exp 7 centrifugal pump characteristics

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CE415LAppl ied Fluid Mechanics Laboratory

Experiment: No. 7 Centri fugal Pump Characteristics

Learning ObjectiveFollowing completion of this experiment and the analysis of the data, you should be able to1. describe the centrifugal pumps general operating mechanism and characteristics2. measure key parameters and plot the characteristic curves for a centrifugal pump from

the computed total head, power, and efficiency vs. flow rate3. explain what the system curve represents and how to determine the curve4. distinguish the difference between the pump total head curve and the system head curve5. identify the centrifugal pump operating point by plotting the pump total head and system

head curves together6. explain the advantage(s) of operating centrifugal pumps in series and in parallel and

identify realistic scenarios where each type should be used

IntroductionMost open-channel drainage systems rely on gravity as the force to cause water to flow.However, virtually all water distribution and parts of some sanitary and storm water systemsdepend on pumps to move the water through pipes under pressure. To impel the water to moveagainst gravity, friction and opposing pressure, pumps add energy to the fluid by performingwork on the fluid. The two main categories of pumps are positive displacement machines andturbomachines. Positive displacement machines work by changing the volume in a chamber todisplace the fluid, as with a piston-in-cylinder or helical motion. Turbomachines, on the otherhand, use rotation of blades, flow channels or passages to produce dynamic effects that addenergy to the fluid. One of the more common types of turbomachines for moving water is knownas the centrifugal pump.

In order to make the best use of your time in the lab, you will need to read through the variousparts of this document before performing the procedures and analysis. There are numeroussubtle differences between the parts of the experiment. You should also read sections 11.1through 11.4 in the textbook to gain a better understanding of the concepts to make youranalysis more productive. Note that this procedure generally uses the same variable names,symbols and terminology as used in the course textbook where possible - and so should yourreport write up and calculations.

General Procedure

Perform the distinct parts of the experiment to observe key concepts of centrifugal pumps andpipe systems. General guidelines for performing this experiment include:

a) Carefully review the equipment setup for the experiment.

b) Table 1 (on the last page of this handout) summarizes the primary parameter to becontrolled and how to do it.

c) Set the valves opened or closed as needed. You should try to visualize the fluid path insteadof simply following the words and mechanically setting the controls.

d) Because the pump drive control gradually starts and stops the pump it is not necessary tostart or stop the pump(s) with the valves shut to avoid excessive surges in the system.

e) After adjusting any valve or pump speed, wait at least 10 seconds for the system to stabilizebefore recording the instrumentation readings.

f) Re-zero pressure indicators frequently.


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g) After completing your work in the lab drain all hoses, fittings and tanks (except the mainreservoir R-1, the pumps and the piping between the tank and pumps). Remove allinterconnecting hoses and hang to let dry.

h) Clean up any water spills.

Equipment

The equipment to be used includes: SIUE Pump and Pipe Systems trainer

Digital differential pressure transducers (designated dP1 and dP2)

Timer (to measure intervals of 1 second for up to 1 hour)

Thermometer

Part 1 Centri fugal Pump Performance Curves

PurposeThe purpose of this experiment is to learn how to measure, compute and plot variouscharacteristics of a centrifugal pump. These curves are used to describe the performance

characteristics of the pump and are used to select the appropriate pump for an application.

ProceduresYour goal is to observe the performance of the pump to be tested. To do this the associatedpipe system will be reduced to the simplest arrangement possible so the pump has the leasthydraulic resistance (head) to work against.

1) Select pump 1 to be tested. Record the pump designation (Pump-1) manufacturer, modelnumber, serial number. Determine and record the suction and discharge diameters andmotor horsepower rating.

2) Set the valves to use Pump-1 isolate the other pump so that all water flow is through theselected pump. You will use the valve immediately upstream of the main flowmeter to vary

the flowrate.3) Connect a return hose, as large in diameter yet as short as possible from the outlet offlowmeter FM-1 directly to the main reservoir R-1.

4) Connect a differential pressure transducer to the inlet and discharge pressure ports at eachof the two pumps.

5) Measure the vertical distance (Hzd-Hzs) from the inlet to the discharge pressure taps for thepump under test. Zero the differential pressure transducer.

