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Dear All,
What is the minimum flow in centrifugal pumps & how it is evaluated. Also what happens at minimum flow for parallel centrifugal pumps.
Any good reference material will serve my purpose
Thanks in advance
Kiran G Parihar
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Minimum Flow In Centrifugal Pumps
Started by Guest_Kiran G Parihar_*, Mar 07 2006 04:22 AM
11 replies to this topic
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#2
Guest_Guest_*
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Posted 09 March 2006 - 12:34 AM
In most cases you will find minimum flow through a pump is required to have a thermally stable operation. This is, what you could say, to dissipate the enenrgy (temperature) build-up within the pump. Note use of the term 'Minimum Continous Flow' in API 610 datasheets. It requires the same under two conditions, stable and thermal.
As to the part on pumps in parallel, please be more specific. Typically, I would not expect any impact on the minimum flow requirement of a pump, whether it is operating as a standalone pump or in parallel with other pumps, with good engineering practice (as opposed to economic considerations adopted at some locations)requiring each pump to have its own minimum flow control system.
Regards
As to the part on pumps in parallel, please be more specific. Typically, I would not expect any impact on the minimum flow requirement of a pump, whether it is operating as a standalone pump or in parallel with other pumps, with good engineering practice (as opposed to economic considerations adopted at some locations)requiring each pump to have its own minimum flow control system.
Regards
#3
Guest_Guest_*
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Posted 10 March 2006 - 06:37 AM
Some more info on the subject, gathered from another forum:
Minimum flow rate of centrifugal pumps is determined by the following criteria:
-temperature rise due to internal energy loss.
-internal recirculation in the impeller (with large impeller inlet diameter compared with outside diameter, the NPSH rises in the part-load range).
-increased vibration due to greater flow separation.
-increased pressure fluctuation at part load.
-increased axial thrust at low flow rates.
-increased radial thrust (especially with single-volute
pumps).
Regards
Minimum flow rate of centrifugal pumps is determined by the following criteria:
-temperature rise due to internal energy loss.
-internal recirculation in the impeller (with large impeller inlet diameter compared with outside diameter, the NPSH rises in the part-load range).
-increased vibration due to greater flow separation.
-increased pressure fluctuation at part load.
-increased axial thrust at low flow rates.
-increased radial thrust (especially with single-volute
pumps).
Regards
#4
Samuelth
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Posted 16 March 2006 - 11:39 PM
Hi, We had exactly the same problem of parallel operation of pump leading to plant shut down and complete destruction of Pump internals.
The parallel operation was required for higher load operation of the plant.
A detailed study was made for all pumps in parallel operation and minimum flow protection and solutions are being implemented. It is applicable for both parallel operation and single pump operation.
In our case, the parallel operation posed a condition (due to higher flow through the Discharge line CV) in the instrumentation logic when the discharge line and minimum flow line control valve were closed during an emergency shut down.
Method of calculation. (Condition- The discharge line is closed and minimum flow valve is closed or there is no minimum flow line while pump is running)
1. The minimum flow given by manufacturer is only a guide
2. The minimum flow by many other reference also need verification and changes for your specific application
3. The steps are:-
1) Calculate the volume inside the Casing
2) Calculate the thermal energy generated (by energy of rotating impeller converting mechanical energy to heat energy- less energy lost in vibration, heat dissipation to outside etc-)
3) Estimate thermal losses to outside
4) From Process parameters, Calculate the temp at which cavitation starts (Please note the most dangerous period is just after cavitation starts when the bubble formation and collapse are maximum. At higher temp, with more vapors, the damage is lesser)
4) Calculate the time taken for temperature rise within the casing to reach the cavitation temperature as above
5) If the time taken is in minutes, you need an alarm or automatic Shut down of the pump. This time is calculated by steady state temperature balanced by thermal losses and heat generation by impeller
6) Provide required instrumentation.
7) Please note that this is for extreme case of cavitation damage. (We had scrapped the pump due to complete deformation of metallic parts inside) The mechanical damage of mech seal, bearings, shaft etc can happen before this stage as mentioned in previous posting.
I can give more information to those who are interested. A paper is made for publication in one of the magazines
Samuel
The parallel operation was required for higher load operation of the plant.
A detailed study was made for all pumps in parallel operation and minimum flow protection and solutions are being implemented. It is applicable for both parallel operation and single pump operation.
