What are the two primary parts of a pump?

Learn the basics of centrifugal pumps, how they work, the different types and where we use them.

Learn the basics of centrifugal pumps, how they work, the different types and where we use them.

Scroll to the bottom to watch the YouTube tutorial.

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What Does a Centrifugal Pump Look Like?

Centrifugal pumps come in many shapes, colours and sizes but they typically look something like this.

Centrifugal Pump

The pumps consist of two main parts, the pump and the motor. The motor is an electrical induction motor which allows us to convert electrical energy into mechanical energy. This mechanical energy is used to drive the pump and move the water. The pump pulls water in through the inlet and pushes it out through the outlet. 

Pump and Electrical Motor of Centrifugal Pump

Inside a Centrifugal Pump

As we take the unit apart, we can see that we have a fan and protective casing mounted at the back of the electrical motor. Then inside the motor we have the stator, mounted to the motors casing, which holds the copper coils, and we’re going to look in detail at that a little later in this video. Concentric to this we have the rotor and shaft. The rotor rotates and as it rotates so does the shaft. The shaft runs along the entire length from the motor and into the pump. This then connects onto the pumps impeller. Some models of centrifugal pumps, like this one, will have a separate shaft for the pump and the motor. Separated shafts are joined using a connection known as a coupling. Coupled pumps will usually have a bearing house which, as the name suggests, houses the bearings.

Inside a Centrifugal Pump

The shaft continues into the pump casing. As it enters the casing it passes through a gland, packing and the stuffing box which combine to form a seal. The shaft then connects onto the impeller.

Discharge Outlet and Suction Inlet

The impeller imparts a centrifugal force onto the fluid which enables us to move liquids, such as water, through a pipe. The impeller is enclosed within the pump casing. The casing contains and directs the flow of water as the impeller pulls it in and pushes it out. Therefore we have a suction inlet and a discharge outlet. 

How Does The Centrifugal Pump Work?

At the back of the electrical motor, we see that the fan is connected to the shaft. When the motor rotates the shaft, the fan will therefore also rotate. The fan is used to cool down the electrical motor and it will blow ambient air over the casing to dissipate the unwanted heat. If the motor becomes too hot, the insulation on the coils inside the motor will melt causing the motor to short circuit and destroy itself. The fins on the outside perimeter of the casing increase the surface area of the casing which allows us to remove more unwanted heat.

Fins increase the surface area.

The electrical motor comes in either three phase or single phase configuration, depending on the application.

We’re going to look at three phase as it’s the most common. Inside the 3 phase induction motor we have 3 separated coils which are wound around the stator. Each coil set is connected to a different phase to produce a rotating magnetic field. 

Three phase induction motor

When we pass AC, or alternating current, through each coil, the coil will produce an electromagnetic field which changes in intensity as well as polarity as the electrons passing through it change direction between forwards and backwards.

Alternating Current

But, if we connect each coil to a different phase, then the electrons will change direction between forwards and backwards at different times compared to the other phases. This means that the magnetic field of each coil will change in intensity as well as polarity at different times compared to the other phases.

Different Phases

To distribute this magnetic field, we rotate the coils 120 degrees from the previous phase and insert them into the stator of the motor casing. This will create the effect of a rotating magnetic field. At the centre of the stator we place the rotor and shaft. The rotor will be affected by the rotating magnetic field and will force it to also rotate. 

Rotor and Shaft

The rotor is connected to the shaft and the shaft runs from the fan, through the rotor, all the way up to the impeller. This way when the rotor rotates, so will the impeller. So now, by creating the rotating magnetic field within the motor, we spin the rotor which spins the shaft and this spins the impeller.

Looking at the pump casing, we find a channel for water to flow along which is called the volute. This volute spirals around the perimeter of the casing up to the pump outlet, this channel increases in diameter as it makes it way to the outlet.

Volute

The shaft passes through the seals and into the pump casing where it connects to the impeller. 