6) Set the pump drive to run the pump at 100% of maximum speed. The runtime parameters tobe displayed should be set for pump speed (in percent) and pump input power, Pi (in kW).

7) Start the pump.8) Set the flowrate control valve to fully open for the maximum (100%) flowrate.9) Record the flowrate Q, differential pump pressure head (Hp) and pump input power, Pi.

10) Using the valve following the flow meter, adjust the flow rate in increments of about 10%from 90% to 0% of the maximum flow rate. At each flowrate, record the correspondingdifferential pump pressure head and pump input power.

11) At some time during the test measure and record the reservoir water temperature (Tw) in F12) Stop the pump.

AnalysisFor this part, and for some of the following parts as required, the analysis includes computingseveral parameters and plotting the pump performance curves. A sample calculation must beprovided in your report attachment for each of the following computed parameters:


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Pump velocity head at the suction (Hvs) and discharge (Hvd) pressure tap locations (in ft)

Total pump head (H) in ft (do not ignore the elevation head)

Pump output power (Po) in Watts

Pump overall efficiency () in percent

On a single graph, labeled Experiment 7 Part1 Centrifugal Pump Performance Curves,plot the following parameters vs. flow rate Q(gpm) for the full range of flow rates tested:

Total pump head (H) in ft

Pump input power (Pi) in Watts

Pump output power (Po) in Watts

Pump overall efficiency () in percent

Include in a subtitle of the chart the watertemperature (Tw) in the reservoir in F

Note that you will need to use both the primaryand secondary y-axes (see the example at

right). Arrange the data series on the plots sothat they each cover as much of the verticalscale of the graph as possible.


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Part 2 Centrifugal Pump Performance Due to Inlet Control

PurposeThe purpose of this experiment is to attempt to find the point at which cavitation begins to occurin a centrifugal pump. This will require you to carefully listen for changes in sound coming fromthe pump, such as erratic vibrations, rattling, pulsing, pinging, etc., as the inlet flow is restrictedincrementally.

ProceduresRepeat the steps in Part 1, with the following exceptions:1) Instead of using the valve on the discharge side of the pump to control the flowrate, use the

valve on the inlet side of the pump.2) In addition to recording the same data as in Part 1, listen carefully to the sounds and

vibrations associated with the pump and note how the sound changes as the flowrate ischanged, particularly as the valve is nearly closed.

AnalysisOn a single graph, labeled Experiment 7 Part 2 Centrifugal Pump Performance Due to InletControl , plot the following parameters vs. flow rate Q (gpm) for the full range of flow rates

tested: Total pump head (H) in ft

Pump efficiency () in percent

1) Plot the characteristic curves (total head and pump efficiency all vs. volume flow rate on oneplot) as well as theHvs. Q curve from Part 1

2) On the graph, include a note to describe the sound at each point along the H vs. Q curveswhere the sound in the pump changes.

3) On the plot, annotate points on theHvs. Q curves to describe significant differencesbetween the two curves.


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Part 3 Centr ifugal Pump Performance Due to Pump Speed Control

PurposeThe purpose of this part of the experiment is to observe characteristics of a centrifugal pump asthe pump speed is varied. Varying the pump speed by controlling power input to the pump canbe an effective way to better match the pump operating characteristics to the system demandover a wider range of flow rate and system head conditions.

ProceduresRepeat the steps in Part 1, with the following exceptions:

Scenario A1) Instead of using the valve on the discharge side of the pump to control the flow rate, leave

the valve fully open, but change the pump motor drive frequency to vary the pump speed.Try to attain approximately the same flow rate points found in Part 1 by varying the pumpspeed.

2) Record the pump speedNin percent of the maximum pump speed, as well as the flow rateQ and pump input power, Pi.

Scenario B3) In a second dataset, vary the pump speed from 100% of maximum speed down to 0% in

10% increments while again measuring and recording the pump speedNin percent of themaximum pump speed, as well as the flow rate Q and pump input power, Pi.

