e TQ Education and Training lid 2000 No part of this publicationmay be reproduced or transmittedin any form or by any means,electronicor mechanical, including photocopy, recording or any information storageand retrieval system without the expresspermission of TQ Education and TrainingUmited. All due care has been taken to ensure that the contents of this manualare accurate and up to date. However, if any errorsare discovered please inform TQ so the problemmay be rectified. A Packing Contents List is supplied with the equipment. Carefully checkthe contentsof the package(s) against the list. If any itemsare missing or damaged, contact your local TQ agent or TQ immediately. TQ Education and Training Ltd Products Division PWF/PE/O199
Transcript
e TQ Education and Training lid 2000No part of this publication may be reproduced or transmitted inany form or by any means, electronic or mechanical, includingphotocopy, recording or any information storage and retrievalsystem without the express permission of TQ Education andTraining Umited.
All due care has been taken to ensure that the contents of thismanual are accurate and up to date. However, if any errors arediscovered please inform TQ so the problem may be rectified.
A Packing Contents List is supplied with the equipment.Carefully check the contents of the package(s) against the list. Ifany items are missing or damaged, contact your local TQ agentor TQ immediately.
TQ Education and Training Ltd
Products DivisionPWF/PE/O199
TECQUIPMENT H32 SERIES AND PARALLEL PUMP TEST SET
CONTENTSPAGESECI'ION
Safety and Operation Information
Introduction 11.0
Simple Theory of Pump Performance 22.0
12Description of Apparatus
Installation 16
18Experiments
21Typical Results
31APPENDIXl Loss Coefficients
Typical Experimental Results 33APPENDIX 2
READ AND UNDERSTAND THE FOllOWING INFORMATION BEFORE INSTALLING AND OPERATING THIS APPARATUS.
KEEP THIS INFORMATION FOR FUTURE REFERENCE.- - --
SAFETY AND OPERATION INFORMATION
Product: H32 Series and Parallel Pump Test Set
NOTE ~ A protective coating may havebeen applied to parts of thisapparatus to prevent corrosionduring transport. Remove thecoating with paraffin or whitespirit, and a cloth or brush.
Symbols may be used in this manual to attract theoperator's attention to specific information. Thesesymbols and their meanings are as follows:
Visually inspect all pipes, flanges, glands, covers,casings, seals and instrumentation for transit damage.
Drain the Hydraulic Bench and remove theHydraulic Bench top. Loosen the clip which secures thesump outlet pipe. Feed the pipe through the fibre glassmoulding.
Position the H32 Series and Para1Iel Pump Test Setclose to the Hydraulic Bench. Connect the H32 inlet tothe sump outlet pipe. Ensure that the pipe is not kinkedor otherwise obstructed which would restrict the waterflow.
Connect a gate valve to the outlet of the H32 unit.Connect a return pipe from the gate valve and insert thefree end through the top of the Hydraulic Bench into themeasurement tank. Ensure that the pipe is long enoughnot to kink when in use. Check all clips are in place andtight
Check the electrical supply required for the H32from the plate close to the lead outlet.
Always isolate the apparatusfrom the electrical supplybefore accessing any electricalcomponents.
Always comply with anystatutory requirements that arein force about the installation,operation and maintenance ofthis apparatus in the countrywhere it is to be used.Students using this apparatusmust be supervised. WARNING ~
Foreseen Use of ApparatusProvides the means to study the characteristics of twosimilar single-phase multi-speed pumps working ontheir own, or connected in series or in parallel. It is foruse with a TQ Hydraulics Bench (HI or HId).
The electrical supply providedfor this apparatus must beconnected to the apparatusthrough a switch, circuit-breaker or plug and socketcombination so the apparatuscan be isolated from the supplywhen needed.The apparatus must beconnected to earth.
Risks due to Wrong UseElecbic shock or damage to the apparatus if theelecbical connection is not completed correctly, or theapparatus is operated with covers removed.
NOTE ~Electrical connections must be madeas follows:
Installation and Assembly InstructionsThe 'Packing Contents List' that is supplied with diisapparatus is a list of items that are provided with theapparatus to enable normal use of it during die warrantyperiod. If any item is missing or damaged, contactTecQuipment Limited or the in1porter.
