5 GPM well; how do I backwash? What happens if I pump well dry?

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Beets

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My well is rated at 5 GPM. I need to treat for H2S, so I've been using centaur carbon which has one of the lowest back wash rates. I'm curious if folks ever use a media that needs higher back wash rates than what the well outputs? I'm wondering if that could be managed by putting in a larger pump, and putting in some sort of flow restrictor downstream of the backwashing filter? I'm thinking a 10 GPM backwash for 15 minutes isn't likely to deplete a well. But 10 GPM for a few hours would not be a good story.

Additionally, everyone seems terrified of pumping a well dry. Why?
 

Beets

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These are all hypothetical questions. I don't honestly have a reason to be pursuing a different filter media....but I'm sure this scenario comes up. Would definitely like to understand.
 

Reach4

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The well storage depends on well diameter and distance between the static water level and the pump. See center column of first page of https://www.geotechenv.com/Reference_Pages/water_measure_tables.pdf It says, for example, that a 4 inch well holds 0.653 gallons/ft, and a 5 inch well holds 1.020 gallons/ft.

I also use Centaur Carbon. I think some other media is better for higher levels of iron. My iron is less than 0.5 ppm.
 
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bingow

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Additionally, everyone seems terrified of pumping a well dry. Why?
I stupidly ran our 8 GPM (max) well "dry" by leaving a hose running unattended or over an hour, flushing out a gopher burrow. Actually, it started pumping so much sediment that it totally clogged the whole-house filter, which finally caused the pressure tank to shut down the pump. It took three days and several filter flushes for the water to return to normal. That occurred 10 years ago; the pump is now 22 years old. Specs: 240V ¾ HP Grundfos pump, positioned 140' deep in a 200' well, 4½" PVC casing,
, with original static water level at 22'.
 

Beets

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Thank you. Next question.....how do you limit the flow of your well? Is it as simple as pinching in a valve, or are there flow restrictors that can be purchased?
 

LLigetfa

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A dole valve is what should be used to limit GPM if that is really the end goal. A partially closed ball valve is hard to control precisely and will wear over time.

Limiting GPM negates the available storage in the well and prevents short term higher GPM for backwashing or other uses so IMHO it is Draconian.

A CSV is a variable GPM limiter that lets you use more GPM only when needed without pulling max GPM all the time. Combined with Cycle Sensor, it will prevent the well being pumped dry.
 

Reach4

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Thank you. Next question.....how do you limit the flow of your well? Is it as simple as pinching in a valve, or are there flow restrictors that can be purchased?
Limit the flow of my well? I don't do anything specifically. The current loads are such that that I don't suck the well dry. If I had a longer backwash or higher gpm backwash, my iron+H2S could suck my well down I expect.
 

MaxBlack

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Re: fear of pumping dry, afaik you can burn-out your deep well pump, despite that it no doubt has an overload cutout. A protection for such is Franklin's Pumptec-Plus, which protects against over and under load and voltage, low yield wells, mud/sand clogging, cavitation, drop in water level, rapid cycling, and faulty check valves. Last one I bought cost $285 back in 2006.
 
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