A centrifugal pump is a hydraulic machine that converts mechanical energy into hydraulic energy using centrifugal force. These pumps are pretty popular in transferring liquid from low to high levels.

There are two types of centrifugal pumps depending upon the impeller. If a single impeller transfers liquid from a low to a high level, we call it a single-stage centrifugal pump. It is pretty simple in design and lightweight. 

But it has certain limitations. It cannot obtain a high head or pump liquid to a large distance. The efficiency is also a bit low.

So what should you do to pump water to a larger height? Well multistage centrifugal pump is an answer to this solution.

Whenever two or more impellers start to pump water, it is called a multistage centrifugal pump. The shafts can be mounted on the same shaft or different shafts. Multistage centrifugal pump has mainly two essential functions, i.e., to produce high and provide a large volume of water.

Whenever the impeller is connected in series and mounted on the same shaft, it provides a high head. But when the impeller is connected in parallel and mounted on different shafts, it will provide a large water discharge.

Multistage centrifugal pumps are a bit heavier in comparison to single-stage pumps. But they produce higher efficiency.

The article discusses more about multistage centrifugal pumps. So, keep reading this article to know more regarding the multistage pump, its working, advantages, and applications.

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Parts Of Multistage Centrifugal Pump

The components of the multistage centrifugal pump are listed below.

1. Suction Pipe

There are two ends of the suction pipe. Its one end is connected to the inner diameter impeller, and its other end is inserted inside the sump water level.

2. Strainer

The suction pipe’s end (dipped in the sump water level) consists of a strainer. The work of a strainer is to sediment the impurities or unwanted particles so that clean water can reach the impeller. 

Impure water or unwanted particles can create blockages in the centrifugal pump. So the strainer removes them before sending them to the impeller.

3. Foot Valve

The foot valve is a valve that allows water to flow in one direction. It is a unidirectional valve that opens only when the water from the sump moves toward the impeller.

Now if the centrifugal pump is running and it stops suddenly, then some water may move toward the suction pipe. In such a case, the foot valve closes so that no water will flow toward the sump.

4. Casing

It is the shell of the pump, and inside it impeller is present. There can be various types of casing like volute casing, vortex casing casing with guide blades.

5. Impeller

It is a rotor with a series of backward-curved blades—the rotor mounts on a shaft coupled to some external energy source. 

6. Delivery pipe

The delivery pipe has two ends. One end is connected to the casing, and the other to the point where we need to deliver water.

A delivery valve is there on the outlet of the delivery pipe. It is also a unidirectional valve that allows water to flow from the casing to the delivery pipe.

Working Of Multistage Centrifugal Pump

Before diving deep into the multistage centrifugal pump, we need to discuss the working of the centrifugal pump briefly.

The eye of the impeller is connected to the shaft. So whenever you switch on the centrifugal pump, the impeller starts to rotate and create a low-pressure zone. 

The water from the sump is at a high-pressure level. The foot valve opens, and the water moves toward the casing. 

The water rotates with the impeller, so kinetic energy is converted into pressure energy. It ultimately increases the pressure head of the water. The delivery valve opens, and water exits from a delivery pipe. But using a single-stage centrifugal pump cannot give us a high head.

Now if you use two or more centrifugal pumps and mount them on a single shaft, then it is called a multistage centrifugal pump in series and can yield high pressure of the water at the outlet of the delivery pipe. 

But connecting two or more centrifugal pumps on a different shaft is called a multistage centrifugal pump in parallel. It will yield high discharge or a large volume of water at the outlet of the delivery pipe. Let’s discuss them in detail.

Multistage Centrifugal Pump In Series 

Suppose two centrifugal pumps mount on a single shaft and connect in series. The water enters the first impeller and discharges at the outlet with a higher pressure. This water is then allowed to enter the second centrifugal pump. 

Now the water will be discharged at a pressure higher than the pressure at the outlet of the first impeller.

So, the water pressure increases when you connect two impellers on the same shaft. Now if you connect more than two impellers, then the pressure of the water will be increased accordingly.

Multistage Centrifugal pump in parallel

Suppose two centrifugal pumps are mounted on different shafts. Both the centrifugal pump discharges the water in a common pipe. But they lift water from the same sump.

The water delivery at the outlet of the first centrifugal pump is Q_1. The water delivered at the second centrifugal pump is Q₂. Both the centrifugal will discharge the water in a common pipe. So water that will finally go out from the outlet will discharge Q₁ +Q₂.

Types Of Multistage Centrifugal Pumps

There are two types of multistage centrifugal pumps. They are horizontal and vertical multistage centrifugal pumps.

1. Horizontal Multistage Centrifugal Pump

These pumps are installed in the horizontal direction and hence require more floor space. These pumps can handle fluid requiring high pressure in numerous industry and commercial applications. The applications include reverse osmosis, boiler feed, and many more.

2. Vertical Multistage Centrifugal Pump

These pumps are installed vertically. They take up a lot of installation space in the vertical direction. However, you can use them in areas with less horizontal space. It has a vertical shaft, and the impellers will stack one after another. 

These are used when you need to lift liquid from a low level to a high level. The applications of the vertical multistage centrifugal pump include boiler feed water, desuperheater feed, and many more.

Difference Between Horizontal And Vertical Multistage Centrifugal Pump

Horizontal Multistage Centrifugal Pump	Vertical Multistage Centrifugal Pump
1. Require more horizontal space to install	1. Require more vertical space to install
2. It requires more maintenance.	2. It requires less maintenance.
3. Expensive	3. Cheaper compared to a horizontal multistage centrifugal pump.
4. It usually handles fluid that requires high pressure in various industry applications.	4. It is mainly used to lift water from low to high levels.

Advantages Of Multistage Centrifugal Pump

• It generates more pressure in comparison to a single-stage reciprocating pump.
• It is highly versatile, i.e., various types of liquid like water, oils, and liquid can be used for pumping. Hence the multistage centrifugal pump can be used in multiple industry and commercial applications.
• Multistage centrifugal pumps are more efficient than single-stage pumps.
• They can handle large volumes of liquid.

Disadvantages of Multistage Centrifugal Pump

• Need a lot of space
• Complex operation
• High maintenance cost
• It has more rotating parts compared to a single-stage reciprocating pump.

Applications Of Multistage Centrifugal Pump

Multistage centrifugal pump has wide applications. We are listing some of them below.

• Reverse osmosis

Multistage centrifugal pumps can be sued for desalination purposes. These pumps pressurize the seawater through a membrane to obtain fresh water.

• Boiler feed water

It feeds water inside the boiler in power plants.

• Agriculture

 They can discharge a large volume of water or pump longer distances in agricultural fields.

• Snowmaking

It is used for pressurizing water to generate snow artificially.

• Fire Fighting

The firefighting department uses a multistage centrifugal pump to provide water at the outlet with high pressure to extinguish the fire.

Conclusion

Multistage centrifugal pumps are such pumps in which two or more impellers are used. They have wide applications like boiler feed, irrigation systems, chemical and process industries, etc. 

We have discussed the multistage centrifugal pump, its types, advantages, disadvantages, and applications, and we hope the information is helpful. You can ask us in the comment section if you have any doubts.