In our case, the parallel operation posed a condition (due to higher flow through the Discharge line CV) in the instrumentation logic when the discharge line and minimum flow line control valve were closed during an emergency shut down.
Method of calculation. (Condition- The discharge line is closed and minimum flow valve is closed or there is no minimum flow line while pump is running)
1. The minimum flow given by manufacturer is only a guide
2. The minimum flow by many other reference also need verification and changes for your specific application
3. The steps are:-
1) Calculate the volume inside the Casing
2) Calculate the thermal energy generated (by energy of rotating impeller converting mechanical energy to heat energy- less energy lost in vibration, heat dissipation to outside etc-)
3) Estimate thermal losses to outside
4) From Process parameters, Calculate the temp at which cavitation starts (Please note the most dangerous period is just after cavitation starts when the bubble formation and collapse are maximum. At higher temp, with more vapors, the damage is lesser)
4) Calculate the time taken for temperature rise within the casing to reach the cavitation temperature as above
5) If the time taken is in minutes, you need an alarm or automatic Shut down of the pump. This time is calculated by steady state temperature balanced by thermal losses and heat generation by impeller
6) Provide required instrumentation.
7) Please note that this is for extreme case of cavitation damage. (We had scrapped the pump due to complete deformation of metallic parts inside) The mechanical damage of mech seal, bearings, shaft etc can happen before this stage as mentioned in previous posting.
I can give more information to those who are interested. A paper is made for publication in one of the magazines
Samuel
#5
suresh2
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Junior Member
Posted 17 March 2006 - 10:46 AM
Dear Samuel,
I am a chemical engineering graduate student. I am very much interested in Pumps and Valves topic.
I would appriciate if you could provide me with further infromation.
Regards.
I am a chemical engineering graduate student. I am very much interested in Pumps and Valves topic.
I would appriciate if you could provide me with further infromation.
Regards.
#6
Guest_Kiran G Parihar_*
Guest_Kiran G Parihar_*
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- guestGuests
Posted 20 March 2006 - 03:16 AM
Hi Samuel,
Thanks for your reply. Also would you mind sending me the article that refered. Definitly it would be quite helpful. My mail id is kirangparihar@rediffmail.com
Kiran G Parihar
Thanks for your reply. Also would you mind sending me the article that refered. Definitly it would be quite helpful. My mail id is kirangparihar@rediffmail.com
Kiran G Parihar
#7
anshulagr
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Brand New Member
Posted 27 March 2006 - 04:42 AM
Dear Samuelth,
please send me a copy of article at anshulagr@yahoo.com
Thanks
Anshul
please send me a copy of article at anshulagr@yahoo.com
Thanks
Anshul
QUOTE (Samuelth @ Mar 16 2006, 11:39 PM) <{POST_SNAPBACK}>
Hi, We had exactly the same problem of parallel operation of pump leading to plant shut down and complete destruction of Pump internals.
The parallel operation was required for higher load operation of the plant.
A detailed study was made for all pumps in parallel operation and minimum flow protection and solutions are being implemented. It is applicable for both parallel operation and single pump operation.
In our case, the parallel operation posed a condition (due to higher flow through the Discharge line CV) in the instrumentation logic when the discharge line and minimum flow line control valve were closed during an emergency shut down.
Method of calculation. (Condition- The discharge line is closed and minimum flow valve is closed or there is no minimum flow line while pump is running)
1. The minimum flow given by manufacturer is only a guide
2. The minimum flow by many other reference also need verification and changes for your specific application
3. The steps are:-
1) Calculate the volume inside the Casing
2) Calculate the thermal energy generated (by energy of rotating impeller converting mechanical energy to heat energy- less energy lost in vibration, heat dissipation to outside etc-)
3) Estimate thermal losses to outside
4) From Process parameters, Calculate the temp at which cavitation starts (Please note the most dangerous period is just after cavitation starts when the bubble formation and collapse are maximum. At higher temp, with more vapors, the damage is lesser)
4) Calculate the time taken for temperature rise within the casing to reach the cavitation temperature as above
5) If the time taken is in minutes, you need an alarm or automatic Shut down of the pump. This time is calculated by steady state temperature balanced by thermal losses and heat generation by impeller
6) Provide required instrumentation.
7) Please note that this is for extreme case of cavitation damage. (We had scrapped the pump due to complete deformation of metallic parts inside) The mechanical damage of mech seal, bearings, shaft etc can happen before this stage as mentioned in previous posting.
