What is a multistage centrifugal pump used for?

What is a multistage centrifugal pump?

A multistage centrifugal pump is a pump that operates by using more than one impeller. Multiple impellers are used to generate more pressure to ensure fluid can reach long distances against gravity. The impellers are arranged in series. The pumped liquid moves through the first impeller, where its pressure is increased. The fluid proceeds to the second impeller, where pressure further increases. The process continues until the fluid leaves the last impeller with more pressure. As the name suggests, this pump uses centrifugal force to create a vacuum. The vacuum helps to suck fluid into the pump. The impellers have vanes so that during rotation the vanes add flow velocity and pressure to the pumped liquid. An electric motor or diesel engine powers the pump.

Figure: Multistage centrifugal pump.




Uses of multistage centrifugal pumps

  • Firefighting. Due to their high-pressure head and high flow rates, these pumps are used to put out fires in high-rise buildings and manufacturing plants.
  • Boiler feedwater. Thermal power plants need large volumes of water to generate steam. A large volume of water is transported using high-pressure, multistage pumps.
  • These pumps draw water from its source and transport it to agricultural land to irrigate crops.
  • They are used in commercial and domestic water supply and distribution.
  • These pumps are used in high-pressure cleaning because they generate high-pressure streams needed for cleaning dust and dirt.
  • They are used in the transportation of petroleum products.
  • These pumps are used in chemical processing.
  • Multistage pumps boost pressure in long-distance transportation of water and oil.
  • They are used in heating, ventilation, and air conditioning (HVAC) systems.
  • They are used in reverse osmosis.
  • They are used in water recirculation.
  • They are used in mine dewatering.

Advantages of multistage centrifugal pumps

  • High flow rate. These pumps transport large volumes of fluid within a second, making them suitable for large-scale use such as in boiler feed, irrigation, and municipal water supply among others.
  • High pressure. Due to the multiple impellers, these pumps generate high pressure suitable for overcoming high heads, thus capable of transporting fluids for long distances against gravity.
  • Versatile in size. Multistage centrifugal pump manufacturers design these pumps with various sizes for different heads and flow rates.
  • Versatile in applications. These pumps are used in various applications such as petroleum, chemicals, irrigation, water supply, firefighting, and HVAC among others.
  • They have high efficiency. The high efficiency is due to the pump’s ability to convert most of the power from the prime mover to hydraulic energy to move the fluid to the required destination. The high efficiency makes operating costs relatively lower.
  • These pumps are stable in performance.
  • Suitable for either vertical or horizontal orientation.
  • Highly durable. The pump is made of metallic solid materials to ensure its ability to withstand high pressure for decades of service.
  • The pump is highly reliable, primarily where it is used according to the multistage centrifugal pump manufacturer’s instructions.

Disadvantages of multistage centrifugal pumps

  • These pumps are more expensive compared to standard centrifugal pumps.
  • They consume more power relative to other pumps.
  • They are not suitable for pumping highly viscous fluids.

Troubleshooting multistage centrifugal pump

No fluid flow through the pump

  • The pump is not turned on. Turn the pump on.
  • No power supply. Ensure there is power on the motor cables.
  • The pump rotates in the reverse direction. Reverse the power cables connected the motor. Ensure the direction of motor/shaft rotation matches the direction of rotation indicated by an arrow on the pump casing.
  • The pump is not primed. Prime the pump entirely to remove air inside and in the suction line. The pump needs to remove all the air for it to generate vacuum and thus initiate flow.
  • Closed suction valve. Open the suction valve.
  • Closed discharge valve. Open the discharge valve.
  • Blocked suction line. Remove any material causing blockage.
  • Clogged strainer/impeller/foot valve. Check the impeller, foot valve, and filter for blockage and remove any foreign material.
  • The suction lift is too high. Lower the pump towards the fluid source or increase the fluid level in the tank.

Fluid flow rate reduces

  • Clogged impeller/check valve/strainer. Check for solids in these parts and remove them.
  • Leakage through the suction pipe. Repair the suction pipe.

Pump overheating

  • Dry running. Ensure there is fluid flow through the pump to help in cooling.
  • Shaft misalignment. Align the shafts properly.
  • Lack of lubrication. Lubricate the bearings adequately.
  • Flow is less than the minimum flow rate. Increase flow rate.

High vibrations

  • Clogged impeller. Clean off materials causing blockage.
  • Bent shaft. Replace the shaft.
  • Defective impeller. Repair/replace the impeller as necessary.
  • Misalignment. Align the shaft/coupling properly.

High noise levels

  • Poor lubrication. Lubricate bearings.
  • The pump operates above its duty range. Ensure the pump is within the duty point.

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