Pump Chart Basics Explained - Pump curve HVACR

hey there guys Paul here from the engineering mindset calm in this video we're going to be looking at pump curves to learn how to read them on what the different lines mean after you've learned about pump performance curves and the part they play in pump selection visit today's sponsor stay supply.com to find the right pump for your curve requirements shop for parts or speak to a knowledgeable pump expert on top brands like Belen Gossett tacko and more so click the link in the video description below to find out more the basic pump curve looks like this but they do get more complicated and looks something like this don't worry we're going to go through them step by step and start from the basics each type of pump has a different chart and the data plotted on them also varies with the model the first thing we notice is that on the main vertical y-axis we have the head pressure and on the vertical x-axis we have the flow rate basically speaking the head is pressure and the flow rate is how much water the pump can move so what do these charts represent if we turn the pump sideways and connected it to a pipe the pump is pushing the liquid horizontally so there is no pressure but the water is flowing at its maximum flow rate as we slowly rotate the pump towards the vertical position we see the flow rate decreases but the pressure increases that's because it's now pushing against the water and the friction as we get all the way to the vertical position there is zero water flowing out of the pump but maximum pressure and that's because it's using all its energy to push against the water and hold it as high as it possibly can within the pipe at this point is just spinning the same bit of water which isn't good for the pump so you don't want to run a pump like this in the real world by recording the values during the elevation we basically get our pump curve although I will note the pump manufacturers don't test pumps this way because it's just not practical if you want to know how a centrifugal pump works then we have covered this in detail in our previous video do you check that out links down below Hale is shown on the vertical axis and this is referring to pressure so we often hear the term head pressure we measure head in feet or meters which doesn't seem correct considering we're talking about pressure especially as you see the pressure gauges on the pump typically reading psi or bar the reason for feet or meters is that pump manufacturers only know how high their pump can push a liquid they do not know which liquid your system will be pumping and as easily grid has different properties the pressure will vary depending on the liquid used however the hightly can be moved by the pump will remain the same for example we have this pump which can provide 125 feet of head if we use it to pump water the pressure will be around 50 4.25 PSI but if we were to use it to pump milk then the pressure will be around 50 6.15 psi and that's purely because of the properties of the two fluids conversion between feet and meters of head is very easy we have a freak out player for that because you can find links to in the video description below why do we need to know head pressure pumps are usually used to move liquid to a higher region so we need to ensure the pump can reach this elevation as we pump liquid through the pipes and the fittings friction will try to oppose the flow this occurs from the walls of the pipe but also disturbances to the flow path this causes pressure losses which wastes energy from the pump the amount of friction depends on the liquid type as well as the materials and fittings used therefore we must calculate how much friction or pressure loss our system will generate and ensure that the pump we select can overcome this otherwise we're not going to get any liquid out the upper end when we look at the pump charts will find pumps ranging in head and flow rate for example when we look at a small domestic heating system there are a few fittings and short pipes therefore we would use a pump with a relatively low head pressure but if we were to look at a commercial heating system with multiple air handling units fan coils and long pipe lengths then we know the pressure drop will be much higher so we will need a pump that can provide much more head pressure the flow rate is a measurement of how much liquid is flowing from the pump in a given amount of time this measurement comes in many different units for example gallons per minute leases per second or cubic meters per hour for example a system might be designed to move 2 litres of water per second from a holding tank to a process tank once curve this is sometimes refer to as the HQ Co H meaning head and cube which represents flow rate the manufacturer will test each pump to obtain the performance data and then plot this on the graph this will represent all the possible configurations between flow rate and head pressure and we use this to check whether our pump will suit our requirements the performance curve will be different for each pump and some will suit our system these better than others you will usually see that as the pump flow rate increases the head pressure decreases when selecting a circulating pump the pump will only perform as per the line so for this model if we wanted eight gallons per minute then we would have six-foot of head you can also get multi-speed circulating pumps which we'll look at later on in this video when selecting a larger centrifugal pump as long as our system requirements are on or below the performance line then the pump can be considered we can potentially use a smaller impeller or variable frequency drive to better suit or requirements and again we're going to look at that a little later in this video for example the performance curve of two large centrifugal pumps are plotted here we need a flow rate of 30 gallons per minute and a head pressure of 70 feet that means that pump 2 can't be used but pump 1 could be impeller size with centrifugal pumps we can often change the size of the impeller the diameter of the impeller will change how much water can be moved so on some charts you'll see multiple performance curves which will give us the performance details of the pump for different diameter impellers for example 30 gallons per minute for a 4.5 inch impeller gives us around 13 feet of head but if we use the 5.5 inch impeller then we would get around 20 2.5 feet of head in some instances our required flow rate and head pressure up might fall between the two impeller diameter lines in such cases we can often machine the impeller down to the required size to get a better match you should ask your pump manufacturer or pump specialist to carry