I can give more information to those who are interested. A paper is made for publication in one of the magazines
Samuel
The parallel operation was required for higher load operation of the plant.
A detailed study was made for all pumps in parallel operation and minimum flow protection and solutions are being implemented. It is applicable for both parallel operation and single pump operation.
In our case, the parallel operation posed a condition (due to higher flow through the Discharge line CV) in the instrumentation logic when the discharge line and minimum flow line control valve were closed during an emergency shut down.
Method of calculation. (Condition- The discharge line is closed and minimum flow valve is closed or there is no minimum flow line while pump is running)
1. The minimum flow given by manufacturer is only a guide
2. The minimum flow by many other reference also need verification and changes for your specific application
3. The steps are:-
1) Calculate the volume inside the Casing
2) Calculate the thermal energy generated (by energy of rotating impeller converting mechanical energy to heat energy- less energy lost in vibration, heat dissipation to outside etc-)
3) Estimate thermal losses to outside
4) From Process parameters, Calculate the temp at which cavitation starts (Please note the most dangerous period is just after cavitation starts when the bubble formation and collapse are maximum. At higher temp, with more vapors, the damage is lesser)
4) Calculate the time taken for temperature rise within the casing to reach the cavitation temperature as above
5) If the time taken is in minutes, you need an alarm or automatic Shut down of the pump. This time is calculated by steady state temperature balanced by thermal losses and heat generation by impeller
6) Provide required instrumentation.
7) Please note that this is for extreme case of cavitation damage. (We had scrapped the pump due to complete deformation of metallic parts inside) The mechanical damage of mech seal, bearings, shaft etc can happen before this stage as mentioned in previous posting.
I can give more information to those who are interested. A paper is made for publication in one of the magazines
Samuel
#8
Samuelth
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Brand New Member
Posted 27 March 2006 - 11:14 PM
QUOTE (anshulagr @ Mar 27 2006, 12:42 PM) <{POST_SNAPBACK}>
Dear Samuelth,
please send me a copy of article at anshulagr@yahoo.com
Thanks
Anshul
Hi, We had exactly the same problem of parallel operation of pump leading to plant shut down and complete destruction of Pump internals.
The parallel operation was required for higher load operation of the plant.
A detailed study was made for all pumps in parallel operation and minimum flow protection and solutions are being implemented. It is applicable for both parallel operation and single pump operation.
In our case, the parallel operation posed a condition (due to higher flow through the Discharge line CV) in the instrumentation logic when the discharge line and minimum flow line control valve were closed during an emergency shut down.
Method of calculation. (Condition- The discharge line is closed and minimum flow valve is closed or there is no minimum flow line while pump is running)
1. The minimum flow given by manufacturer is only a guide
2. The minimum flow by many other reference also need verification and changes for your specific application
3. The steps are:-
1) Calculate the volume inside the Casing
2) Calculate the thermal energy generated (by energy of rotating impeller converting mechanical energy to heat energy- less energy lost in vibration, heat dissipation to outside etc-)
3) Estimate thermal losses to outside
4) From Process parameters, Calculate the temp at which cavitation starts (Please note the most dangerous period is just after cavitation starts when the bubble formation and collapse are maximum. At higher temp, with more vapors, the damage is lesser)
4) Calculate the time taken for temperature rise within the casing to reach the cavitation temperature as above
5) If the time taken is in minutes, you need an alarm or automatic Shut down of the pump. This time is calculated by steady state temperature balanced by thermal losses and heat generation by impeller
6) Provide required instrumentation.
7) Please note that this is for extreme case of cavitation damage. (We had scrapped the pump due to complete deformation of metallic parts inside) The mechanical damage of mech seal, bearings, shaft etc can happen before this stage as mentioned in previous posting.
I can give more information to those who are interested. A paper is made for publication in one of the magazines
Samuel
please send me a copy of article at anshulagr@yahoo.com
Thanks
Anshul
QUOTE (Samuelth @ Mar 16 2006, 11:39 PM) <{POST_SNAPBACK}>
Hi, We had exactly the same problem of parallel operation of pump leading to plant shut down and complete destruction of Pump internals.
The parallel operation was required for higher load operation of the plant.
A detailed study was made for all pumps in parallel operation and minimum flow protection and solutions are being implemented. It is applicable for both parallel operation and single pump operation.
In our case, the parallel operation posed a condition (due to higher flow through the Discharge line CV) in the instrumentation logic when the discharge line and minimum flow line control valve were closed during an emergency shut down.
