Hydraulics Lab - ECIV 3122 Experiment (12): Series & Parallel Pumps
Experiment 12: Series and Parallel Pumps
Introduction to the Equipment
The apparatus consists of a tank and pipework which delivers water to and from two identical centrifugal pumps. The unit is fitted with electronic sensors which measure the process variables. Signals from these sensors are sent to a computer via an interface device, and the unit is supplied with data logging software as standard.
The speed of one of the pumps may be varied to allow the collection of performance data over a range of parameters. Outlet pressures may be varied to control the flow rate. Flow through the system may be set to allow single pump operation, series pump operation or parallel pump operation.
Figure 1: Series and Parallel Pumps Demonstration Unit
Pumps
The two pumps are motor-driven centrifugal pumps. On pump 1 the speed of the motor is adjustable to give a range of 0 to 100%, allowing operation as a single pump for pump performance analysis. Pump 2 is an identical model but is run at its design speed, which is equivalent to a setting of 80% on the variable-speed pump for a 50Hz electrical supply, or 100% for a 60 Hz supply.
The pump bodies and cover plates are made from clear acrylic, allowing the impellers to be observed.
Inlet valve
A manual ball valve controls the inlet (suction) head supplied to the pumps. This valve should be fully open except when investigating the effect of inlet pressure on pump performance and cavitation formation.
Setting the flow path
The system may be configured to drive flow using single, series or parallel pumps. The system valves are as shown:
Valves should be set to configure the system as follows. The software should also be set to the corresponding flow path to ensure that the correct calculations are performed.
Single Pump:
Series Pumps:
Parallel Pumps:
Exercise F
Objective
To investigate the result on discharge and total head of operating pumps in series.
Theory
A single pump may be insufficient to produce the performance required. Combining two pumps increases the pumping capacity of the system. Two pumps may be connected in series, so that water passes first through one pump and then through the second. When two pumps operate in series, the flow rate is the same as for a single pump but the total head is increased. The combined pump head-capacity curve is found by adding the heads of the single pump curves at the same capacity.
Figure 2
Equipment Set Up
Ensure the drain valve is fully closed.
If necessary, fill the reservoir to within 10 cm of the top rim.
Check that both pumps are fitted with similar impellers (the impellers may be viewed through the clear cover plate of each pump).
Ensure the inlet valve and gate valve are both fully open.
Set the 3-way valve for flow in series (the earlier experiments have all used this valve set for flow in parallel).
Ensure the equipment is connected to the IFD7 and the IFD7 is connected to a suitable PC. The red and green indicator lights on the IFD7 should both be illuminated.
Ensure the IFD7 is connected to an appropriate mains supply, and switch on the supply. Switch on the IFD7.
Run the FM51-304 software. Check that 'IFD: OK' is displayed in the bottom right corner of the screen and that there are values displayed in all the sensor display boxes on the mimic diagram.
Procedure
Both pumps must be used at the same setting in this experiment, to ensure identical performance. As the speed of Pump 2 is fixed at its design operational point, Pump 1 should be set to match - select 80% for a 50Hz electrical supply, or 100% for 60 Hz.
Allow water to circulate until all air has been flushed from the system.
If results are already available for a single pump across its full flow range, load those results into the software now and jump to the section of this exercise using two pumps. If results are not available then proceed as follows:
Single pump performance:
Close Pump 2 outlet valve and open Pump 1 outlet valve.
In the software, on the mimic diagram, set the 'Mode' to 'Single' by selecting the appropriate radio button.
Rename the results sheet to 'Single'.
Select the icon to record the sensor readings and pump settings on the results table of the software.
Close the gate valve to reduce the flow by a small amount. Select the icon again.
Continue to close the gate valve to give incremental changes in flow rate, recording the sensor data each time.
After taking the final set of data, fully open the gate valve.
Series pump performance:
Create a new results sheet using the icon. Rename this new results sheet to 'Series'. In the software, on the mimic diagram, set the 'Mode' to 'Series' by selecting the appropriate radio button.
Open Pump 2 outlet valve, close Pump 1outlet valve and wait for any air to circulate out of the system.
Select the icon to record the sensor readings and pump settings on the results table of the software.
Close the gate valve to reduce the flow by a smallincrement. Select the icon again.
Continue to close the gate valve to give incremental changes in flow rate, recording the sensor data each time.
After taking the final set of data, fully open the gate valve again.
Exercise G may be performed immediately after this experiment without closing the software; otherwise, save the results and ensure they are available for Exercise G when required. (It may also be advisable to save the results from this exercise before starting exercise G even if continuing straight on, to ensure that the data is not lost in the event of a computer failure. The results sheet may be overwritten with the combined results once Exercise G has been completed).