Analysis1. On a single graph, labeled Experiment 7 Part 3 Centrifugal Pump Performance Due to

Pump Speed Control Plotted vs. Flow Rate, plot on the graph the following parametersvs. flow rate Q (gpm) for the full range of flow rates tested:

Total pump head (H) in ft from Part 1 of Exp 7

Total pump head (H) in ft from this part of the experiment

Pump input power (Pi) in Watts

Pump efficiency () in percent

Pump speed (N) in percent of the maximum speed

2. On a second graph, labeled Experiment 7 Part 3 Centrifugal Pump Performance Due toPump Speed Control Plotted vs. Pump Speed, Plot the characteristic curves (flow rate,total head, pump input power, pump output power and pump efficiency,) all vs. pump speedas a percentage of full speed.


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Part 4 System Curve and Operating Point

PurposeThe purpose of this part of the experiment is to measure the System Head Curve (head vs.flowrate) for a specific pipe system configuration and attempt to find the optimum operatingpoint for the centrifugal pump. You should note that the objective for this part of the experimentis to determine the resistance (head) presented by the pipe network (system) itself that the

pump needs to be matched to. THIS IS A VERY DIFFERENT CHARACTERISTIC YOU ARETRYING TO DETERMINE COMPARED TO THE PUMP CHARACTERISTICS EXPLORED INPREVIOUS PARTS OF THIS EXPERIMENT. The System Head Curve is determined for eachspecific water delivery system and must be known before trying to determine the pumpcharacteristics needed for the system.

ProceduresRepeat the steps in Part 1, with the following exceptions:1) Use Pump 3 which has greater capacity than pumps 1 or 2.2) Instead of trying to minimize the flow path to be as least restrictive as possible, establish the

flow through a flow path with more resistance to the flow (i.e., longer flow path or placesome restriction in the flow path to represent additional system losses.) The first

configuration set up will be called System A, the second will be System B.

3) Connect the high side of a pressure transducer to the discharge side of the pump used.Leave the low side of the pressure transducer open to the atmosphere and at about thesame elevation of the hide side connection. In this configuration the head at the high side

point is measured relative to atmospheric pressure. Only the system head vs. flow rateneeds to be observed and recorded over the range of flow rates tested.

4) Vary the flow rate from 0% to 100% in increments of 10% of the maximum flow rate byadjusting the pump speed at the pump controller panel.

5) At each flow rate increment, measure and record Q andHpressure.6) Repeat the steps above by changing the resistance in the flow path (hint: make some

adjustment to a valve or the pipe configuration.)

AnalysisOn a single graph, labeled Experiment 7 Part 4 System Curve and Operating Point, plot thefollowing parameters vs. flow rate Q (gpm) for the full range of flow rates tested:

Total pump head (H) in ft from Part 1

Pump efficiency () in percent from Part 1 System head curve (Hsystem = pressure head + elevation head) in ft vs. flow rate (Q) in gpm

from Part 4 System A

System head curve (Hsystem = pressure head + elevation head) in ft vs. flow rate (Q) in gpmfrom Part 4 System B

On the plot, annotate the point of intersection of the pump and each systemHvs. Q curve, ifthere is one, as the Operating Point along with the flowrate, head and pump efficiencycorresponding to that point.

Photograph and note the details about the portion of the system that compriseseach system. Include in your attachments a page for each system configuration thatincludes a well-annotated photograph that clearly shows the path and componentsof the system beginning at the point where the pressure head is recorded and allthe way to where the water flows back into the reservoir.


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Part 5 Operating Centrifugal Pumps in Series

PurposeThe purpose of this part of the experiment is to measure the head vs. flowrate for two centrifugalpumps operating in series to observe the resultingHvs. Q series total head curve and compareit to the characteristic total head curve for a single pump. To account for losses in the pipingconnecting the two pumps, you will measure those losses and add them to the net head gained

across the two pumps so that we can estimate the total head imparted to the water by thecombination of the series-connected pumps.

Procedures1) Configure the valves to set the flow path for the water to first go through Pump-1 followed by

Pump-2, through a flowmeter then through a large-diameter hose to return to the reservoir.2) Connect differential pressure transducers to measure the theoretical pressure head gained

as follows:

a) Using dP1, measure the net head increase (Hp_series_net) across the series combinationof both pumps. This will include the losses in the piping between them. Connect dP1(lo)to the inlet to Pump 1. Connect dP1(hi) to the discharge from Pump 2.

b) Using dP2, measure the losses (Hp_series_losses) in the piping connecting the twopumps. Connect dP2(lo) to the inlet to Pump 2. Connect dP2(hi) to the discharge fromPump 1.

