Pump Power Required?

[watrax]

i have read an article of gould.com regarding pump selection. there were three criterias stated in that article 1.) Capacity Needed - How big must the pump be? 2.) Well Condition - Deep Well or Shallow Well? 3.) Discharge Condition - How much pressure is needed. Granting these 3 conditions are already known, i wanna know how to determine the required power (in Horspwer) in the selected pump? i notice that everytime i go to a store to purchase pump, they usually ask for the horsepower of the pump i want to purchase.

 

[Gary Slusser]

Pumps come in two parts, the wet end rated in gpm and the motor rated in hp. Once you know what peak demand gpm you need, then with a pump flow chart/pump curve chart, you find the horses needed to do the job.

 

[Sponsor]

 

[watrax]

where can i find this pump flow chart/pump curve chart in the internet? thanks

 

[Thatguy]

everytime i go to a store to purchase pump, they usually ask for the horsepower of the pump i want to purchase.

Then you ask them how efficient their pumps are at the GPM you want.

HP = GPMxHead/(40xEfficiency)

For 60% efficiency, 60 gpm, 100' head, you need
6000/2400 = 2.5 hp.

They want you to overestimate the size of your pump; it's a win-win; they make money and you never complain [because your system is way oversized].

And if you do complain, you're the one who spec'ed the pump hp.
Win-win.

If you pull out a calculator I think they will go from deaf, dumb and blind to pretty smart, pretty soon.

http://www.google.com/search?client...mp+curve"+efficiency+gpm+hp&ie=UTF-8&oe=UTF-8

 

[Waterwelldude]

To give some examples.

1hp 10gpm @ 100' with 50psi, and the same 1hp @ 200' may only give you
5gpm with 50psi.
The pump has to work harder to supply the same psi, in turn the gpm drops.

2hp 10gpm @ 100' will actually give a little more gpm say12 to 14gpm with
50psi, but set it at the 200' mark and it will give the 10gpm required, where the 1hp did not have enough power to supply the 10gpm at the deeper setting.

The depth to the water level will dictate the hp the is needed to supply a given amount of water at a required psi.


Travis

 

[Gary Slusser]

where can i find this pump flow chart/pump curve chart in the internet? thanks

AFAIK, all submersible pump manufacturers supply a curve for the various models and sizes of the pumps the make.

 

[watrax]

For HP=GPMxHead/(40%xEff.). i just want to clarify if the GPM indicated here is the desired water outflow(in GPM) at the faucets??

 

[Thatguy]

For HP=GPMxHead/(40%xEff.). i just want to clarify if the GPM indicated here is the desired water outflow(in GPM) at the faucets??

If the head is corrected for all the pipe and fitting losses leading up to a faucet, it should work.
For every PSI of pressure you want at the desired flow rate, add ~2.3' to the head. E.g., according to IRC 2000, a bathtub may require 4 GPM at 8 PSI.
I have links for computing friction pipe loss and some fitting losses if you need them.
Pump efficiency varies with GPM and pressure.

I'm waiting on my city water Co. to tell me the "pump curve" that I would see for my water supply as it goes into my house. The PSI is probably 30 to 80, maybe by ordinance.

You might want to get one of these
http://www.amazon.com/Toro-Flow-Pressure-Gauge-53351/dp/B000O5SP80

 

[Mr.Nice_Guy]

Pump sizing has absoultely NOTHING to do with HP.

Does this make sense.... "I need a car that will do 25 MPH - what HP do I need?"
It's like comparing a riding lawnmower to a moped. The mower is probably 12HP - can it do 25mph? Now what about a little motorized scooter or moped - much less HP, faster speed. [I don't even know what Hp those motors are - probably 3/4 ??]

Hopefully you see my point.

1. Determine max flow needed/wanted.
2. This will give you any friction head.
3. Determine elevation head.
4. Determine the 'pressure' head (i want x psi at this much elevation.

You now have your DUTY POINT. Look at pump curves to match that duty point. Then you will know how much HP that specific pump end needs.

I've found that this link is an excellent source for learning how to size a pump. Just download the 6th section:
http://www.us.grundfos.com/web/download.nsf/DownloadViewOne/8A92FF77621B7EC588256F7F006185B5?OpenDocument

The people who do this for a living don't really need to "Do the math" - they know what a certain HP can do (only after you give them A- the TDH or B- the flow)

 

[Gary Slusser]

Well the horses do count but only as the last and least important thing you need to know.

Pumps come in two parts, the wet end rated in gpm and the motor rated in hp. Once you know what peak demand gpm you need, then with a pump flow chart/pump curve chart, you find the horses needed to do the job.