SQFlex pump sizing; ok to run less head than rated for?

[Evan Byrne]

Hi all,

I made a last minute decision to go with a SQFlex pump over my SQ that I just received because I'd like my system to run PV direct. I have a CSV so I'd like to choose one of the centrifugal SQF's so I can use the cycle stop valve.

My well is 200ft deep with a 27ft static level. My question is; Is it ok to run a pump well under the minimum head on the curve chart? The pump that looks best for my application is the 16 SQF-10, however the head-range on the chart is 100ft-230ft. Is it ok to run a pump at ~30ft that is rated for 100-230?


Thanks for any input. Cheers.

 

[Valveman]

Your water maybe at 30', but the 40/60 PSI pressure you need up top will add 115' to 138' to the 30' lift, so you are OK.

 

[Sponsor]

 

[Evan Byrne]

Oh that's very interesting. Maybe I have been making a mistake when looking at pump curve charts. Should I be taking into account the pressure required at the top and adding that to the total head when reverencing a pump curve chart?

 

[Boycedrilling]

Yes, if your looking at a pump curve chart. It's showing the gallons per minute the pump will produce at varying amount of total dynamic head. Total dynamic head (TDH) has three components. First is pumping level below ground surface. This is very seldom the same as static water level. You are saying you have a static water level of 27 feet. Your pumping level could be anywhere from the 27 foot static level to full drawdown at 200 feet. So that number is somewhere between 27 and 200 feet. Next is friction loss from the pipe and fittings at your desired flow rate. This is dependant on flow rate, Pipe size and length and number of fittings. This could be anywhere from 5 to 25 feet of head. And last we have desired pressure at our desired flow rate on top of the ground. Multiply your desired pressure by 2.31 to calculate the feet of head required to obtain this pressure. For example, say you want 60 psi. That would be 138.6 feet of head. Add all three of these together and you have your TDH. So your TDH required could be anywhere from 170 feet to 363 feet. But will probably be between 200 and 300 feet.

some pump manufacturers publish charts that make it a little simpler. They show gpm at various discharge pressures at various pumping water levels.

 

[Evan Byrne]

Awesome thanks for the explanation!