To fit a connector suitable for local supply needs,follow the instructions supplied with the connectorusing the following colour code for the supply cable:
GREEN-AND-YELLOW: EARm (E or~)BROWN: LIVE (L)BLUE: NEUTRAL (N)
NOTE ~ WARNING ~Elecbical coMcctions must bemade to a supply capable ofproviding a minimum of 5 A at230 Va.c.
Electrical maintenance mustonly be carried out by acompetent person.
Periodically inspect the apparatus to ensure there is novisible damage. Pay particular attention to connectors,switches, indicators, and cables. Also inspect pumps,pipes, flanges, glands, covers, casings and seals forleaks.
If the apparatus does not work correctly, contactTecQuipment Limited or the importer for advice.
Handling InstructionsNet weights 25 kg
Fill the Hydraulic Bench with clean water. Make surethat the bench controls are set so that water returns tothe sump.
Bleed the pump to remove any b'apped air using thebleed plug on the pump. Check that the pump motorrotates freely by inserting a small screwdriver into theend of the shaft, push gently and turn.
Switch on the unit and check that the systemfunctions correctly with no leaks. To ensure that thereis no trapped air in the pipes and valves, tilt the wholepump apparatus so that the outlet pipe is higher than theinlet Run the unit with the valves set as shown inFigure I , and run at maximum speed for a few minutes.Switch off and prepare for an experiment.
WARNING ~Ensure that the correctprocedures for handling thisweight are used when movingthis apparatus.
Operating Conditions
Figure 1
Operating InstructionsThe apparatus must be used within its operating limits(refer to the section titled Operating Conditions).
CAUTION ~Do not run the pumps unlessthe apparatus is connected to asuitable water supply.
Ensure the voltage on the serial number label attachedto the apparatus is the same as the local electrical supply
voltage.
Set the valves for a particular pump test (refer to main
manual).Set the required pump speed. Switch on the unit by
depressing the switch on the console. Set up thedelivery flow rate by adjusting the gate valve on theoutlet side of the pumps.
Noise LevelThe maximum sound pressure levels measured for thisapparatus when operating at maximum level are lessthan 70 dB.
Maintenance and Inspection~ Do not attempt to disassemble
CAUTION the pumps, as it may cause
damage to the apparatus.
Spare PartsRefer to the 'Packing Contents List' for any spareparts that are supplied with the apparatus.
Contact TecQuipment Limited or the importer if anyother spare parts are needed.Ensure the water used contains no dirt or grit.
If the apparatus will not be used for a long period,isolate it from the electrical supply and dry all the partsas far as possible.
If the pumps have been inoperative for a longperiod, check the pump shafts for free rotation beforeswitching on.
TECQUIPMENT H32 SERIPS AND P ARALLBL PUMP TEST SBT
1.0 INTRODUCTION
Pumps are used to transfer fluid in a system, either at the same level or to anew height. The flow rate depends on the height to which the fluid ispumped, and the relationship between "head" and flow rate is called the"pump characteristic". This has to be determined experimentally for a pumpand the TecQuipment H32 Series and Parallel Pump Test set provides a lowcost and effective way of demonstrating how this is achieved, and enablingmore detailed experiments to be done.
The H32 uses domestic central heating pumps, more correctly known asHcirculators", which provide relatively low outputs compared with pumpsdesigned for high performance. This enables the HI Hydraulic Bench to beused as both the source of water and to measure the flow rate.
Often in civil engineering applications a single pump cannot deliver the flowrate or head necessary for a particular need, and two (or more in practice) canbe combined in series to increase the height to which the fluid can bepumped, or in parallel to increase the flow rate. The H32 demonstrates howthe combined pump characteristic compares with that of the single pump.
More sophisticated pump test sets, such as the H36 Computerised CentrifugalPump Test Rig, may be found in the TeCQuipment range. These are suitablefor more advanced studies in the fluid dynamic performance of pumps.
TBCQUIP~ ~2 ~~ AND ~~ LLBL PUMP TFsr SET
2.0 SIMPLE THEORY OF PUMP PERFORMANCE
The increase in head H between the inlet and outlet of a pump is a function ofthe flow rate Q and rotational speed N. This relationship is expressed
graphically and called the "pwnp characteristic", as shown in Figure 1.
