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. If the rotational speed is doubled, flow is also doubled. In the case of positive displacement pumps the affinity laws are very straight forward. Increasing flow increasing head parallel pumps if both pumps are operating at the same speed and one fails, the operating point shifts down the system curve to the point where the single pump curve crosses it. Knowing the effects of varying a centrifugal pumps speed is helpful in many situations, such as. Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps with changing speed or wheel. The affinity laws, or formulas, state that for a given pump, the capacity. Pump affinity laws and how to apply known data to pump curves will be discussed and demonstrated.
Shashi menon, in transmission pipeline calculations and simulations manual, 2015. All you need to know is the system head and flow requirements to determine the right pump for the job. The pump speed is changed when the impeller size is constant. The affinity laws for fans and pumps provide a way of determining new fan or pump speed given fan or pump performance curve data and a desired operating point combination of flow rate and pressure that does not fall on the curve. The affinity laws show that the pump head decreases significantly when the pump speed is reduced to match system flow requirements see figure. Pump affinity laws or pump laws are used during hydraulic design to calculate the volume, capacity, head, or power consumption of the centrifugal pumps with changing speed or wheel. Centrifugal pump affinity laws calculation chemical. Centrifugal pumps are commonly used in industrial and urban. 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. The only requirement is that the two pumps or fans are dynamically similar, that is the ratios of the fluid forced are the same. Affinity laws affinity laws are the performance of centrifugal pumps based on change in speed, power, flow, head, impeller diameter. Various configurations of air systems such as supply. Affinity law for multistage pumps pump engineering engtips. In particular, the approximation inherent in the affinity law that computes power and efficiency.
The affinity laws for pumpsfans are used in hydraulics to express the relationship between variables involved. Pump laws pump laws are used in hydraulics, hydronics andor hvac to express the relationship between variables involved in pump or fan performance such as head, volumetric. This centrifugal pump curve calculator is meant to quickly calculate the different operating conditions when a centrifugal pump is sped up or slowed down. Doc introduction to affinity laws ahmed elhalfawy academia. Pump shaft horsepower requirements vary as the product of head and flow or as the cube of the pump s speed ratio. Aug 14, 2014 the affinity laws below are well known and used daily by pump people. Pump systems analysis 7 a system with three singlespeed pumps. I am not aware of any pump affinity laws regarding multiple stages.
One can trim an existing impeller and the affinity laws will apply to the new conditions. The affinity laws allow engineers to estimate the resulting changes to certain hydraulic parameters caused by the manipulation of a single centrifugal pump variable. Preservation of efficiency affinity revisited pumps. In general, the affinity laws project the new operating points by moving up and down a system curve. Pump affinity laws for a specific centrifugal pump. Hydraulically the major subjects consist of head, capacity, hydraulic efficiency, power, and speed. Yet the modified affinity laws produce a single common curve for all operating conditions and viscosities for a specific pump. Pdf evaluating the approximation of the affinity laws and. Until a few years ago, the affinity laws were on the back burner and mostly ignored. Affinity laws the affinity laws can be used to predict pump performance if the impeller size or rotational speed is changed. This affinity law allows you to project the power required by a given impeller.
Download a complete calculation example in pdf format. Process engineers lock onto this law as a means to control the flow of process. Note, however, that the affinity laws will not provide accurate. The affinity laws can be used to determine the rotational speed at any desired operating point. Pump affinity laws with a sample calculation what is piping. White paper stop falling off the curve maintenance. Download 707k power point download 177k pdf version download 92k pdf script. Q flow rate h head y specific energy n rotational speed if pq.
These laws are essentially the same as the affinity law for speed change but do not apply with the same. P 1 p 2 n 1 n 2 3 or d 1 d 2 3 where p is equal to power, n is equal to shaft speed, and d is equal to impeller diameter. The affinity laws for pumpsfans are used in hydraulics, hydronics andor hvac to express the. Centrifugal pump fundamentals pumps are broadly classified as kinetic or positive displacement. According to the affinity laws, the 6in impeller should produce a bep flow of 466gpm at a head of 111ft.