There are many types of impeller but most will have these backwards curved vanes which will either be open, semi open or closed in with some shrouds.

Closed, Semi-Open or Open

These backwards curved vanes do not push the water. The curves rotate, with the outer edge moving in the direction of the expanding volute. These vanes will provide the fluid with a smooth path for the water to follow. We’ll see that a little later in the video.

The impeller is submerged in water. When the impeller rotates, the water within the impeller will also rotate. As the water rotates, the liquid is radially pushed outwards in all directions to the edge of the impeller and into the volute. As the water moves outwards off the impeller it creates a region of lower pressure which pulls more water in through the suction inlet. The water enters into the eye of the impeller and is trapped between the blades.

The liquid is radially pushed outwards

As the impeller rotates it imparts kinetic energy, or velocity, onto the water. By the time the water reaches the edge of the impeller it has reached a very high velocity. This high speed water flows off the impeller, and into the volute, where it hits the wall of the pump casing. This impact converts the velocity into potential energy or pressure. More water follows behind this and so a flow develops. The volute channel has an expanding diameter as it spirals around the circumference of the pump casing. As it expands, the velocity of the water will decrease resulting in the pressure increasing. This expanding channel therefore allows more water to keep joining and converting into pressure.

So the discharge outlet is therefore a higher pressure than the suction inlet. The high pressure at the discharge allows us to force the fluid through pipes and into a storage tank or around a pipe system.

Forces fluid through pipes into a storage tank

The thickness of the impeller and the rotational speed affects the volume flow rate from the pump but the diameter of the impeller and the rotational speed will increase the pressure it can produce.

NPSH

A term you’re going to hear is NPSH which is the acronym for Net Positive Suction Pressure. We’ll briefly cover what this means.

NPSHR

There are two letters at the end of this acronym the NPSHR and the NPSHA. The R is the required NPSH. Each pump is tested for this value and this can be obtained from the pump manufacturer via the pumps operating chart. Don’t worry about this confusing looking chart at this point, we’re going break it down and cover that in detail in a dedicated article. The R value is basically a warning or danger point. As water enters the pump and flows into the impellers eye it experiences a loss of energy due to friction, this gives us a pressure drop. At certain conditions the water flowing through this section can reach boiling point, when this occurs we refer to this as cavitation. We’ll see  more on that in just a moment.

R value

The other letter was the A and this is the NPSH available. This depends on the installation of the pump and needs to be calculated. It considers things such as installation type and elevation, liquid temperature, liquid boiling point etc.

NPSHA value

The available value should be higher than the required value. (NPSHA > NPSHR)

For example if we have an installation and we calculate the NPSHA is 11 but the pump requires an NPSHR of 4 then the pump should be ok. However, if we installed a pump that required an NPSHR of 13 then the available NPSH is insufficient and cavitation will occur.

Cavitation

So what is cavitation? As we know, water can turn from a liquid state into steam or a gas state. The point at which this occurs is known as the vapour pressure. 

We know that water boils at around 100°C (212°F) and that’s because it’s at sea level which has an atmospheric pressure of 101.325 kPa (1 Bar)  but if we went to the top of Everest then water boils at just 71 °C (160 °F) because the atmospheric pressure has reduced to 34 kPa (0.34 Bar). As pressure reduces it becomes easier for water to boil.

Atmospheric Pressure

So at the suction inlet of the pump we know that there is going to be a pressure drop and if this pressure is less than the vapour pressure of the liquid being pumped then the water can reach boiling point. When that happens cavitation occurs.

During cavitation air particles within the water will expand as they reach boiling point, these will then collapse in on themselves very rapidly. As they collapse they can damage the impeller as well as the pump casing, this removes small parts of metal from the surface and if this keeps occurring then it will eventually destroy the pump. Therefore we must ensure the available pressure is higher than the required pressure of the pump.

Cavitation

Where Do We Use Centrifugal Pumps?