Method of calculation. (Condition- The discharge line is closed and minimum flow valve is closed or there is no minimum flow line while pump is running)
1. The minimum flow given by manufacturer is only a guide
2. The minimum flow by many other reference also need verification and changes for your specific application
3. The steps are:-
1) Calculate the volume inside the Casing
2) Calculate the thermal energy generated (by energy of rotating impeller converting mechanical energy to heat energy- less energy lost in vibration, heat dissipation to outside etc-)
3) Estimate thermal losses to outside
4) From Process parameters, Calculate the temp at which cavitation starts (Please note the most dangerous period is just after cavitation starts when the bubble formation and collapse are maximum. At higher temp, with more vapors, the damage is lesser)
4) Calculate the time taken for temperature rise within the casing to reach the cavitation temperature as above
5) If the time taken is in minutes, you need an alarm or automatic Shut down of the pump. This time is calculated by steady state temperature balanced by thermal losses and heat generation by impeller
6) Provide required instrumentation.
7) Please note that this is for extreme case of cavitation damage. (We had scrapped the pump due to complete deformation of metallic parts inside) The mechanical damage of mech seal, bearings, shaft etc can happen before this stage as mentioned in previous posting.
I can give more information to those who are interested. A paper is made for publication in one of the magazines
Samuel
#9
Samuelth
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Posted 27 March 2006 - 11:43 PM
Hi,
I am attaching a short report giving the details of calcualtions and basic principles used for the minimum flow requirement/paralleloperation and time to cavitation damage. Hope this will be useful. As mentioned, I found results of many general methods, pump manufacturer's min. flow values and selection charts mentioned are all different (please refer report for comparison) We have to calculate for critical applications ourselves.
Even this calcuations are approximate for estimating heat losses. We can experimentally verify it if required.
Your comments are welcome.
Note: Since it is an internal company report which I am glad to share with you for interest of mutual learning, please do not quote it in any publications without our consent.
REL_M_118_05_Min_FLow_Pumps_revd_for_Cheresource27_3_06.doc 313.5KB
491 downloads
I am attaching a short report giving the details of calcualtions and basic principles used for the minimum flow requirement/paralleloperation and time to cavitation damage. Hope this will be useful. As mentioned, I found results of many general methods, pump manufacturer's min. flow values and selection charts mentioned are all different (please refer report for comparison) We have to calculate for critical applications ourselves.
Even this calcuations are approximate for estimating heat losses. We can experimentally verify it if required.
Your comments are welcome.
Note: Since it is an internal company report which I am glad to share with you for interest of mutual learning, please do not quote it in any publications without our consent.
REL_M_118_05_Min_FLow_Pumps_revd_for_Cheresource27_3_06.doc 313.5KB
491 downloads
#10
Guest_Amri Zein_*
Guest_Amri Zein_*
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Posted 05 April 2006 - 12:47 AM
Hi Samuel,
I am interesting with your article about minim flow in centrifugal pumps. I want to learn more. Please send to me at: amri.zein@gmail.com
Thank's a lot.
Regards,
Amri
I am interesting with your article about minim flow in centrifugal pumps. I want to learn more. Please send to me at: amri.zein@gmail.com
Thank's a lot.
Regards,
Amri
#11
jetul
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Veteran Member
Posted 12 April 2006 - 05:31 AM
hi, semual....
thanks to u to providing the online link...
can u give me ur paper which can provide me the infor mation about pumps that could help me in interviews..
thanks in advance
jetul
regards
hi, samuel....
thanks to u to providing the online link...
can u give me ur paper which can provide me the infor mation about pumps that could help me in interviews..
thanks in advance
jetul
regards
thanks to u to providing the online link...
can u give me ur paper which can provide me the infor mation about pumps that could help me in interviews..
thanks in advance
jetul
regards
hi, samuel....
thanks to u to providing the online link...
can u give me ur paper which can provide me the infor mation about pumps that could help me in interviews..
thanks in advance
jetul
regards
#12
Guest_Guest_*
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Posted 12 April 2006 - 06:26 AM
There are good many free resources about pumps on the web. Have a look into these links
www.mcnallyinstitute.com
http://www.pumpworld.com/contents.htm
http://www.alfalaval...44&languageID=1
www.mcnallyinstitute.com
http://www.pumpworld.com/contents.htm
http://www.alfalaval...44&languageID=1
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