~"tStU
::!:
N3
Increasing speed
Flowrate (Q)
Figure 1. Pump characteristics.
~ead" (H) is a height measured in metres of water, but an alternativeconvention is to use the pressure rise across the pump, I1p (N/m2or bar)
Ap and H are related to each other by
Ap = pg H
In terms of Head:-
Mass flow rate through pump, m=pQ (kg/s)
TBCQUIPMBNT H32 SERIES AND P ARALLBL PUMP TFSr SET
Hydraulic power generated,
~ = mgH = pgQH (W)
Electrical power input to pump = w
Overall pump efficiency
..e~~w
~1\= W .In terms of pressure rise across the pump:-
Q~p11=W-
The overall efficiency of a small circulating pump is typically not muchgreater than 10 to 15%.
Some text books work in terms of Ap, others in terms of H. The two sets ofequations look similar, but differ by the presence of pg. Never confuse the
two systems!
The H32 pump manufacturer's published performance curves are shown in
Figure 2.
For practical convenience, pressure is measured in kN/m2 and flow rate inlitres/sec, but on the experimental equipment the pressure is measured inbars (1 bar = lOOkN/ml
If you are using a gravimetric hydraulic bench, approximately for water,
1litre/sec = 1 x 10-3 m3 Is ~ 1 kg/s
The input power W I may be measured on a wattmeter or the ~pmanufacturers published data may be used.
TBCQUIPMBNT H32 SBRIBS AND P ARALLBL PUMP TPST SET
60Selectric
1 X 240V 50Hz
50
40
30-~~
20
10
00.2 0:40 0:6 0.8 1.0 12
U tres / sec
Figure 2. Manufacturer's published performance curves.
Two pumps in series
A schematic representation of two pumps in series is shown in Figure 3.Ignoring any losses that occur between the two pumps, the flow rate throughboth is the same, but the overall pressure rise is the sum of the two individualvalues. If both pumps are identical then the pressure rise is doubled for agiven flow rate. Figure 4 shows the pressure-flow characteristics for twopumps in series.
TBCQUIPMENT H32 SERIPS AND PARALLEL PUMP TPST SET
14 Aij ~r No los~ f APt .1
~
Figure 3. Schematic showing two pumps in series.
~
Q
Figure 4. Pressure-Flow characteristics for two pwnps in series.
TBCQUD'MENT H32 SBRIBS AND P ARALLBL PUMP TEST SET
Two pumps in parallel
ApL_~_- ~
r'~~
c ~I
~ '."AIl
L_~rc;-
\.6.p,
Figure 5. Schematic showing two pumps in parallel.
A scltematic representation of two pwnps in parallel is shown in Figure 5.I~oring any losses between the two pumps, the pressure rise across eachpwnp is the same, and is the total pressure rise. The overall flow rate is thesum of the two individual values, as shown in Figure 6. If both pumps areidentical, then the total flow rate is twice that of each single pump.
TECQUIPMENT H32 SERIFS AND P ARALLBL PUMP TEST SET- - -- -
~ Q
Figure 6. Pressure-Flow characteristics for two pumps in parallel.
The actual pressure - flow characteristic is a curve of the form;.2
~p=A-BQwhere A and B are constants which depend on the system. It is thereforeuseful to plot curves of ~p against 02 (Figure 7), which should be straightlines.
Ap
Figure 7. Curves of Ap against 02.
TECQUIPMBNT H32 SBRIBS AND P ARALLBL PUMP TPSf SET
In practice, due to manufacturing tolerances the performance of each singlepump may be slightly different. For demonstration purposes, it is satisfactoryto assume that both pumps have the same characteristic. The experimentalresults shown in Section 6 confirm this.
Bernoulli's equation is used to estimate the inlet pressure to the pump.
vtIIIIIIIIII
b==:==~
Pour
0131
'Will- .
I=---:=~~-~~---\--- (i;:::::::~.
--~~~~I
::::::::~"'t'~Control
valveHydraulic benchI
hA ~
Datum(floor)
Figure 8. Schematic ()f apparatus
0 POUT, {/'IPIN, 'T~
--l-~--Ah,I , ~
I
r
Figure 8a. Detail of pump.
