Centrifugal Pump Basics - How centrifugal pumps work working principle hvacr

[Applause] hey there guys Paul here from the engineering mindset calm 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 you can get more information on centrifugal pumps shop for parts and accessories or talk to experts on top pump brands like Belen Gossett taco and more by visiting state supplier comm who have kindly sponsored this video simply click on the link in the video description down below to find out more centrifugal pumps come in many shapes colors and sizes but they typically look something like this 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 holds water in through the internet and pushes it out through the outlet as we take the unit apart we can see that we have a fan and a protective casing mounted at the back of the electrical motor then inside the motor we have the stator the stator 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 the entire length from the motor and into the pump this thing connects into 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 couple pumps will usually have a bearing house which as the name suggests houses the bearings the shaft continues into the pump casing enters the casing it passes through a gland packing and the stuffing box which combined to form a seal the shaft then connects onto the impeller the impeller imparts 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 fire water as the impeller pulls it in and pushes it out therefore we have a suction in that and a discharged outlet 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 increased the surface area of the casing which allows us to remove more unwanted heat 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 this is the most common inside the three-phase induction motor we have three separated coils which are wound around the stator each coil set is connected to a different phase to produce a rotating magnetic field 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 but if we connect each coil to a different phase then the electrons will change direction between forwards and backwards at a different time compared to the other phases this means that the magnetic field of each coil will change in intensity as well as polarity at a different time compared to the other 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 center 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 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 its way to the outlet the shaft passes through the seals and into the pump casing or it connects to the impeller 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 these backward 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 flow we'll see that a little later in this video the impeller is submerged in water when the impeller rotates the water within the impeller also rotates as the water rotates the liquid is radially pushed out in all directions to the edge of the impeller and into the balloon as the water moves outwards off the impeller it creates a region of low pressure which pulls more water in through the suction Inlet the water enters into the eye of the impeller and is trapped there between the blades 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 blue 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 our 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 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 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 centrifugal pumps are represented in engineering drawings with symbols like these they can vary slightly from this so do check the drawings information section in psh a term you're going to hear is the NP s H which is the acronym for net positive suction pressure will briefly cover what this means there are two letters at the end of the acronym the NP s HR and the NP SH a the R is the required MPs H each pump is tested for this value and this can be obtained from the pump manufacturer by the pump operating chart 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 links to that in the video description down below the r-value is basically a warning or danger point as the water enters the pump and flows into the impellers eye it experiences a lot of energy due to the friction this will give 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're going to see more on that in just a moment the other letter was the a and this is the MPs H available this depends on the insulation of the pump needs to be calculated it considers things such as insulation type and elevation liquid temperature liquid boiling point etc the available pressure should always be higher than the required value for example if we have an insulation and we calculate the MPs H a is 11 but the pump requires an MPs HR of 4 then the pomp should be okay however if we installed a pump that required an MPs HR of 13 then the available MPs H is insufficient and cavitation will occur so what is cavitation as we know water can turn from a liquid state into steam or gas state we know that water boils at around 100 degrees Celsius and that's because is at sea level which has an atmospheric pressure of 101.325 kpa but if we went to the top of Mount Everest then water boils here at just 71 degrees Celsius and that's because the atmospheric pressure has reduced to 34 kPa as the atmospheric pressure reduces it becomes easier for the water to boil so with 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 vapor pressure of the liquid being pumped then the water can reach boiling point when this 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 will 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 insure the available pressure is higher than the required pressure of the pump we use centrifugal pumps everywhere we use them to move liquids from one tank to another or around the system for example we might use a small in-line centrifugal pump in our domestic heating circuit to move heated water around the property we might use a large centrifugal pump to move the condenser water from a chillers condenser and up to the cooling tower on the roof as part of the centralized cooling system we're going to look at the type of pumps and their application in our next video in this series okay that's it for this video but to continual learning then check out one of the videos on screen now and I'll catch you there for the next lesson don't forget to follow us on Facebook Twitter Instagram as well as the engineering mindset calm

Channel: The Engineering Mindset

Views: 1,345,273

Keywords: centrifugal pump, cavitation, priming, npsh, centrifugal, how does a centrifugal pump work, impeller, elearning, hvac, hvacr, hvac technician, technician, hvac school, pump, Centrifugal Pump, Enclosed impeller, Home water pump, Semi open impeller, turbomachinery, water pump, Open impller, Impeller, Sealing of pump, Pump (Invention), digital learning, maintenance, fluid mechanics, mechanical engineering, hvac basics, chiller, air handling unit, hvac training videos, condenser, hvac course, ac

Id: XpcCUtYzwy0

Length: 10min 35sec (635 seconds)

Published: Sun Mar 01 2020