We use centrifugal pumps everywhere. We use them to move liquids from one tank to another or around a system.

For example we might use a small inline centrifugal pump in our domestic heating circuit to move heated water around the property.

Centrifugal pump use

We might use large centrifugal pumps to move the condenser water from a chillers condenser and up to the cooling tower on the roof as part of the centralised cooling system.

We’re going to look at the types of pumps and their applications in our next article in this series.

Privacy Overview

1.0 Purpose

Power Zone Equipment, Inc. Data Privacy Policy 

The policy set forth below outlines the personal data that Power Zone Equipment may collect, how Power Zone Equipment uses and safeguards that data, and with whom we may share it. This policy is intended to provide notice to individuals regarding personal data in an effort to be compliant with the data privacy laws and regulations of the jurisdictions in which Power Zone Equipment operates.

Power Zone Equipment encourages our employees, independent contractors, customers, suppliers, commercial visitors, business associates, and other interested parties to read this policy. By using our website or submitting personal data to Power Zone Equipment by any other means, you acknowledge that you understand and agree to be bound by this policy, and agree that Power Zone Equipment may collect, process, transfer, use and disclose your personal data as described in this policy.

2.0 Personal Data

Power Zone Equipment is committed to maintaining all reasonable precautions to ensure the privacy and security of personal data gathered by Power Zone Equipment. During your use of our website or through other communications with Power Zone Equipment, personal data may be collected and processed by Power Zone Equipment. In general, Power Zone Equipment collects personal contact information (e.g. name, company, address, telephone number and e-mail address), which you knowingly provide either by registration, requesting quotes, answering questions or otherwise for use in our commercial relationship. At times we may collect additional personal data that you voluntarily provide, including, but not limited to, job title, additional contact information, date of birth, hobbies, areas of interest, and professional affiliations.

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Power Zone Equipment’s website is intended to be used by Power Zone Equipment customers, commercial visitors, business associates, and other interested parties for business purposes. Personal data collected by Power Zone Equipment through its website or by other means is used in support of our commercial relationship with you, including, but not limited to, the processing of customer orders, orders from vendors, managing accounts, learning about customers’ needs, responding to inquiries, and providing access to information. Also, in compliance with the laws and regulations of the relevant jurisdiction to support our relationship with you:

• we may share personal data with our affiliates to better understand your business needs and how we can improve our products and services;

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If you choose not to have your personal data used to support our customer relationship (especially direct marketing or market research), we will respect your choice. We do not sell your personal data to third parties, nor share it with third parties except as set forth in this policy. Power Zone Equipment will retain your personal data as long as you maintain a customer relationship with Power Zone Equipment and/or if you have registered to receive marketing or other communication from Power Zone Equipment, until such time as you request that we delete such personal data.

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• is required by law or the competent governmental or judicial authorities;

• is necessary to establish or preserve a legal claim or defense;

• is part of a corporate restructuring, sale of assets, merger or divestiture; or,

• is necessary to prevent fraud or other illegal activities, such as willful attacks on Power Zone Equipment information technology systems.

5.0 International Data Transfer

For our customers in Switzerland and the European Union (EU), please note that Power Zone Equipment is a US based company. If you use our websites or web portals or, all information, including personal information, may be transferred to Power Zone Equipment (including subcontractors that may be maintaining and/or operating our website) in the United States and elsewhere and may be transferred to third parties that may be located anywhere in the world. Although this may include recipients of information located in countries where there may be a lower level of legal protection for your personal information than in your location country, we will protect your information in accordance with requirements applicable to your information and/or location. Specifically, for data transfers out of the EU, Power Zone Equipment will utilize data transfer agreements containing the Standard Contractual Clauses. By using our websites or web portals, you unambiguously consent to the transfer of your personal information and other information to the United States and elsewhere for the purposes and uses described herein. 