3) Set the pump drives to run the pumps at 100% of maximum speed.4) Start the pumps.5) Set the flowrate control valve to fully open for the maximum (100%) flowrate. Record the

flowrateHp_series_netandHp_series_losses.6) Adjust the flowrate control valve to set the flow rate in increments of about 10%from 90% to

0% of the maximum flow rate. At each flow rate record the corresponding Hp_series_netand

Hp_series_losses.7) Stop the pumps.

AnalysisOn a single graph, labeled Experiment 7Part 5 Operating Centrifugal Pumps inSeries, plot the following parameters vs.

flow rate Q (gpm) for the full range of flowrates tested:

On the y-axis plot

Single pump pressure head (Hp) in ft fora single pump from Part 1

Series pump pressure head (Hp_series

=Hp_series_net+Hp_series_losses) in ft

On the plot, choose a flow rate at about themidpoint of the flow rate range tested anddraw a vertical line to intersect bothcapacity curves. Note the pressure headcorresponding to each of the twointersection points.


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Part 6 Operating Centri fugal Pumps in Parallel

PurposeThe purpose of this part of the experiment is to measure the head vs. flowrate for two centrifugalpumps operating in parallel to observe the resultingHvs. Q capacity curve and compare it tothe capacity curve for a single pump.

Procedures1) Configure the valves to establish parallel flow paths through Pump-1 and Pump-2, through a

flowmeter then through a large-diameter hose to return to the reservoir.2) Connect a differential pressure transducer to measure the pressure head across the parallel

pump configuration. Only the pump system head vs. flow rate needs to be observed andrecorded over the range of flow rates tested.

3) Set the pump drives to run the pumps at 100% of maximum speed.4) Start the pumps.5) Set the flowrate control valve to fully open for the maximum (100%) flowrate.

6) Record the flowrate Q and differential pump pressure head (Hp).7) Adjust the flowrate control valve to set the flow rate in increments of about 10% from 90% to

0% of the maximum flow rate. At each flow rate, record the corresponding differential pump

pressure head.8) Stop the pumps.

AnalysisOn a single graph, labeled Experiment 7 Part 6 Operating Centrifugal Pumps in Parallel, plotthe following parameters vs. flow rate Q (gpm) for the full range of flow rates tested:

On the y axis plot

Single pump pressure head (Hp) in ft for a single pump from Part 1

Parallel pump pressure head (Hp_parallel) inft (Note: There will be different losses inthe two pumps discharge pipes making itdifficult to get a true picture of the totalhead of the parallel combination. For thepurposes of this analysis compute thepressure head offset needed to adjust thepressure head of the parallel combinationto equal the pressure head of the singlepump at the shutoff head value. Thenadjust all of the computed pressure headvalues for the parallel pumps by that offsetvalue.)

On the plot, choose a pump pressurehead at about the midpoint of the flow raterange tested and draw a horizontal line tointersect both capacity curves. Note theflowrate and pressure head values ateach of the two intersection points.


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Table 1 - Primary parameter to be controlled and how to do itPart Set Target By Adjusting Comments

1

Flow rate, Q, from100% to 0% relativeto Qmax in 10%increments.

Valve immediately downstreamof the flowmeter

2Flow rate, Q, from100% to 0% relativeto Qmax in 10%increments.

Valve immediately upstream ofpump inlet

3-A

Flow rate, Q, toapproximatelyachieve the flowrates from Part 1.

Electronic drive frequency atcontroller to vary the pumpspeed.

3-BPump speed, N, in10% incrementsrelative to Nmax.

Electronic drive frequency atcontroller to vary the pumpspeed.

4

Flow rate, Q, from100% to 0% relative

to Qmax in 10%increments.

Electronic drive frequency atcontroller to vary the pump

speed.(shown as a percentageof maximum pump speed)

You probably will not be able to observemeasurable flow at lower pump speeds.

The best approach is to start atmaximum flow rate then decrease pumpspeed toward N=0%.

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exp 7 centrifugal pump characteristics

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