The affinity law for fans and dynamic pumps, 2692018 duration. The pump speed needs to be reduced in order to achieve the required flow at the twl and the required speed can be calculated using the affinity laws. A prototype pump is made from a model by multiplying all dimensions of the model by the same factor. Centrifugal pump affinity laws provide a method to determine a new pump operating point when a performance curve that indicates performance with different impeller diameters or operating speeds is not available. The diameter of the pump impeller is reduced when the pump speed is constant. May 01, 2017 the affinity laws, also known as pump laws, for pumps are used to express the relationship between variables involved in pump performance such as head, flow rate, shaft speed and power. Other pump formulas affinity laws changes in diameter changes in speed d diameter, in or mm q flow, gpm or m3h h head, ft or m p power, hp or kw. Leave a comment if you would like to discuss the affinity laws or variable frequency drives.
N speedrpm the affinity law for a centrifugal pump with the impeller diameter held constant and the speed changed. The affinity laws, also known as pump laws, for pumps are used to express the relationship between variables involved in pump performance such as head, flow rate, shaft speed and power. Example pump affinity laws changing impeller diameter. In the united states, electricity is at 60 cycles per second hertz. Often times a fans speed or impeller diameter will be changed. The affinity laws tell you how a centrifugal pump responds to changes in conditions see section 4. Jul 20, 2016 the centrifugal pump affinity laws, sometimes known as the laws of similarity, describe how changes in rpm affect the gpm, head, and hp.
Pump efficiency is considered as a constant and variation in speed and impeller diameter is analyzed for the variation in above said parameters. Affinity laws for pumps and fans affinity laws are used to relate the performance of a pump or fan from a known operating condition to a new, unknown condition. If you know the shape of a pump performance curve at a certain speed or with a certain impeller diameter. The affinity laws are useful as they allow prediction of the head discharge characteristic of a pump or fan from a known characteristic measured at a different speed or impeller diameter. You can quickly determine the effect of changes in either pump speed or impeller diameter on pump performance. Most pumps need minimum flow protection to protect them against shutoff. This method is referred to as the affinity laws or fan and pump laws.
Pump affinity laws are equations of proportionality that indicate how a change. The course content is in a pdf file 467 kb basic pump parameters and the affinity laws. The affinity laws for centrifugal pumps and fans are used to express the influence on volume capacity, head pressure andor power consumption due to. The performance of a given pump at various speeds and the performance of geometrically similar pumps is governed by a set of formulas known as the affinity laws. Pdf evaluating the approximation of the affinity laws and.
If the fan is a centrifugal fan, then the change in performance of the fan can be predicted quickly through the affinity laws. If the performance of a given model pump is known, the performance of a prototype pump can be predicted. Affinity laws and specific speed in centrifugal pumps. If you know the shape of a pump performance curve at a certain speed or with a certain impeller diameter, you can use the affinity laws to predict the. Usually, pump performance curves are based on standard electric motor speeds in rpm. The affinity laws for centrifugal pumps state that the hq curves at various rotational speeds can be derived from the following relationship as conventionally represented. Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps with changing speed or wheel diameters. Q flow rate h head y specific energy n rotational speed if pq.
Horwitz project engineer affinity laws the performance of a given pump at various speeds and the performance of geometrically similar pumps is governed by a set of formulas known as the. The affinity laws describe how changes in rpm n affect gpm, head, and hp in centrifugal pumps. I told him to send me his pump curve and system curve with the next email to explore this option. Aug 14, 2014 the affinity laws below are well known and used daily by pump people. The affinity laws for centrifugal pumps state that the hq curves at various rotational speeds can be derived from the following relationship as conventionally represented q flow rate h head y specific energy n rotational speed. Nov 24, 2016 centrifugal pump affinity laws are set of mathematical equations correlating the flow rate, head, brake horse power, speed and impeller diameter of the pump. The pump capacity, or flow rate, q varies with the ratio of rpm. Care must be taken to correctly read the performance data from pump curves.
Part 2 pump operating modes, affinity laws, speed, and head series pump installation analysis 6. The process of arriving at the affinity laws assumes that the two operating points that are being compared are at the same efficiency. Another set of the affinity laws deal with changes to the diameter of the impeller. To approximate the performance of the pump, the affinity laws should be used as follows. In general, the affinity laws project the new operating points by. The pump speed, head, and flow relationships are expressed by the affinity laws.
