I need to install an iron backwashing filter and I need to get the gpm flow from my well pump. The instructions I get from sales people is to fill a 5 gal. bucket from a faucet close to the pressure tank. However the faucet inside dem. is about 5/8" and I only get 6 gallons using their formula. All the piping going into and out of the pressure tank is 1"if a draw water from an outside faucet that has a 1" shut off I get a 5 gal. bucket filled in 7 seconds. The bypass valve to the filter will be 1" so which figure should I use for sizing a iron filter.
thanks in advance for any information.

At the faucet, you get the gpm of that faucet. However, the gpm you need to consider is your "normal" maximum which is the amount when multiple faucets are opened at the same time.

if you hired me to do the job, i would run full size piping so there would be no question that i undersized it to cut corners.
smaller MAY be adequate but why take a chance?

I think he is asking about the gpm so he knows WHICH unit to buy, not the piping size.

Thanks for the replies hj. & packy.
the filter reqires 10 gpm. for backwashing the media. so am I to understand if I continue the 1'pipe to the filter that should be adequate. another thing I don't understand i when using the outside faucet i get 5 gal. fill in 7 seconds, but I can't believe that submersible pump is pumping 40+ gpm. am i missing something here?



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Look at it this way.
5 gallons in 7 seconds or every .714 seconds you get 1 gallon. (5 divided by 7 = .714)
.714 seconds times 60 seconds nets (.714 x 60) = 42.84 GPM

Side bar - The larger the pipe the slower the water moves.
It may need smaller pipe sizes to get the 15 fps (Not fpm) needed for backwashing.
Just sayin



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You'll get more GPM from your hose bibb than the pump can provide, the excess is coming from the pressure tank.

Did your water draw include the draw down from the pressure tank or was it strictly from the pump outlet?

Steve (CA)
The draw was off the pressure tank, but the iron filter will also be off the pressure tank.The filter i'm considering is a 1.5 cu.ft.Mang-Ox and needs 12 gpm for backwash.
do you think I'll be OK.

Thanks for the info.

Of course.