What is a Centrifugal Pump?Common problems and solutions of centrifugal pumps.

 

 

 

Centrifugal pump is a common fluid mechanical equipment, which has the characteristics of high efficiency and energy saving, large flow, high head and simple maintenance. It uses centrifugal force to transport liquid from low pressure area to high pressure area, and is widely used in industry, construction, agriculture and chemical industry.

 

A centrifugal pump consists of a rotating pump shaft and one or more impellers. A centrifugal pump moves fluid by transferring rotational energy through a driven rotor with one or more impellers.The fluid enters the rapidly rotating impeller along its axis and is discharged through the impeller blade tips along its circumference under the action of centrifugal force. There are two different types of centrifugal pumps, radial flow centrifugal pumps and axial flow centrifugal pumps.

 

 

The main difference between radial and axial centrifugal pumps is the direction in which the fluid flows through the pump. In a radial centrifugal pump, the fluid enters the pump axially and is then directed radially outward by the impeller blades, which are perpendicular to the shaft. As the fluid passes through the impeller, the flow direction changes from axial to radial before leaving the pump at a right angle to the shaft. Radial flow centrifugal pumps are ideal for applications requiring high pressure or high head, such as chemical processes, water treatment or power stations.

 

In contrast, an axial flow centrifugal pump directs the fluid to flow parallel to the axis of the pump shaft. Fluid enters and exits the pump in the same direction, and the impeller blades rotate about the shaft, pushing the fluid through the pump. Axial flow centrifugal pumps are often used in applications that require high flow at low to medium pressures, such as in irrigation or cooling water systems.

 

In general, the choice of radial or axial flow centrifugal pump depends on the specific application requirements, including flow, pressure and fluid characteristics.

 

 

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Centrifugal pumps are widely used and trusted by all types of industrial plants, but that doesn't mean they don't encounter any problems. Here are the most common problems and brief solutions you need to know about centrifugal pumps.

 

1.NPSH

 

This occurs when the pressure in the pump body drops below the vapor pressure of the liquid, causing bubbles to form. These bubbles can then collapse, damaging the impeller and reducing the efficiency of the pump. The solution to this problem is to increase the pressure in the suction line or reduce the speed of the pump.

 

2.Pump running dry

 

Running a centrifugal pump dry or without adequate fluid is a significant problem as it can cause the pump to overheat, damage the impeller and reduce the efficiency of the pump. Centrifugal pumps rely on the pumped fluid to cool and lubricate the impeller and other moving parts.

 

When there is insufficient flow, the impeller and other components will generate heat due to friction, leading to overheating and potential damage. In addition, the lack of fluid can cause the impeller to rotate faster than it is supposed to, causing premature wear and damage. In extreme cases, a centrifugal pump running dry can cause the impeller to seize or the pump shaft to break, resulting in expensive repairs or replacements.

 

Therefore, it is vital to ensure that the centrifugal pump is always operating at sufficient flow to prevent damage and ensure optimal performance. The causes of insufficient flow in the pump may be:

1. Air in pump/pipes: Vent thoroughly and ensure all pipes and pump body are completely filled with liquid.
2. Suction lift too high: Check the inlet for any obstructions and verify that the static suction lift is correct.
3. Impeller rotation: Check the impeller rotation direction to make sure it is not reversed.
4. Incorrect speed: Check the power supply voltage and frequency, and make sure that the motor is not out of phase.
5. Blocked components: Check and clean valves, impellers and filters to ensure they are not blocked.

 

3. Impeller reverse rotation

 

Reverse rotation of the impeller in a centrifugal pump is a significant problem as it can cause poor pump performance, produce low flow rates, and potentially damage the impeller and other pump components.

Centrifugal pumps are designed to operate in a specified direction of impeller rotation, which is usually indicated by an arrow on the pump casing. Reverse impeller rotation causes the fluid to move in the opposite direction, which reduces efficiency and performance. This may also cause turbulence in the fluid, which can cause cavitation, erosion, and damage to the impeller and other pump components. In addition, reverse impeller rotation can cause excessive noise, vibration, and wear on the bearings, which may lead to premature failure.