When a fan operates in an unchanging system, the fan laws tell us that the airflow varies proportionally to fan rpm, static. Engineers use a shorthand for estimating the effect of speed rpm on power. The affinity laws allow engineers to estimate the resulting changes to certain hydraulic parameters caused by the manipulation of a single centrifugal pump variable. The performance of a given pump at various speeds and the performance of geometrically similar pumps is. Peerless pump company indianapolis in, 462077026 technical. How the affinity laws affect pump rerates turbomachinery. The same principles govern both, the idealized affinity laws for centrifugal pumps cp, and the friction drops for systems on newtonian fluids.
The affinity laws also known as the fan laws or pump laws for pumps fans are used in hydraulics, hydronics andor hvac to express the relationship between variables involved in pump or fan performance such as head, volumetric flow rate, shaft speed and power. Horwitz project engineer affinity laws the performance of a given pump at various speeds and the performance of geometrically similar pumps is governed by a set of formulas known. There are occasions when you might want to permanently change the amount of fluid youre pumping, or change the discharge head of a centrifugal pump. If you double the speed of the pump then you double the flow. You may occasionally need to estimate the hydraulic performance of a centrifugal pump at a speed or impeller diameter not shown on the catalog performance curves. The affinity laws for pumpsfans are used in hydraulics, hydronics andor hvac to express the. Q1 q2 n1n2 x d1d2 h1 h2 n1n22 x d1d22 p1 p2 n1n23 x d1d23 npsh31 npsh32 n1n22 per standard nomenclature, q is flow rate, h is head, p is power, and npsh3 is net positive suction head for a 3 percent head drop. They were only recalled upon exporting a pump to a. The affinity laws variable frequency drives theory the affinity laws can determine the system performance for centrifugal devices, including theoretical load requirements and potential energy savings. Until a few years ago, the affinity laws were on the back burner and mostly ignored. Using affinity laws, we can accurately calculate the pressure, flow and required speed and power of a pump from a specific known set point. In this case, the prototype pump and the model are said to be homologous to each other. Pump affinity laws are equations of proportionality that indicate how a change in impeller diameter d, or rotative speed n, affects the capacity q, the differential head h, and the required brake horsepower hp of a centrifugal pump.
Pump affinity laws example for centrifugal pumps as per the pump manufacture the specifications for that pump given as flow rate q 100 m 3 hr, head 70 metres, rpm 1440, pump input power bhp 21 kw and its impeller dia 240mm. Or to put it another way, the affinity laws for a centrifugal pump do not and are not supposed to be dependent on duty. In the case of homologous pumps, the affinity laws state. Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps with changing speed or wheel. The relationship between two operating points, say 1 and 2, depends on the shape of the system curve see figure 420. The analysis is based on the reduced impeller being geometrically similar and operated at dynamically similar conditions or equal.
The affinity laws for centrifugal pumps describe the impact of changes in speed or impeller diameter on pump flow, head, and hp. Centrifugal pump affinity laws are set of mathematical equations correlating the flow rate, head, brake horse power, speed and impeller diameter of the pump. For example, if rpm drops to 70% of the original, gpm drops to 70% of the original. The maximum break horsepower bhp would then be determined using the drivers efficiency.
The affinity laws are used to express the relationship between variables involved in pump. The affinity laws can be calculated at a single point or charts of flow rate, head, and power can be plotted against changes in impeller speed or diameter. They are merely a way of predicting the charcteristic curve of the pump when you have a known characteristic curve and wish to make a variation in speed of the pump or diameter of the impeller. May 07, 2016 this video screencast was created with doceri on an ipad. The centrifugal pump affinity laws, sometimes known as the laws of similarity, describe how changes in rpm affect the gpm, head, and hp in the united states, electricity is at 60 cycles per second hertz. Todays eitpe exam question looks at the pump laws with with a constant diameter impeller. The only requirement is that the two pumps or fans are dynamically similar, that is the ratios of the fluid forced are the same. They apply to all types of centrifugal and axial flow pumps. The affinity laws also govern the performance of geometrically similar pumps.
The affinity laws express the mathematical relationship between the several variables involved in pump performance. Affinity fan and pump laws what is the effect of a changing speed. The affinity laws, or formulas, state that for a given pump, the capacity. Pdf evaluating the approximation of the affinity laws. If the speed should remain a constant, the affinity laws state. Hvac equipment and systems fan affinity laws for the. In these rotary implements, the affinity laws apply both to. This page provides information and resources regarding the affinity laws that are used to project new performance points and curves for a pump or fan given a known performance point or curve. Affinity laws can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed. Using characteristic pump parameters such as the impeller diameter d, rotational speed n, acceleration due to gravity g and the density of the fluid handled.
