Multistage Centrifugal Pumps: Types, Operating Principle

Centrifugal multistage pump

Centrifugal multistage pumps are fairly common types of dynamic hydraulic machines. They are quite widely used in water supply and wastewater systems, in the chemical and nuclear industries, in thermal power engineering, in aviation and rocket technology. This article describes what features of the devices, their advantages, and how to install the units yourself.

Types of centrifugal pumps

Units can be classified according to the following distinctive features:

By number of steps:

single-stage units;
two-stage;
multi-stage.

What is the number of fluid flows:

single-threaded;
with two streams;
multithreaded.

By what principle is liquid supplied to the impeller?

with spiral outlet;
along an annular outlet, with a guide vane;

What is the design of the impeller:

closed impeller;
open impeller.

How the drive is made:

using a coupling;
through the gearbox.

By shaft location:

vertical;
horizontal.

Glandless rotor pump. In this case, the engine rotor moves directly the fluid. The engine stator, which is constantly under voltage, is separated from the rotor by a special sleeve, 0.1 to 0.3 millimeters thick, made of stainless steel. The rotor bearings are lubricated by a liquid medium, which also performs the function of cooling the rotor. The pump shaft is mainly horizontal.
Dry rotor pump. Here the motor rotor does not come into contact with the liquid medium that is being pumped. They usually have a large fluid supply.

Advantages and disadvantages of centrifugal pumps

Compared to other types, centrifugal pumps have advantages:

In a wide range of flows Q, fairly high values of efficiency and pressure H are maintained, as a result of flat characteristics H = f(Q) and η = η (Q.
Increased rotation speed, which allows the pumps to be driven by electric motors and turbines.
The power change N has a smooth shape, which allows the pump to be started with the outlet valve closed or the check valve closed.
They have good stability in the operation of the devices and expansion of the technical values of H and Q with parallel and series connection of pumps, when working on one pipeline.
Transient processes occur smoothly when operating modes of hydraulic systems change.
The pumps are located above the liquid level in the flow tank.
Due to various factors, the performance of pumps H, Q, η changes. These factors are:

turning the diameters of impellers;
change in rotation speed;
change in frequency of power supply.

The low price of the pump, which is associated with the use of relatively inexpensive structural materials in the product:

become;
cast iron;
polymer materials.

Easy to maintain and operate.
High reliability during operation.
Large fluid supply Q.
Liquid flows with small, uniform pressure pulsations.
They work successfully on “contaminated” liquids.

The disadvantages of centrifugal pumps are:

The unit must be primed before starting it up.
They have a tendency to cavitation.
Reduced efficiency when pumping viscous liquids.
Low efficiency value with small liquid supply Q.
Centrifugal pumps are best used in the area of large water supplies Q and low and medium pressures H.

Advice: You cannot use such devices without first filling them with water.

What does this give?

Anyone who is familiar with the operation of compressor units will understand immediately.
In fact, the operating principle of multistage pumps is practically no different. The pumped liquid moves sequentially through sections, in each of which its pressure increases. The water pressure at the outlet of the device is determined by the total value created at each stage. This technical solution gives certain advantages to multistage pumps over traditional analogues.

One device, without additional elements included in the system, creates increased pressure in the pipe (up to 400 m). If we take into account that most private buildings have a complex water supply scheme, with several “points” for dispensing liquid and a significant distance from the source (well, borehole) from the house, this is a more than significant plus.
Relative noiselessness. There is no need to talk about the complete absence of sounds from a running engine, but their level is so insignificant that this is not taken into account. This can be explained simply - to create the required pressure, it makes no sense to use a large motor in the pump. In multi-stage models, the pressure increases due to the synchronous operation of several wheels. Consequently, they are characterized by an excellent combination of indicators such as power and generated pressure. This is already the third plus of devices in this group.

Do multistage pumps have any disadvantages?
From the point of view of practical application, there is only one - they are suitable only for working with clean liquids. It is understood that only the smallest fractions (contamination up to 100 g/m3) are allowed to be present in water, otherwise the efficiency of the device will sharply drop and the service life will be reduced. Many people put multi-stage pumps at a disadvantage because of their high price. Yes, they cost about 2.5 times more than traditional analogues. But an analysis of all aspects of their practical use shows that installing this particular device is sometimes more expedient. The fact is that to create the same pressure, if you purchase a model with one impeller, you will need a product with more power. And this characteristic directly affects its price. In addition, increased energy consumption cannot be discounted. Therefore, the savings are practically zero, and in terms of ease of installation (due to compactness), multistage pumps are preferable. And they are cheaper to operate.

How are devices in this group classified? They differ in the spatial orientation of the shaft on which the impellers are located. Vertical pumps are submersible models, while horizontal pumps are mainly surface pumps. To provide private buildings with water from an autonomous source, devices of the latest variety are mainly purchased. The fact is that they are more versatile and can be used for other purposes. For example, to increase pressure on the highway. You can get acquainted with one of the representatives of models of this type - MH 500C - its characteristics and cost by clicking on the link.

Operating principle of multistage centrifugal pumps

The instructions for multistage pumps indicate that they are used for pumping hot and cold water. In this case, they can be used to ensure:

Heat and water supply.
Increased pressure.
Fire fighting.
For feeding steam boilers.
Used in industrial circulation, washing, irrigation, air conditioning and watering systems.

A multistage centrifugal pump operates by rotating several wheels at once. In this case, the liquid that sequentially passes through the wheels moves quickly through the pipe. In this case, the pressure of the water supplied to the water supply system directly depends on the sum of the pressures of the elements arranged in succession and delivering the same supply. Each stage adds flow pressure, which depends on the power of the wheel, and the total pressure of the pump will be equal to the sum of the pressures of all its stages. Based on the location of the piston, pumps are divided into two types:

Horizontal. This device is an excellent option for increasing the pressure for water supply in an apartment or private house. Such a unit will successfully cope with the organization of autonomous water supply. Most often, horizontal pumps are made surface-mounted; their design does not involve immersion in the pumped medium. Devices are also used to solve more specific problems:

they are installed to install an irrigation system for the site;
to speed up the filling of the pool.

Vertical (see Centrifugal vertical pump: how to choose the right one). If the well is located near the house, the best option for providing water to the house would be to install a multi-stage vertical pump. With its help, you can pump out water from a depth of up to 20 meters, which is enough to satisfy the requirements of almost all customers.

Vertical multistage pumps

Horizontal multistage pumps (centrifugal)

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Purpose

The main task of using units of this type of pumping equipment is to create the highest possible pressure in water supply systems.
In other words, multistage centrifugal pumps are designed for pumping water or other non-aggressive liquid, the temperature of which can range from 0 to 1000C.

Multistage centrifugal pumps can be used to achieve the following purposes:

equipment for an autonomous water supply system for a private home;
irrigation and watering in agriculture;
ensuring uninterrupted water supply in city utilities;
automatic operation of fire extinguishing systems;
ensuring the operation of mine drainage;
feeding steam boilers of boiler plants;
pumping inactive chemical liquids in production, etc.

From the above points we can conclude that multi-stage centrifugal pumps are used in those areas of human activity where it is necessary to create high liquid pressure.

You may be interested in an article on the classification of centrifugal pumps. Read an article about methods for diagnosing and repairing centrifugal pumps with your own hands here.