Results
On a base of flow rate, plot a graph of total head gain for the single pump and for two pumps connected in series. Calculate the difference between the total head gain for single and series pumps.
Conclusion
Does the total head gain for the two pumps in series match the theoretical prediction of twice the head gain for a single pump (assuming the two pumps used gave identical performance)?
Give examples of applications where pumps might be connected in series
Figure 3 Figure 4
عند توصيل المضخات على التوالي فإن قيمة H تزداد.
و لرؤية ذلك عمليا، يجب أن تكون قيمة التدفق التي نقارن عندها منخفضة (أي أن outlet valve مفتوح قليلا) حتى يكون الفرق بين head لمضخة واحدة و لمضختين على التوالي واضح، كما بالشكل المجاور.
Figure 5
Low Flow High Flow
Exercise G
Objective
To investigate the result on discharge and total head of operating pumps in parallel.
Theory
A single pump may be insufficient to produce the performance required. Combining two pumps increases the pumping capacity of the system. Two pumps may be connected in parallel, so that half the flow passes through one of the pumps and the other half through the second pump. When two pumps operate in parallel the total head increase remains unchanged but the flow rate is increased. The head-capacity curve is found by adding the capacities of the single pump curves at the same head.
Figure 6
Equipment Set Up
Ensure the drain valve is fully closed.
If necessary, fill the reservoir to within 10 cm of the top rim.
Check that both pumps are fitted with similar impellers (the impellers may be viewed through the clear cover plate of each pump).
Ensure the inlet valve and gate valve are both full y open.
Set the 3-way valve for flow in parallel
Fully open the Pump 1 outlet valve and Pump 2 outlet valve. Opening both valves fully ensures that the outlet pressure on both pumps is equal.
Ensure the equipment is connected to the IFD7 and the IFD7 is connected to a suitable PC. The red and green indicator lights on the IFD7 should both be illuminated.
Ensure the IFD7 is connected to an appropriate mains supply, and switch on the supply. Switch on the IFD7.
Run the FM51-304 software. Check that 'IFD: OK' is displayed in the bottom right corner of the screen and that there are values displayed in all the sensor display boxes on the mimic diagram.
In the software, on the mimic diagram, set the 'Mode' to 'Parallel' by selecting the appropriate radio button
Procedure
Both pumps must be used at the same setting in this experiment, to ensure identical performance. As the speed of Pump 2 is fixed at its design operational point, Pump 1 should be set to match - select 80% for a 50Hz electrical supply, or 100% for 60 Hz.
Allow water to circulate until all air has been flushed from the system.
Exercise F should be performed before this experiment, and the results loaded into the software if the software is not still open from that exercise. If the software is still open from Exercise F then create a new results sheet by selecting the icon.
Rename the current (blank) results sheet to 'Parallel'.
Select the icon to record the sensor readings and pump settings on the results table of the software.
Close the gate valve to reduce the flow by a small increment. Select the icon again.
Continue to close the gate valve to give incremental changes in flow rate, recording the sensor data each time
After taking the final set of data, fully open the gate valve. Set Pump 1 to 0% and switch off both pumps
Results
On a base of flow rate, plot a graph of total head gain for the single pump and for two pumps connected in parallel. Calculate the difference between the capacity for single and parallel pumps.
Conclusion
Does the total head gain for the two pumps in parallel match the theoretical prediction of twice the capacity of a single pump (assuming the two pumps used gave identical performance)?
Compare the graphs for pumps in series and pumps in parallel, and describe the similarities and differences.
Give examples of applications where pumps might be connected in parallel. Drawing on the conclusions of earlier exercises, contrast these with applications where it would be more appropriate to connect pumps in series, and also with situations where it would be more appropriate to select a single pump of higher performance.
Hydraulics Lab - ECIV 3122 Experiment (12): Series & Parallel Pumps
ملاحظات:
-عند توصيل المضخات على التوازي فإن قيمة Q تزداد.
-و لرؤية ذلك عمليا، يجب أن تكون قيمة التدفق التي نقارن عندهاعالية (أي أن outlet valve fully opened) حتى يكون الفرق بين flow لمضخة واحدة و لمضختين على التوازي واضح، كما بالشكل المجاور.
Figure 7
Low Flow High Flow
-تكون فقاعات الهواء التي تسبب cavitation عند إغلاق inlet valve تدريجيا في تجربة 10 أوضح منه في تجربة 9.