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Pump selection/pumping station

Pump selection/pumping station

Pump selection/pumping station

(OP)
Hello... I'm doing project for the pump selection. I know pump max Q=525 l/s, and the elevation difference between reservoir and building is 34 meters. The Length of pipes before the pump is 20 m and after 60 m. There is a 90 degree bend before the pump and two 90 degree bends after.... and so on, I did the calculations for the total hf=126 m (for 0.2 m pipe diameter) and Hp=241.03 m Then for 0.3 m my hf=17.54m and Hp=69.45m. I know the Motor power range (60, 95, 180, 250 hp). And the efficiency of motor is 85%. I have few questions how can I calculate the Power output for pump so to find efficiency? I do have characteristic curves of different pumps how do I choose the right rpm? And how will motor power effect my calculations besides rpm? I also can do assumptions. Thank you a lot for the answer because I cant get the right efficiency ...  

RE: Pump selection/pumping station

A more reasonable velocity (probably around 3 m/s max) is obtained using a diameter of 0.5 m.  You're power cost will probably be very very high with those small diameters and a more economical design/operation life cycle will be obtained if you use a larger diameter to lower the pump(s) power costs.

"I know the Motor power range (60, 95, 180, 250 hp)."  A possible range of 60 to 250 hp means that you know nothing right now.  How do you know the power, if you can't even find the pump efficiency.  Correction: you have a range of pumps that you think are available to you.  Maybe you can buy enough of them to make something work here, if those pumps are suitable for your project after all.

Assume a pump efficiency of 0.75 for now and verify, and recalculate if necessary, after you select the actual pump(s).

Pumps don't output power, they use it.

Pump power required is flowrate * density * head / efficiencies.

Choose the pump that has the lowest operational life cycle cost, including its power consumption.

And how will motor power effect my calculations besides rpm?
The more power you need, the more it will cost to run it.

Higher rpm pumps normally are considered to require more maintenance and repairs.

Quote:

I also can do assumptions.
Really?  You can't get the efficiency, because you have to assume a value for efficiency now and verify it later.

How many pumps will you use?

Please consider finding someone to help you that knows what they are doing ... before anything really gets screwed up here.  You'll be paying for that wrong design for the next 25 years or more.

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

RE: Pump selection/pumping station

(OP)
Thank you.

RE: Pump selection/pumping station

999  Now my answer looks to me like I got up on the wrong side of bed this morning.  Any other questions, try not to be afraid to ask. Sorry I was such a grump.

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

RE: Pump selection/pumping station

I agree with Biginch....your piping seems too small, and you will pay for an excessive pressure drop with high electric bills.

The red flag is usually your calulated discharge velocity.

A reasonble "sweet spot" for liquid velocity in a properly designed pumping system is about 6 to 11 feet/second (but this can vary depending on the specifics of the liquid)

A second red flag telling you of a poorly sized system, IMHO is the ratio of your "gravity head" to the "total pump head" in your case, 34/126 or 0.27

I have found that the ratio, most commonly, will be between 0.75 and 1.25......

My opinion only

-MJC

   

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