Determining HP of Pump for Lifting Water
Submitted by bmsingh on September 9, 2009 - 22:19
Kindly let me know the following;
How to calculate the HP of the water pump motor for lifting water from sump to Roof tank in residential buildings? Is there a general rule to be followed? Any standards or recommendations may kindly be provided.
B M Singh
bm.singh@hotmail.com
Comments
1. How to calculate the HP of the water pump
Dear Sh BM Singh.
Bookish answer to your question is available on 100's websites on this internet. You might have searched various sites to quench your thirst to satisfy you fully. You might have found that there are only two variables required to calcuate the water pump HP. 1) height of total lift of water 2) required flow Please take total height in meters and flow required in liter per minute. now multiply height(in meters) and flow (in liters per minute) now divide this by 4500 you will get theoretical HP of the pump.
Now there is a secret to calculate actual HP of the pump In my practical experience i did not find pump efficiency more than 30 %. In most cases it is less than 30 %. So to calculate actual HP you should multiply theoretical HP by 4. Actual HP is 4 times more than theoretical HP.
Second secret, Please calculate total suction lift from pump to sump bottom. please ensure water pump is capable of producing so much suction.
Third secret, please add 20 % to your actual height of water lift. These are called frictional losses.
Fourth secret, submersible pumps are more efficient than monoblock pump.
I think above points are useful to satisfy your question
Regards
AK Singla
Power Utilities Engineer, Panipat Refinery Panipat
AK SINGLA
PARADIP REFINERY TOWNSHIP
PARADIP
ORISSA
2. Determining HP of Pump for Lifting Water
The following link provides you a simple calculator to workout the HP of a pump.
http://www.gemi.org/waterplanner/excel/GEMI-Equations-Tool.xls
This inolves understanding of the pumping head, size of pipe, water requirement, friction losses, etc.,
The better way to calculate the HP is to consult a pump vendor and use the pump rating chart of a pump your planning to use.
3. Dear B. M. Singh, One first
Dear B. M. Singh, One first needs to determine the total head of water required i.e the length of the piping from the foot valve inside the sump to the pump suction flange and then add the height of the piping from the pump discharge flange to O/H tank. This is the total discharge head required. The horse power or Kw required is calculated as follows:Kw =flow in m3./hr X total head in metresX density of water / 3.6X102,000 X pump efficiency (in decimals).It would be simpler for you to contact the sellers of pumps to come take a look at the layout of his sump, O/H tank, etc. take measurements and then quote for a suitable pump. The seller has to know how to determine the power required from the drive motor. Regards S.S.RanganathanAdvisor Ion ExchangeBangalore
4. Dear B. M. Singh, For
Dear B. M. Singh, For calculating the horse power of the pump for lifting the water to roof top, it will be required to do the following:
With regards, Vijay Kumar Hydrologist Head-Water Resources/Senior Consultant-Water ResourcesDHI-Water and EnvironmentNew Delhi-110019
5. How to calculate the HP of the water pump
Dear Sir,
The horse-power (H.P.) of a pump can be determined by calculating the work done by a pump in raising the water upto H height in meters
Let the pump raise ‘W’ kg of water to height ‘H’ m
Then work done by pump = W X H Kg m = WQH mkg/sec
Where W → density of water in kg/m3. Is equal to app. 1.0
Q → water discharge by pump in m3/sec
The water horse power, Pw = (W × Q × H) /75 and the break horse power = ((W × Q × H) /75 X Efficiency }
Power or energy required per second to the pump water is Pw = QH kw and this determines the horsepower
Horse power of the pump is Pw x 1.341 HP
The above is the general formula. But for the design of your system, you should know the following in addition, the lift and the total head. The total head involve, friction loss while the water flow through the pipe, bed loss, loss at valve, junction, at various changes of diameter of pipe etc. Hence to design a system if you know the all values, then you can design the pump and motor horse power, (Discharge rate, Lift, total head)
The total head involve various frictional loss computations at different stage. These are useful to understand the system and design as a whole.
But in practical cases, due to exhaustive trial and error statistics, either recorded or practically performed and assessed, given the discharge, pipe diameter, and total height from sump to tank, an experience mechanic can tell the required horse power of the pump/ motor and pipe diameter.
PVC pipes and HDP hoses have low frictional loss than the metal pipes. Depending up on your overhead tank size, available volume of water, you can chose the pipe diameter and horse power by varying the time of pumping. If you want lesser time, choose higher horse power which is within the available discharge
For a 5 member family, 500 liter capacity tank, filling twice a day will suffice the need. Assuming the tank is at a height of say about 25 feet you may fit 1.5 h.p centrifugal self priming pump to lift water from 5 feet depth sump for a pipe diameter of one quarter inches. This might fill your tank of 500 liters in maximum of about 10 to 12 minutes. However this depends on the quality and make of the impeller and motor. An ISI standard pump might do.
This is for your enlightenment.
A. RAJA MOHAMED
GEOPHYSICIST, COASTAL ENERGY Pvt Ltd
bismi1234786@gmail.com
A. RAJAMOHAMED AMBALAM GEOPHYSICIST COASTAL ENERGY Pvt Ltd, CHENNAI +919443619352
6. Suitable pump/motor for 10 feet depth sump 20 feet lifting
Dear Mr Raja Mohammed
Please suggest the best pump with product make for my sump. Specifications are as follows:
Height: 7 feet; Length: 6.5 feet; Width: 6.5 Feet
Thanks,
Mohideen, Group Five - Saudi Arabia
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