sizing of booster pump

[chan chan]

hi everyone,
i have a situation with booster pumps... please help me or advice.

i need to size a booster pump that will be place in a water utility main pipe line. i will be installing 3 booster pumps, one will be a spare.
here are the data.
GPM: 5MLD
TDH: 50 meters

what will be its hp rating to comply with those requirement?
please advice.
thanks.

 

[Artisi]

You need 3 booster pumps, with daily flow of 5MLD from 2 pumps --- yes?
You need to advise the flowrate at peak demand.
how was the head arrived, at maximum flow with 2 pumps operating or is it only static head?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

chan chan,

The name of these forums is eng-tips, not eng-answers.

So here's a tip - google or search on this site for "pump power equation". you can even download several apps if you like. You will need to know, or guess the efficiency of your pump - prob between 60-70%.

That's quite a low head for a reasonable flowrate so you might be looking at axial pumps instead of centrifugal units.

Hint - you're looking somewhere in the 40-50kW shaft rating for combined power so 20-25 per parallel pump.

Hint - use the same units - normally m3/hr or l/sec and kW or GPM, ft and hp


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chan chan]

I apologize sir...
thank you for for all the tips, its not that i didn't research about it i was only hoping for some answers to compare with mine if i'm on the right track.. its my first time handling pumps.
i really appreciate the responds.. thank you.

to mr.artisi,
i apologize for not responding sooner. i was just caught up with another task.
thanks to your respond.

 

[LittleInch]

The best way eng tips works is that you post what you have worked out and then ask if it is correct.

Just coming on and saying "please give me the answer" tends not to get many responses....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

chan chan : we are still non the wiser as to the operating conditions so can not offer any further info' than what has already been posted.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[SandCounter]

Chan Chan,

You can calculate water horsepower by multiplying flow times pressure and then dividing by some constant. Converting to and then using imperial units . . .

5 MegaLiters per day = 917.3 gpm
(

http://www.wolframalpha.com/input/?i=convert+5+megaliters+per+day+to+gpm

)

50 meters of head (of water) = 164.04 ft of head (of water) = 71.01 psi

gpm x psi / 1714 = HP

917.3 gpm x 71.01 psi / 1714 = 38 HP

This, however is water horsepower, to get the brake horsepower, you will have to divide by the efficiency of the pumps which, if centrifugal pumps, can be anywhere from 30% to 70%. If you do not have a standard group of pumps you use, go to a vendor/manufacturer and request a pump sized such that the best efficiency point matches your design point (50 meters @ 5MLD) and use that efficiency. For electrical horsepower, you will need to further divide by the efficiencies of the generators and motors in play.

When designing factors of safety into a pump system, you add to available horsepower rather then required head.

Hope this helps.

 

[Artisi]

SandCounter, that is ok of course if the pumps are running 24/7 and the flowrate is evenly spread over 24 hours, however that is very unlikely on a water utility pipeline that normally see much higher flowrate at peak times and very little flow off peak, hence my question to the OP re flowrate at peak demand.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[SandCounter]

Artisi,

Good point. Cycling the pump would require higher horsepower during run time to achieve the same daily flow.

Chan Chan,

Take your water horsepower (WHP) you would have calculated and multiply it by the square of one over the percent run time. So for example, 50% run time:

WHP x (1/50%)^2 = WHP for cyclical operation

38 HP x (1/50%)^2 = 152 HP

 

[LittleInch]

Also 5 million liters per day is not 183 gpm, thats the value for 1 Ml/day....it's 5 times that..... so water power is 5 times what you suggest.

As pointed out above this also assumes that your flow rate is as instantaneous one and not limited to say 8 hours per day.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SandCounter]

LittleInch,

Thanks for the catch. Got caught up in the unfamiliar unit and dropped the significant digit. I've updated the calc based on your comment.

 

[chan chan]

littleinch,
i will take your advise on how to use eng. tips. thanks.



sandcounter,

thanks for the tips, i will surely look on to that.
it will surely help me in this task.

 

[Artisi]

Chan Chan.
Your first requirement is to think out how this system will operate, power requirements will come later once an overall concept is decided upon.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)