipment for balancing hydraulic pressure