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When you access Power Zone Equipment’s websites or web portals, we may automatically (i.e., not by registration) collect non-personal data (e.g. type of Internet browser and operating system used, domain name of the website from which you came, number of visits, average time spent on the site, pages viewed). We may use this data and share it with our worldwide affiliates and related service providers to monitor the attractiveness of our websites and improve their performance or content. In this case, processing is performed on an anonymous basis and at Power Zone Equipment’s discretion.

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In addition, certain online technical applications or other interactions you have with Power Zone Equipment may require the entry of business and technical data. By providing the requested information, you are consenting to the processing and storage of such information by Power Zone Equipment. Unless Power Zone Equipment is advised that you want this information removed from Power Zone Equipment’s server, such information may be retained by Power Zone Equipment and used for future commercial communications. A request for removal of this information can be made at the contact information provided below. Power Zone Equipment will take all reasonable precautions to assure that no such information will be provided or divulged to other third parties, except, if applicable, those third parties performing site hosting, maintenance, and related site service activities.

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Power Zone Equipment will use personal data only in ways that are compatible with the purposes for which it was collected or subsequently authorized by you. While Power Zone Equipment will take reasonable steps to ensure that personal data is relevant to its intended use, accurate, complete, and current, Power Zone Equipment is also relying upon each individual to assist in providing accurate updates of his or her personal data.

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Power Zone Equipment website(s) may contain “links” to websites owned and operated by third parties. By accessing these links, which are provided for your convenience, you will leave our site and will be subject to the privacy practices of the other website. This policy does not apply to any personal information you provide to unrelated third parties.

12.0 Data Retention

In general, Power Zone Equipment will only retain personal data for as long as needed for the specific purpose of processing and in accordance with Power Zone Equipment’s records management policy, or as otherwise required by the laws and regulations of a particular jurisdiction. For example, data will be retained during the time period that you are authorized to use Power Zone Equipment website(s), including any Power Zone Equipment tools accessible through our website(s). Upon termination of such authorization, your personal data related to use of Power Zone Equipment website(s) will be removed.

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Upon request, Power Zone Equipment will grant individuals reasonable access to personal data that it holds about them. In addition, Power Zone Equipment will take reasonable steps to permit individuals to correct, amend, or delete information that is demonstrated to be inaccurate or incomplete. Power Zone Equipment also relies upon each individual to assist in providing accurate updates of his or her personal data. In order to access, correct, amend, or delete the personal data Power Zone Equipment holds about an individual, the individual should contact the following:

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If your personal data is processed in the EU or you are a resident of the EU, the EU General data Protection Regulation grants you certain rights under the law. In particular, the right to access, correct, or delete the personal data Power Zone Equipment holds about you.

To the extent required by applicable law, Power Zone Equipment will grant individuals reasonable access to personal data that Power Zone Equipment holds about them and will take reasonable steps to permit such individuals to correct, amend, or delete information that Power Zone Equipment holds about them. Power Zone Equipment also relies upon each individual to assist in providing accurate updates of his or her personal data. In order to access, correct, amend, or delete the personal data Power Zone Equipment holds about an individual, the individual should contact his or her Power Zone Equipment commercial contact or contact us at the following email address: sales@powerzone.com.  

If you have a comment, question, or complaint about how Power Zone Equipment is handling your personal data, we invite you to contact us in order to allow us to resolve the matter. In addition, individuals located in the EU may submit a complaint regarding the processing of their personal data to the EU data protection authorities (DPAs). The following link may assist you in finding the appropriate DPA: http://ec.europa.eu/justice/data-protection/bodies/authorities/index_en.htm.

15.0 Changes to this Policy

Power Zone Equipment reserves the right to modify this policy from time to time in order that it accurately reflects the legal and regulatory environment and our data collection principles. When material changes are made to this policy, Power Zone Equipment will post the revised policy on our website.

 

16.0 Questions and Comments

If you have any questions or comments about this policy (e.g. to review and update, or remove your personal data from our database) please contact +1-719-754-1981 or sales@powerzone.com