Short Answer:

Multistage pumping refers to the use of a pump that has more than one impeller mounted on the same shaft or connected in series. Each impeller increases the pressure of the fluid step by step, resulting in a higher total head. This arrangement is useful when a single pump cannot produce the required pressure or head. Multistage pumps are commonly used in high-pressure applications like boiler feed water, mine dewatering, and water supply systems.

In this system, the liquid is passed from one impeller to another, gaining energy at each stage. This makes the pump efficient and capable of handling large heads with moderate discharge. The design of multistage pumps helps in saving energy and ensuring smooth flow at high pressures.

Detailed Explanation :

Multistage Pumping

Multistage pumping is a method used to increase the head or pressure of a liquid by using two or more impellers connected in series within the same pump casing or multiple casings. Each impeller adds energy to the fluid, thereby increasing its pressure step by step. This system is mainly used when a single impeller pump cannot achieve the required discharge pressure or head.

In simple words, a multistage pump divides the total head requirement into several smaller heads, each produced by one impeller. When the fluid passes through all the impellers, the total head becomes the sum of the individual heads of all the impellers.

Construction of Multistage Pump

A multistage pump consists of several impellers mounted on the same shaft. Each impeller is placed in its own casing or section of the pump. The suction of the first impeller receives the liquid from the suction pipe. After gaining velocity and pressure, the liquid is passed to the inlet of the second impeller and continues through all stages until it reaches the discharge pipe.

The main components of a multistage pump include:

Impellers: Two or more impellers are used in series to increase the head.
Casing: It is divided into sections to accommodate multiple impellers.
Shaft: A common shaft holds all the impellers together.
Bearings: Support the shaft and ensure smooth rotation.
Suction and discharge nozzles: Guide the flow of liquid into and out of the pump.

Working of Multistage Pump

When the pump starts, the first impeller draws the fluid through the suction pipe and imparts kinetic energy to it. This kinetic energy is then converted into pressure energy as the fluid moves through the diffuser or volute casing. The fluid then enters the next impeller, where it again receives kinetic energy and pressure increases further. This process continues through all impellers, resulting in a high-pressure discharge at the outlet of the final stage.

For example, if one impeller produces a head of 50 meters and there are four impellers in the pump, the total head produced will be approximately 200 meters. This shows that by increasing the number of stages, the total head increases proportionally.

Types of Multistage Pumps

There are two main types of multistage pumps based on the direction of flow:

Horizontal Multistage Pump:
All impellers are mounted on a horizontal shaft. These pumps are easy to install and maintain and are commonly used in industrial and irrigation systems.
Vertical Multistage Pump:
The impellers are mounted on a vertical shaft. These pumps are compact and suitable for limited space and deep well applications.

Advantages of Multistage Pumping

Produces very high discharge pressure.
Efficient energy conversion due to staged pressure rise.
Compact and economical compared to single large impeller pumps.
Suitable for both high head and moderate flow rate applications.
Ensures smooth and controlled operation.

Applications of Multistage Pumping

Multistage pumps are widely used in:

Boiler feed water systems
Water treatment plants
High-rise building water supply
Mine dewatering
Pressure boosting systems
Firefighting systems

Example

If a system requires a head of 300 meters and one impeller can produce only 75 meters of head, then a 4-stage multistage pump can be used to meet the required pressure (4 × 75 = 300 meters). This shows how multistage pumping effectively meets high head requirements by using multiple impellers.

Conclusion

In conclusion, multistage pumping is a technique used to achieve high discharge pressure by connecting multiple impellers in series. Each stage adds energy to the fluid, and the total head is the sum of the individual stage heads. These pumps are efficient, reliable, and widely used in industries that require high pressure and continuous operation. Their ability to produce large heads without needing large impellers makes them a vital part of modern fluid handling systems.