Shadowing Practice: Centrifugal Pump Basics - How centrifugal pumps work working principle hvacr - Learn English Speaking with Video
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Hey there guys, Paul here from TheEngineeringMindset .com.
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In this video, we're going to be looking at centrifugal pumps to learn the basics of how they work, the different types and where we use them.
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You can get more information on centrifugal pumps, shop for parts and accessories or talk to experts on top pump brands like Bell & Gossett,
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Taco and more by visiting Statesupplier .com who have kindly sponsored this video.
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Simply click on the link in the video description down below to find out more.
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Centrifugal pumps come in many shapes, colors, and sizes, but they typically look something like this.
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The pumps consist of two main parts, the pump and the motor.
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The motor is an electrical induction motor, which allows us to convert electrical energy into mechanical energy.
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This mechanical energy is used to drive the pump and move the water.
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The pump pulls water in through the inlet
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and pushes it out through the outlet as we take the unit apart we can see
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that we have a fan
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and a protective casing mounted at the back of the electrical
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motor then inside the motor we have the stator the stator holds the copper coils
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and we're going to look in detail at that a little later in this video
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concentric to this we have the rotor and shaft the rotor rotates
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and as it rotates so does the shaft the shaft runs the entire length from the motor and into to the pump.
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This then connects into the pump's impeller.
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Some models of centrifugal pumps, like this one, will have a separate shaft for the pump and the motor.
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Separated shafts are joined using a connection known as a coupling.
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Coupled pumps will usually have a bearing house which, as the name suggests, houses the bearings.
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The shaft continues into the pump casing.
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As it enters the casing, it passes through a gland, packing, and the stuffing box, which combine to form a seal.
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The shaft then connects onto the impeller.
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The impeller imparts centrifugal force onto the fluid which enables us to move liquids, such as water, through a pipe.
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The impeller is enclosed within the pump casing.
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The casing contains and directs the flow of water as the impeller pulls it in and pushes it out.
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Therefore, we have a suction inlet and a discharge outlet.
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At the back of the electrical motor, we see that the fan is connected to the shaft.
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When the motor rotates the shaft, the fan will therefore also rotate.
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The fan is used to cool down the electrical motor
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and it will blow ambient air over the casing to dissipate the unwanted heat.
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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.
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The fins on the outside perimeter of the casing increase the surface area of the casing
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which allows us to remove more unwanted heat.
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The electrical motor comes in either three phase or single phase configuration depending on the application.
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We're going to look at three phase as this is the most common.
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Inside the three phase induction motor, we have three separated coils which are wound around the stator.
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Each coil set is connected to a different phase to produce a rotating magnetic field.
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When we pass AC or alternating current through each coil, the coil will produce an electromagnetic field
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which changes in intensity as well as polarity as the electrons passing through it change direction between forwards and backwards.
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But if we connect each coil to a different phase then the electrons will change direction between forwards
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and backwards at a different time compared to the other phases.
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This means
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that the magnetic field of each coil will change in intensity
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as well as polarity at a different time compared to the other phases.
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To distribute this magnetic field we rotate the coils 120 degrees from the previous phase
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and insert them into the stator of the motor casing.
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This will create the effect of a rotating magnetic field.
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At the center of the stator we place the rotor and shaft.
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The rotor will be affected by the rotating magnetic field and will force it to also rotate.
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The rotor is connected to the shaft
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and the shaft runs from the fan through the rotor all the way up to the impeller.
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This way when the rotor rotates so will the impeller.
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So now by creating the rotating magnetic field within the motor we spin the rotor
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which spins the shaft and this spins the impeller.
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Looking at the pump casing we find a channel for water to flow along which is called the volute.
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This volute spirals around the perimeter of the casing up to the pump outlet.
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This channel increases in diameter as it makes its way to the outlet.
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The shaft passes through the seals and into the pump casing where it connects to the impeller.
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There are many types of impeller, but most will have these backward curved vanes which will either be open, semi -open, or closed with some shrouds.
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These backward curved vanes do not push the water.
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The curves rotate with the outer edge moving in the direction of the expanding volute.
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These vanes will provide the fluid with a smooth path for the water to flow.
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We'll see that a little later in this video.
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The impeller is submerged in water.
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When the impeller rotates, the water within the impeller also rotates.
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As the water rotates, the liquid is radially pushed out in all directions to the edge of the impeller
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and into the volute.
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As the water moves outwards off the impeller, it creates a region of low pressure which pulls more water in through the suction inlet.
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The water enters into the eye of the impeller and it's trapped there between the blades.
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As the impeller rotates, it imparts kinetic energy or velocity onto the water.
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By the time the water reaches the edge of the impeller, it has reached a very high velocity.
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This high speed water flows off the impeller and into the volute, where it hits the wall of the pump casing.
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This impact converts the velocity into potential energy or pressure.
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More water follows behind this and so a flow develops.
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The volute channel has an expanding diameter as it spirals around the circumference of the pump casing.
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As it expands, the velocity of the water will decrease, resulting in pressure increasing.
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This expanding channel therefore allows more water to keep joining and converting into pressure.