TP.CQUIPMENT H32 SBRIFS AND P ARALLBL PUMP TEST SET
Referring to Figures S and Sa, find the difference in levels between the waterin the reservoir and the pump inlet, L1h.
It may be convenient to use the floor as a datum, so that
L\h = hA - he
The pressure at the pump inlet is
PIN = pgAh-1:K 1IJ.pV2 (gauge)
Where I.K (see Figure 9) is the sum of all the dynamic pressure lossesbetween the water level in the reservoir and the pump inlet, and V is thespeed of water in the pipe.
Pipework K varies between1 and 1.2 for all configurations
/ I
'\.K~O.5 max
Figure 9 Pressure losses K, within the pipe.
For convenience, an approximate total value of LK = 1.5 will be assumed forthe pipework for all pump configurations. Note that the flow control valvemust be placed after the pump(s) to eliminate its unknown variable pressuredrop from the equation.
= 9810 Ah - 750y2Hence: PIN
7td2 V4
Since Q=AV=
andd = 22mm
Then to the same accuracy of reading of the Bourdon gauge
TBCQUIPMBNT H32 SERIES AND PARALLEL PUMP TEST SET
Mt .PIN ~w - .O625Q
(PIN is measured in bar (gauge), Ah in metres and Q in litres or kg per second)
Including the pressure drop, due to friction, in the inlet pipe, the followingare suggested:-
very short pipe
Ah-10
- 0.125 Q21 metre pipe PIN =
Ah10
- 0.18 Q22 metre pipe PIN =
It is difficult to obtain an exact calibration since the flow changes fromlaminar to turbulent as the flow control valve is adjusted. For demonstrationpurposes, rather than for absolute accuracy, it is convenient to set up thewater level the same (approximately) as the pump inlet. The dynamic losscan be ignored, especially at low flow rates, so that the inlet pressure isapproximately zero (gauge). The pressure rise across the pump is then equalto the reading of the pump outlet gauge.
It is left to the reader to make a more accurate prediction if required.coefficients are given in Appendix I.
Knowing the height difference between the reservoir level and the pumpinlet, and the measured flow rate, the pump inlet pressure can be calculated.The pressure rise across the pump is Pour- PIN. If PIN is negative, then the twonumbers effectively add.
Pump efficiency
Pump efficiency is calculated from :-
QApTl;~
TECQUIPMENT H32 SERIES AND PARALLEL PUMP TEST SET
Where Q is the flow through each pump and ~p is the pressure rise across it.
Care should be taken when calculating the individual efficiency of pumps inseries and parallel.
In series, the flow through each pump is equal to the measured flow, but thepressure rise across the upstream pump is approximately (PI - pJ.
For parallel flow the flowrate through each pump is half the measured value.
TECQUIPMBNT H32 SERIES AND PARALLEL PUMP TPST SET
3.0 DESCRIPTION OFAPP ARATUS
Figure 10 The H32 Series and Parallel Pump Test Set (view from above
showing control panel and pump layout).
The TecQuipment H32 Series and Parallel Pump Test Set, shown in Figure 10,is one of a range of small equipment intended for use with the TecQuipmentHI Gravimetric Hydraulic Bench or Hld Volumetric Hydraulic Bench.
Two similar single phase multi-speed pump units are connected by a pipe
system so that each pump can be run on its own, combined in series, orcombined in parallel. Figures lla, b, c, and d show the position of the threevalves A, B and C required to set up each flow condition.
Each pump has a concrol panel which enables it to be switched on or off,
together with a three speed conh"ol.
Details of the pump construction and maintenance required is given in the
manufacturers Data Sheet (supplied separately).
TBCQUIPMBNT H32 SERIES AND P ARALLBL PUMP TPST SET
-4--~ 4
0$0$@ \~~;:~:~
~Figure lla. Setting the three control valves: Pump 2 only.
@0 \~~~~S
0$$0
(:::~:::) ~ .
Figure llb. Setting the three control valves: Pwnp 1 only.
TBCQUlPMBNT H32 SERIFS AND PARALLEL PUMP TFST SET
.--T'@
0 \~~~:s
0$1
0 \~~~:~-(~) "4
Figure llc. Setting the three control valves: Pumps in parallel.
0$
Figure lId. Setting the three control valves: Pumps in series.