Head by the square cs current speed pumps brisbane pump. This video screencast was created with doceri on an ipad. Centrifugal pump affinity laws calculation chemical engineering. Also shown is the range of operating points between minimum and maximum static lift for a single pump. Pump designers have needed a way to compare the efficiency of their. My current view is the original 10stage pump would be 96ft per stage. Pump curve speed calculator affinity law calculator inventory. The initial flow is 100 gpm, the initial head is 100 ft, the initial power is 5 bhp, the initial speed is 1750 rpm and the final speed 3500 rpm. Note that there are two sets of affinity laws affinity laws for a specific centrifugal pump to approximate head, capacity. This means that if the affinity law calculations were based on required head and. They are used to predict what effect speed or impeller diameter changes have on centrifugal pump performance. One can trim an existing impeller and the affinity laws.
Affinity laws are also known as affinity equations. Pdf centrifugal pump head prediction using affinity laws. Pdf beware the affinity police arsalan aslam academia. Using affinity laws, we can accurately calculate the pressure, flow and required speed and power of a pump from a specific known set point. The affinity laws are obeyed, which means that there is a substantial reduction in power absorbed accompanying the reduction in flow and head, making variable speed the ideal control method. Vector control is used to control the vsi fed three phase induction motor driving the water pump. For example, if you reduce the pump speed from 3,450 rpm to 2,400 rpm 30% reduction in speed the wattage drops from 2,000 watts to 593 watts 70% reduction in power.
Pump affinity laws the fundamental fluid mechanic relationships developed thus far can be modified to generate other useful relations between pump fan parameters. With regard to total performance and efficient design, these two. Pump selection, sizing and troubleshooting, kolmetz handbook of process equipment design. 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. The affinity laws express the mathematical relationships between the several variables involved in pump performance. Pdf evaluating the approximation of the affinity laws. Pump curve speed calculator affinity law calculator. 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. Its free and a wonderful resource for the industry and you can download it at. Affinity laws for impellers trimmed in two partial emission pumps with. Is it a radial type pump which provides high head and low flow or an axial. Pdf a new approach based on the similitude principle is used to evaluate the effect of fluid viscosity on pump performance. 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 affinity laws.
This is a complete example using a real system which will take the reader through all the steps required to calculate the total head of a pump, the n. There is a number called the specific speed of a pump whose value tells us something about the type of pump. These relationships are known as pump fan affinity laws. Impeller diameter change an overview sciencedirect topics. Page 1 of 4 affinity laws for variable speed centrifugal pumps jayanthi vijay sarathy, m. The affinity laws for centrifugal pumps are used to predict pump performance for changes in. Centrifugal pumps have a rotating impeller, also known as a blade. The modified affinity laws accurately models the performance dependence upon viscosity. The good news affinity law theory helps us understand the principle of flow, head, and power dynamics. Affinity laws online excel calculator is available for download. Variable speed photovoltaic water pumping using affinity laws. Centrifugal pump specific speed primer and the affinity laws jacques chaurette p. Affinity laws the affinity laws are derived from a dimensionless analysis of three important parameters that describe pump performance.
Enter information as instructed below and press calculate. Peerless pump company indianapolis in, 462077026 technical. Note that the affinity laws for speed change are exact. Aug, 2014 to the affinity laws and beyond the affinity laws below are well known and used daily by pump people. In practical application, grundfos provides all the information you need to easily determine your energy savings with e pumps and boosterpaqs. In the paper, such affinity laws in terms of constant and variable exponents were established for flow rate, head, efficiency, flow coefficient and.
The affinity laws can be used to predict pump performance if the impeller. 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. Affinity although we tend to associate affinity laws with centrifugal pumps, other mechanical devices also exhibit these natural relationships. If the system pump is flowing x gpm at y feet of head and we want to double the flow rate. 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. 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.