 

Therefore, it is important to ensure that the centrifugal pump's impeller is rotating in the correct direction before operation to prevent poor performance and potential damage to the pump.

 

4. Pump leakage

 

Pump leakage is a significant problem as it leads to reduced efficiency, increased operating costs and potential safety hazards. Centrifugal pumps rely on seals and gaskets to prevent fluid from leaking from the pump casing or suction and discharge lines. When these seals and gaskets fail or wear, it can cause fluid to leak from the pump, resulting in reduced flow and efficiency.

 

5. Insufficient pump fluid supply

 

An underfilled or slow centrifugal pump is a significant problem as it can lead to downtime, reduced productivity and potential damage to the pump and other system components. Centrifugal pumps rely on a continuous supply of fluid to keep them in top condition and running efficiently. However, if a pump is underfilled due to air entering the suction line or for another reason, it can take some time to refill and get running again. An underfilled pump can cause significant downtime and reduced productivity, leading to lost production and revenue.

 

Additionally, during the refill process, the pump may be operating at low or no flow conditions, which can cause cavitation and potential damage to the impeller and other pump components.

 

Therefore, it is important to identify the root cause of pump starvation and take corrective actions, such as eliminating air leaks in the suction line, ensuring the pump is properly sized (specified) and installed, and using an automatic refill system to minimize downtime and reduce the risk of pump damage. Regular maintenance and inspections can also help identify and resolve potential starvation issues before they become major problems.

 

6.Pump vibration

 

Pump vibration can cause serious problems as it can lead to mechanical damage, reduced efficiency and increased operating costs. Pump vibration can be caused by various factors such as misalignment, bearing wear, impeller imbalance, cavitation, loose components, etc. Continuous vibration can lead to wear of pump components, reduced efficiency and potential failure. In addition, pump vibration can increase wear on shafts and bearings, which can increase maintenance and operating costs. In some cases, excessive vibration can damage other system components such as pipes or valves, leading to potential leaks and safety hazards.

 

Therefore, it is imperative to determine the root cause of pump vibration and take corrective action, such as realignment, replacing worn bearings or impellers, or adjusting the pump's operating conditions to prevent excessive vibration. Regular inspection and maintenance can also help identify and resolve potential vibration issues before they become major problems.

 

7.Pump Seizure

 

Seizure occurs when the rotor fails to turn within the pump housing. If seizure occurs, the motor overheats and trips the thermal overload protection device (fuse or circuit breaker). Pump seizure can have a number of causes, including foreign matter entering the pump, low flow, and/or operating at conditions other than the design. First check the pump for foreign matter, then check the impeller and power supply.

 

8.Chemical compatibility issues

 

Chemical compatibility issues in centrifugal pumps are a significant concern as they can cause corrosion, erosion and damage to the pump's components, reducing its efficiency and potentially causing leaks or failures. Centrifugal pumps are used to handle a wide variety of fluids, including corrosive and aggressive chemicals.

 

However, some chemicals may be incompatible with the materials used in pump construction, such as pump housings, impellers, seals and gaskets. When incompatible chemicals come into contact with these materials, they can cause chemical reactions that lead to corrosion, erosion and other forms of damage that can reduce the efficiency and service life of the pump.

 

Additionally, chemical compatibility issues can result in leaks, leading to safety concerns, environmental contamination, and potential fines or legal action. Therefore, it is important to ensure that the materials used in the pump construction are compatible with the fluid being pumped to prevent chemical reactions and potential damage to the pump and other system components. Regular inspections and maintenance can help identify and resolve compatibility issues before they cause significant damage.

 

9.Bearing overheating

 

This is another common problem with centrifugal pumps that is easy to diagnose. The bearings in a centrifugal pump should not be hot to the touch, and when bearing overheating occurs, it is usually a sign of impending trouble. Inspections should be carried out immediately (e.g. poor bearing installation, wear; improper lubrication, etc).