TECQUIPMBNT H32 SERIFS AND PARALLEL PUMP TEST SET
A single Bourdon gauge is fitted to the top panel which can be switched tomeasure the delivery pressure of either pump. The pump inlet pressure canbe determined from Bernoulli's Equation. The water flow rate is adjustedusing a gate valve fitted in the rehlm pipe between the pump test set and thehydraulic bench. This valve must not be fitted in the water pipe leading tothe pump test set, as to do so would mean that an unknown and variablepressure drop would be introduced so that the pump inlet pressure could notbe determined. If a valve is fitted before the pump, it must be fully openwhen measurements are taken. For experiments to determine the pumpoverall efficiency, it is necessary to measure the input electrical power with awattmeter. However, the input powers quoted by the pump manufacturerwill be sufficient to demonstrate how the efficiency is calculated. Table 1gives typical input powers and pump speeds, but actual values should beobtained from the manufacturers data sheet (supplied).
~~12
':: '3
Revs/ ~Input power, watts40
70
105
750
1150
1850
Table 1 Typical pump input powers and speeds.
mCQUIPMENT H32 SBRIPS AND PARALLEL PUMP TEST SET
4.0 INSTALLAnON
1) Drain the H1 Ot'H1d Hydraulic Bench.
2) Remove the Hydraulic Bench top.
3) Loosen the clip which secures the sump outlet pipe. Feed the pipe throughthe fibre glass moulding.
4) Position the H32 Series and Parallel Pump Test Set close to the HydraulicBench.
5) Connect the H32 inlet to the sump outlet pipe. A gate valve could be fittedto the H32 inlet if desired, but must always be open fully when takingmeasurements. Ensure that the pipe does not kink, resbicting the waterflow.
6) Connect a gate valve to the outlet of the H32 unit.
7) COlU\ect a return pipe from the gate valve and insert the free end throughthe top of the Hydraulic Bench into the measurement tank. Ensure that thepipe is long enough not to kink when in use. Note that if the pipe is kinkedwhen in use it will affect the water flow rate and consistency of results. Ifnecessary support the pipe or use reiriforced pipe.
8) Check all clips are in place and tight.
9) Check the elechical supply required for the H32 from the plate close to thelead outlet. Connect to a suitable supply. This MUST be earthed. DONOT START THE PUMP YET.
10) Fill the Hydraulic Bench with clean water. Make sure that the benchcontrols are set so that water returns to the sump.
11) SOmetimes air can be trapped inside the pump, which will then notfunction correctly. Bleed the pump to remove any trapped air using the
bleed plug on the pump.
TBCQUIPMBNT H32 SERIFS AND P ARALLF.L PUMP TESI SET
12) Check that the pump motor rotates freely by inserting a smallscrewdriver into the end of the shaft, push gently and turn.
13) Set up one of the pipe configurations using valves A, B and C. Switch onthe unit and check that the system functions correctly with no leaks. Toensure that there is no trapped air in the pipes and valves, tilt the wholepump apparatus so that the outlet pipe is higher than the inlet. Run theunit with the valves set to parallel flow, and run at maximum speed for afew minutes. Any trapped air will soon be dispersed.
14) Switch off and prepare for an experiment.
TBCQUIPMBNT H32 SBRIBS AND P ARALLBL PUMP TEST SET- - -
5.0 EXPERIMENTS
The following experiments may be performed using the TecQuipment H32Series and Parallel Pump Test Set
1. Performance of Pump 1 at a fixed speed
n. Performance of Pump 2 at the same fixed speed.
ill. Performance of a single pump, range of 3 speeds.
iv. Performance of two pumps in series, fixed speed
v. Performance of two pumps in series, different speeds.
vi. Performance of two pumps in parallel, fixed speed.
vii. Performance of two pumps in parallel, different speeds.
Note that the speeds of each pump when operating in either series or parallelare normally the same (for example both 750 rpm). However, there is noreason why the pumps should not be run at different individual speeds.
TBCQUIPMBNT H32 SER1PS AND P ARALLBL PUMP TPSr SET
Procedure
(a) Set the valves for a particular pwnp test (refer to Figure 11 if
necessary).
(b) Set the required pump speed(s)
(c) Switch on the unit by depressing the green button on the coI1SOle.