Centrifugal pump affinity law is explained for speed change and impeller. Estimation of power consumption by centrifugal pump. Affinity law for multistage pumps pump engineering. How the affinity laws affect pump rerates turbomachinery. The engineer in 1977 estimated the 7stage pump to be 440ft at shutoff. We finish with a discussion of suction conditions and liquid friction. Part 2 pump operating modes, affinity laws, speed, and head. Pdf affinity laws relate to the characteristics of pumps operating at different speeds, and in a water distribution. As with the standard affinity laws, a pumps functional relationship varies with each pump design. The pump vendor must be consulted to verify that the predicted values using affinity laws for impeller size changes are accurate or if any correction factors are needed. Today i field verified the shutoff being with 10% of 440ft. Effect of change of speed or impeller diameter on centrifugal pumps. The mathematical relationships that exist between flow rate, head, power and speed and based on a known pump performance are referred to as the affinity laws. In a positive displacement pump, npsh varies as a function of flow determined by speed.
Volume capacity the volume capacity of a centrifugal pump can be expressed like q1 q2 n1 n2 d1 d2 where q volume flow capacity m3s, gpm, cfm, n wheel velocity revolution per minute rpm d wheel diameter head or pressure the head or pressure of a centrifugal pump can be expressed like dp1 dp2 n1 n22 d1. The affinity laws state changes in the speed or diameter change capacity by direct proportion. The operating point of the pump, relative to its best efficiency point, remains constant and the pump continues to operate in its ideal region. Application of the affinity laws to predict the impact of changes in speed can produce highly accurate results. The pump affinity laws are basically a set of formulas that predict the impact of change in pump impeller diameter and its rotational speed on the pump head h, pump flow q, and power demand of the pump p.
Estimation of the efficiency for variable speed pumps in. It says, the change in pump head or pressure drop in the system varies as the square of the change in gpm flow rate. Parallel pumps if both pumps are operating at the same speed and one fails, the operating. The analysis is based on the reduced impeller being geometrically similar and operated at dynamically similar conditions or equal. However, the affinity law calculations require using a point on the curve. Gpm gallonsminute rpm revolutionsminute p pressure, psi hd ft. Aug 29, 2019 affinity laws for variable speed centrifugal pumps 1.
The pump performance data from published literature 2 was utilized to further evaluate the modified affinity laws. The affinity laws for pumps fans are used in hydraulics andor hvac to express the relationship between variables involved in pump or fan performance and pow. This means that if the affinity law calculations were based on required head. Analytical solution for speed to achieve a desired.
Reducing the speed of the positive displacement pump, reduces the npsh affinity laws the turbo machine affinity laws are common used for pumps and fans to calculate. Pump engineering calculations of brake horsepower, power, kilowatts, motor, motors, voltage drop, circular mills, transformers, turns ratio, ohms law, dc power. They were only recalled upon exporting a pump to a country with different electricity. In a centrifugal pump, npsh varies as a function of flow determined by pressure 2. In these rotary implements, the affinity laws apply both to centrifugal and. Page is color controlled with prinect color editor 4. Home usace technical letters index turbine affinity laws. The predictions are only slightly better for the 7in impeller but come pretty close in the case of the 8in trim because its efficiency, at 75%, is nearly that of the full size. The affinity laws are a group of laws and rules that govern your pumps. You can quickly determine the effect of changes in either pump speed or impeller diameter on pump performance. Evaluating the approximation of the affinity laws and improving the.
Basic pump parameters and the affinity laws pdh online. Development of modified affinity law for centrifugal pump to. Centrifugal pump fundamentals pumps are broadly classified as. However, the affinity laws for impeller diameter change are only approximate and valid for small changes in impeller sizes. 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. Individual pumping systems as well as open systems, closed systems, pumps in series and pumps in parallel and npsh requirements will be covered.
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