Variable speed photovoltaic water pumping using affinity laws. The affinity laws are a set of forumlas that predict the impact of a change in rotational speed or impeller diameter on the head and flow produced by a pump and power demanded by a pump. As for the square law for pumps and the relation between h and q on flow systems one sees that both can be. These laws are mathematical expressions that define changes in pump brake horsepower bhp, head and capacity when a change is made to pump speed, impeller diameter, or both. The relationships established between the physical quantity of the original and that of the model by means of the characteristic coefficients are called affinity laws.
Pump engineering calculations of brake horsepower, power, kilowatts, motor, motors, voltage drop, circular mills, transformers, turns ratio, ohms law, dc power. To the affinity laws and beyond the affinity laws below are well known and used daily by pump people. The affinity laws of centrifugal pumps or fans indicates the influence on volume capacity, head pressure andor power consumption of a pump or fan due to. Pump curve speed calculator affinity law calculator. Q1 q2 n1n2 x d1d2 h1 h2 n1n22 x d1d22 p1 p2 n1n23 x d1d23 npsh31 npsh32 n1n22 per standard nomenclature, q is flow rate, h is head, p is power, and npsh3 is net positive suction head for a 3% head drop. The affinity laws below are well known and used daily by pump people. The affinity laws are a group of laws and rules that govern your pumps. The following websites offer excellent additional information on pumps and hydraulic systems.
What is the resulting change to the pump speed and horsepower needed. This would deliver less flow and conserve some power. For a change in impeller diameter with the rotational speed held constant, the following performance. Centrifugal pump affinity laws calculation chemical. This centrifugal pump curve calculator is meant to quickly calculate the different operating conditions when a centrifugal pump is sped up or slowed down. Alps cannot handle the complication of a control valve in the pump s discharge line. Pump affinity laws for centrifugal and positive displacement. Represented in figure 3 are the three affinity laws. A 25 horsepower and 3600 rpm b 15 horsepower and 1450 rpm c 60 horsepower and 2900 rpm d 15 horsepower and 2900 rpm. Affinity laws relate to the characteristics of pumps operating at different speeds, and in a water distribution context, are usually used to predict the pump curve of variable speed pumps vsps. Affinity laws the affinity laws are derived from a dimensionless analysis of three important parameters that describe pump performance. All you need to know is the system head and flow requirements to determine the right pump for the job. The energy savings are achievable through affinity laws.
Pdf affinity laws relate to the characteristics of pumps operating at different speeds, and in a water distribution context, are usually used to. Affinity laws the affinity laws can be used to predict pump performance if the impeller size or rotational speed is changed. Using the affinity laws, it is possible to determine approximate curves to estimate the centrifugal pump s new best efficiency point. The affinity laws are derived from a dimensionless analysis of three important parameters that describe pump performance. The speed of a pump is measured by how many revolutions per minute rpms are completed by the spinning impeller. Centrifugal pump fundamentals pumps are broadly classified as kinetic or positive displacement. In practical application, grundfos provides all the information you need to easily determine your energy savings with e pumps and boosterpaqs. The good news affinity law theory helps us understand the principle of flow, head, and power dynamics. Law 1 means that as rpm is reduced, flow gpm is reduced in a linear relationship. The affinity laws or fan laws, as they are sometimes referred to play an important role in determining centrifugal pump performance when operating conditions change. If you know the shape of a pump performance curve at. Affinity laws for pumps and fans vortarus technologies llc. Basic pump parameters and the affinity laws a pdh online. White paper stop falling off the curve maintenance.
Friction a b hs h o figure 3 conclusion of our look at a new tool that predicts how pumps and systems interact. According to the affinity laws, the following relationships exist between the actual speed of the centrifugal pump and its most important performance. Flow is directly proportional to the speed of the of the pump in revolutionsmin. Hello everyone, i am sizing a pump and ran into a question of how to apply the affinity laws and interpret their results. The affinity laws for centrifugal pumps state that the hq curves at various rotational speeds can be derived from the following relationship as. In practical application, grundfos provides all the information you need to easily determine your energy savings with epumps and boosterpaqs. The affinity laws allow engineers to estimate the resulting changes to certain hydraulic parameters caused by the manipulation of a single centrifugal pump. The pump head pressure varies with the square of the change in the speed. First affinity law flow is proportional to the shaft speed, i. If a more detailed analysis is required, you should graphically analyze the pump and systems curves. Using the affinity laws, it is possible to determine approximate curves to estimate the centrifugal pumps new best efficiency point. If a centrifugal pump is driven by an ac driver, then it should operate at a fixed rate rpms dictated by the frequency of the supplied power. Pump curve speed calculator this centrifugal pump curve calculator is meant to quickly calculate the different operating conditions when a centrifugal pump is sped up or slowed down.
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