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So the discharge outlet is therefore a higher pressure than the suction inlet.
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The high pressure at the discharge allows us to force the fluid through pipes
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and into a storage tank or around a pipe system.
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The thickness of the impeller and the rotational speed affects the volume flow rate from the pump.
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But the diameter of the impeller and the rotational speed will increase the pressure it can produce.
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Centrifugal pumps are represented in engineering drawings with symbols like these.
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They can vary slightly from this, so do check the drawings information section.
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NPSH A term you're going to hear is the NPSH, which is the acronym for Net Positive Suction Pressure.
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We'll briefly cover what this means.
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There are two letters at the end of the acronym, the NPSHR and the NPSHA.
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The R is the required NPSH.
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Each pump is tested for this value, and this can be obtained from the pump manufacturer by the pump's operating chart.
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Don't worry about this confusing looking chart at this point, we're going to break it down and cover that in detail in a dedicated video.
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Links to that in the video description down below.
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The R value is basically a warning or danger point.
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As the water enters the pump and flows into the impeller's eye, it experiences a lot of energy due to the friction.
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This will give us a pressure drop.
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at certain conditions the water flowing through this section can reach boiling point
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when this occurs we refer to this as cavitation we're going to see more on that in just a moment
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the other letter was the a
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and this is the mpsh available this depends on the insulation of the pump
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and needs to be calculated it considers things such as insulation type
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and elevation liquid temperature liquid boiling point etc the available pressure should always be higher than the required value.
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For example if we have an insulation
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and we calculate the NPSH A as 11
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but the pump requires an NPSH R of 4 then the pump should be okay.
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However if we installed a pump
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that required an NPSH R of 13 then the available NPSH is insufficient and cavitation will occur.
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So what is cavitation?
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As we know water can turn from a liquid state into steam or a gas state.
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We know that water boils at around 100 degrees Celsius
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and that's because it's at sea level which has an atmospheric pressure of 101 .325 kPa.
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But if we went to the top of Mount Everest then water boils here at just 71 degrees Celsius
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and that's because the atmospheric pressure has reduced to 34 kPa.
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As the atmospheric pressure reduces it becomes easier for the water to boil.
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So at the suction inlet of the pump we know
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that there is going to be a pressure drop and
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if this pressure is less than the vapor pressure of the liquid being pumped then the water can reach boiling point.
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When this happens cavitation occurs.
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During cavitation air particles within the water will expand as they reach boiling point.
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These will then collapse in on themselves very rapidly.
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As they collapse they will damage the impeller as well as the pump casing.
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This remove small parts of metal from the surface and if this keeps occurring then it will eventually destroy the pump.
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Therefore we must ensure the available pressure is higher than the required pressure of the pump.
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We use centrifugal pumps everywhere.
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We use them to move liquids from one tank to another or around a system. For example,
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we might use a small in -line centrifugal pump in our domestic heating circuit to move heated water around the property.
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We might use a large centrifugal pump to move the condenser water from a chiller's condenser
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and up to the cooling tower on the roof as part of the centralized cooling system.
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We're going to look at the type of pumps and their application in our next video in this series.
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Okay, that's it for this video, but to continue your learning then check out one of the videos on screen now
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and I'll catch you there for the next lesson.
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Don't forget to follow us on Facebook, Twitter, Instagram as well as
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Who Is This Video For?
This video is perfect for English learners at an intermediate level who want to boost their technical vocabulary and practice listening to clear, conversational explanations. Whether you’re into engineering or just curious about how things work, it’s a great way to learn real-world English while exploring centrifugal pumps. The slow, deliberate speech makes it ideal for shadowing technique practice—you can easily repeat phrases and mimic the rhythm as you learn.
Words & Idioms Worth Stealing
- Imparts centrifugal force: Gives a spinning force to something. Example: "The blender imparts centrifugal force to mix the ingredients."
- Dissipate heat: Spread out or remove heat. Example: "A fan helps dissipate heat from a laptop."
- Short circuit: A fault in an electrical system causing a sudden surge. Example: "Water damaged the phone, leading to a short circuit."
- Concentric: Having the same center. Example: "The target has concentric circles."
How to Get the Accent Right
The speaker uses a clear, neutral English accent with a focus on stressing key technical terms. To practice, try shadow speech by pausing the video after short phrases (like "convert electrical energy into mechanical energy") and repeating them aloud. Pay attention to how he emphasizes words like "impeller" and "stator"—the stress is on the first syllable. For extra practice, use a shadowing app to record yourself and compare it to the video. You can also find a shadowing site to connect with other learners. Remember, the goal is to match the rhythm and clarity, not just the words. Learn English with videos like this one, and you’ll build confidence in both technical and everyday speech!
Grammar in this video
The structures the speaker uses most, with the exact words from the video:
| Structure | In the video |
|---|---|
| Passive voice be + past participle — the focus is on what happens, not who does it | are joined · is enclosed · is connected |
| Relative clauses who / which + clause — extra information about a person or thing | coils which are · along which is · vanes which will |
| Present perfect have/has + past participle — a past action that still matters now | has reached · has reduced |
What is the Shadowing Technique?
Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.