out this service though the performance of the pump will then need to be calculated I'll leave some links in the video description below for worked examples for that pump power as we know pumps require mechanical power to spin the shaft rotor and ultimately move the water pump manufacturers will usually provide a chart which plots the power requirement in imperial units we use brake horsepower and in the metric system we use kilowatts with this chart we see the brake horsepower plotted at various intervals as you can see as the flow rate increases so does the power requirement we use this chart to size our motor for example if we needed 125 gallons per minute with 18 feet of head then this is between the 0.75 and the one horsepower lines as this point is above the 0.75 line this means we can't use a motor of this rating because it will not be able to cope therefore we'll have to use a 1 brake horsepower motor and we see the performance curve Falls completely under this line so if our head pressure calculation is wrong then we do have some safety margin if you want to convert between brake horsepower and kilowatts then check out our free calculator links down below for that efficiency some charts will display the efficiency curve of the pump this is measured in percent we will usually see this curve line where the pump increases up to its maximum efficiency and then it starts to decline again charts that display different impeller sizes will usually have efficiency displayed in these more complex plot lines each line displays the percentage of efficiency in both charts you can see that the efficiency varies depending on how you operate the pump in multiple impeller size charts we see that the efficiency decreases as the impeller size also decreases and that's because the gap between the impeller and the pump casing increases and that will allow water to resurvey in this region and therefore waste energy the efficiency is the ratio or comparison between the amount of energy going into the pump versus the amount of energy we get out of the pump so ideally we want this to be as close as possible to the peak for optimal performance the pump will always lose some power when it converts and transmits this electrical energy into mechanical energy and this will be lost through the couplings the bearings the shaft the seals the cooling fan etc for example on this chart we can see that if the pump provided 125 gallons per minute at 25 feet of head then it would run at around 67% efficiency which isn't very good if the same pump operated at 30 feet of head for 138 gallons per minute then it would operate at its peak performance of 73 percent which is much better mps H this is the required MPs H or net positive suction head pressure the usually has an upward curve which means as the pump flow rate increases we see the MPs H value also increases we measure this in meters or feet sometimes kiloPascals the MPs H is the minimum pressure that must be available of the suction inlet of the pump to overcome the entrance losses and avoid cavitation the available pressure at the inlet must therefore be greater than this value pump cavitation is where the pressure at the inlet of the pump reaches a low enough point that the water begins to boil this creates rapidly expanding and collapsing air bubbles which will gradually destroy the surface of the pump and the casing for this example if we were to move 150 gallons per minute then we would require an MPs H value of around four point nine feet multi speed pumps some pumps such as this one operate at a fixed speed and therefore have a fixed performance curve but we can also get multi speed versions which have the ability to switch between speed settings typically these come with three different speeds low medium and high these pumps will therefore have a chart with three different profiles plotted on them we can operate the pump at any of these curves but not between them so for this example if we wanted six gallons per minute or 0.3 liters per second then on setting one we would get around 4.2 feet of head-on setting - we will get eight feet and on setting three would get around nine point eight feet variable speed or variable frequency drives another option we have is to use a variable frequency or otherwise known as a variable speed drive this basically takes the electrical supply and alters it to reduce the voltage and frequency which therefore alters the power of the motor and the speed of the pump we can increase or decrease the speed via the controller to better improve our pump match and therefore operate nearly anywhere in the region below the curve these are only really used on larger pumps typically over two kilowatts in size they do come pre-installed with new pump motors or you can also retrofit existing pumps you should check with the manufacturer first to ensure compatibility additionally you must check the system design to ensure it can handle a lower flow rate and head pressure obtain the performance details for variable speed pumps we have to calculate the values using the pump affinity laws we've covered this previously in worked examples links down below for that rotational speed sum pump manufacturers will provide separate charts for operating the pump at different rotational speeds we can then compare the performance to get a close match and then find an electrical motor which will suit our needs typically speaking higher rotational speeds lead to more service and maintenance so where possible is good practice to choose a lower speed pump that meets our system requirements voltage and frequency do check the specifications of the electrical motor the voltage and frequency for mains electricity vary around the world so we want to ensure that the pump you select will operate where you are installing it additionally pumps come in single as well as at three-phase designs depending on the application these details will be provided by the manufacturer and usually come on the chart or a technical document okay guys that's it for this video but to continue your 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 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Keywords: pump chart, pump curve, npsh, process engineering, fluid mechanics, pressure drop, centrifugal pump, efficiency, pump head, cavitation, mechanical engineering, how to read a pump curve, mechanical energy, pipe flow, hvac, hvac technician, technician, hvac school, hvacr, how does a centrifugal pump work, impeller, hvac basics, pump, priming, centrifugal, hvac training videos, elearning, industrial engineering, hvac system, head pressure, maintenance, e-learning, hvac course, flow rate

Id: U8iWNaDuUek

Length: 13min 5sec (785 seconds)

Published: Sun Mar 08 2020