(d) Set up the delivery flow rate by adjustment of the gate valve on theoutlet side of the pumps. It is convenient to start with a fully openvalve. Measure the flo~ rate using the Hydraulic Bench (refer to therelevant hydraulic bench manual for details of flow measurement).
(e) Read the delivery pressure of each pump by switching to either Pt orpz- Ensure the valve is switched off after each measurement.
(f) Enter the results in the table.
Repeat for several different flow rates until the control valve is fullyclosed.
(g)
(h) Measure the difference in height between the water surface in thereservoir and the pwnp inlet. Calculate the inlet pressure.
(i) Calculate the pressure rise across the pum,p.*
Plot a graph of pressure rise against flow rate or (flowrate)2.(j)
(k) If required, calculate and plot the overall efficiency of the pump
system
* Note for demonstrati()J1 purposes, steps (h) and (i) can be ignored providing the waterleVel in the hydraulic bend1 is about the same height as the pump inlet. ill this case p~ = 0
TECQUIPMENT H32 SERIFS AND PARALLEL PUMP TEST SET
Mt= .~
Operation ~~.e;le/Series/Paralle!Puma Saeed 750/1150/1800 revs/min.Time(sec) t
pour{l)bar
pour{2)bar
Apbar
'1%PIN
barQt -2Q
Pump electrical power oW,
- Cross out inapplicable condition..
t TIme to collect x kg or litres of water ..
* Either litres / sec or kg/sec.
If single operation, state whether pump 1 or pwnp 2 was used.
TBCQUIPMENT H32 SERIES AND PARALLEL PUMP TEST SET
6.0 TYPICAL RESULTS
This section shows results obtained from a TecQuipment H32 Series andParallel Pump Test Set, as described in this manual.
Tests were conducted according to the procedures given previously in themanual. As a result of manufacturing and test condition variations,characteristics of individual units may differ from these specimen results, andtherefore they must be interpreted as a general guide only.
More data obtained from actual experimentation and presented in table formis given in Appendix 2.
Single pump
Collect 15 kg water,
Ooeration :>mQ;le pump 1
Puma speed 1800 revs/min, 10SW.2
QTime p~t(l)bar
Tt%
Qkg/sset
Valve closed1106641312320
00.140.230.370.480.650.75
00.020.050.130.230.430.56
0.54
0.50
0.48
0.41
0.34
0.22
0.15
06.49
10.39
14.29
15.67
14.29
10.71
Notes
(I)
(2),
(3)
Pump inlet at same level as hydraulic benchMinor losses igI':"oredAp across pump approximately equal to Pout
TECQUIPMENT H32 SERIFS AND PARALLEL PUMP TPST SET
Figure 12 shows the performance of single pumps at the three power settings,and pumps in series at 105W.
1.1..[ Single
x pump 1+ pump 21.0
~Series
0.9-
0 pump 10 pump 20.8-
0.7
:a.Q0..
0.6-
0.5 ~ 'X °
0.4
~,0 CS'~
~.~ ~ Q(A
~<i- ~~. 0
~~
~~t.~~
~~.~8~ ~+ x ~/e A 0 ~~. 0 ~8~4"'."", . ~ ",--.f! Cls-~ ~ ..1;;.. ,
Pll41 "':-.. ~~ 0 y~tp (?O~""". ~. Y.J "~~~~S .
~ e. (~Wj
'
0.3-
.. x.~,
b..~+0.2- .~
. . 0Q.l
~
0 - r I IIII I
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Flowrate2 (kg/s)2
Figure 12. Performance of single pumps at three power settings, and
pumps in series at 10SW .
TECQUIPMENT H32 SERIES AND PARALLEL PUMP TFST SET- --
Considering that the powers were not measured, but are the manufacturer'spublished values, the correlation shown in Figure 13 is good. Taken together,the results confirm that the performance of pumps in isolation, and pumps inseries, is as expected.
The variation of pump efficiency with flowrate is shown in Figure 14, basedon the manufacturer's stated electrical power input.
0~
~Q)
'0~~
Flowrate (kg / s)
Figure 14. Variation of pump efficiency with flowrate.
TBCQUIPMBNT H32 SERIES AND PARALLEL PUMP TBSl' SET
The actual pump performance is shown plotted on the pump manufacturer'spublished curves for each of the three power settings in Figure 15. Over thenormal working part of the curve, the results agree extremely well, but tendto be higher at low flowrates.
60 + Single pump4OW
X Single pump70W
(f) Single pumpl05W
Selectric
1 X 240V 50Hz(! !)
(!) (!) (!)I
"""'"
50
40
.f
30...e~ /
20'"
#10
~0
0:2 O~.. 0:60 0.8 1.0 1.%
Litres/sec
Figure 15. Pump performance curves.
TECQUIPMBNT H32 SERms AND PARALLEL PUMP TEST SET
Pumps in parallel
Figure 16 shows the measured pressure against (flowrate)2 for pumps in
parallel at a power rating of 10SW. Similar results (not shown) were obtainedat a power setting of 4OW. It will be observed that the experimental resultsare higher than simple theory predicts, especially at high flowrates.
0.6
0.5
0.4
;,Q 0.3Q.
Expecteddifference,= 0.09 bar
0.2
0.1
0
Kg/s2,Flowrate
Figure 16. Measured pressure against (flowrate)2.
The reason for the experimental results being higher than the predictedresults is that the pressure at exit from the p~rallel system is measured not inthe outlet pipe from the pump, but after the two flows have merged at theTee junction, as shown in Figure 17.
TBCQUIPMENT H32 SERIES AND PARALLEL PUMP TPSI SET
Figure 17. Schematic of pwnps in parallel (showing Tee junction).
The flowrates entering the junction are probably identical, but the flowleaving the junction has to be accelerated to twice the rate since the pipes areall the same diameter.
Consider the flow at the Tee junction as shown in Figure 18.
Figure 18. The Tee junction.
TBCQUIPMBNT H32 SERIES AND P ARALLBL PUMP TPST SET
The flow entering at 1 has to lose all momentum in its original direction. Thisincreases the static pressure in the junction, causing flow 2 to decelerate. Theactual flow is likely to be less than measured from the pumps in isolation. Anaccurate momentum and energy balance at the Tee junction is difficult, but itwould be expected that the local pressure rise would be of the order of 2dynamic heads. At the maximum flowrate of 1.6 kg/s, this is about 0.18 bar.The measured rise is 0.25 bar, which is equivalent to 2.8 dynamic heads. Theacceleration of flow 3 past the point where PI is measured could lead to a
reduction of pressure of 1 dynamic head (0.9 bar). These predictions line upwell with the measured results, as shown in Figure 19.
Figure 19. Pressure against flowrate for measured and ideal values.
Pwnp efficiencies
The efficiencies of pumps in isolation has already been shown. It isinstructive to collate the three possible pump configurations, and this isshown in Figure 20 for a power setting of 10SW. The trend is that single
pumps have the best efficiency I whilst the same pumps in parallel have
TBCQUIPMP.NT H32 SERIF.S AND PARALLEL PUMP TPST SET
maximum efficiencies some 5% less. Pumps in series tend to have efficienciesmidway between the single and parallel configurations.
11%
Figure 20. Efficiency against flowrate for three pump configurations.
General comments on the results
The apparatus demonstrates quite clearly the performance of pumps inisolation or in series. Because of the nahire of the pipework and the locationof the pressure tapping PI' the simple idealised parallel flow characteristics
are not altogether demonstrated. However, this is a valuable teaching point,real pumps are coIU\ected by pipes which influence the characteristic of thewhole system.
TBCQUlPMBNT H32 SERIES AND PARALLEL PUMP TFST SET
The parallel flow results would not have been closer to the ideal case even ifthe pressure tappings were located close to the pump outlets. This is shown
by the high reading of P2 measured in the pipe well before the Tee junction.
~QUIPMBNT H32 SBRIBS AND PARALLEL PUMP TEST SET
APPENDIX I
These values are included for those wishing to make a more accurateprediction of the pressure losses in the system, and the pump inlet pressures.
Loss coefficients for various fittings.
Pressure drop Ap = K ! P V22
V K= 0.5
K=O.4
VyK=1.8
K = 0.2 (gate valve open)
K=1.1
K=O.9
Single pump
1'"\
n
Total K = 1.1
TECQUIPMBNT H32 SBRIBS AND P ARALLBL PUMP TEST SET
