Flow rate on water well?

[Clarence Martin]

How is flow rate of a water well calculated ?

Well is 55 feet deep. 6 inch casing and water depth is at 35 feet. They drilled 20 feet past where they first found water. Had a new pressure tank installed and it is a 44 gallon Goulds pressure tank with 11 gallons that can be used up before the pump turns on to refill the tank. Takes exactly 1 minute to refill the pressure tank. Out of the garden hose , I can fill up 4 gallons or so. a minute..



Can someone tell me how many gallons per minute this well is actually producing ?


Thanks,

[David Weaver]

It sounds like 11.

[Jim Tabor]

Most pressure tanks on/off cycles are based on pressure, not gallons. Such as, pump comes on when the pressure drops below, say... 40psi and off when it reaches 45-50psi (adjustable). How do you know in was exactly 11 gallons? Could still be several gallons in the tank when it started pumping, if not, you would get air instead of water from the hose. (I think :rolleyes:)

[Mike Cutler]

How is flow rate of a water well calculated ?

Well is 55 feet deep. 6 inch casing and water depth is at 35 feet. They drilled 20 feet past where they first found water. Had a new pressure tank installed and it is a 44 gallon Goulds pressure tank with 11 gallons that can be used up before the pump turns on to refill the tank. Takes exactly 1 minute to refill the pressure tank. Out of the garden hose , I can fill up 4 gallons or so. a minute..



Can someone tell me how many gallons per minute this well is actually producing ?


Thanks,

Clarence

The tank is pressure dependent. It's not really taking 1 minute to refill 11 gallons, although that is what is happening. It's taking 1 minute to bring up the pressure to the Cut Out value, typically 55-60 psi, from a Cut In value of 30-35 psi. and stop the pump.
The only way to truly measure the output of the pump is to bypass the tank,and that will be head dependent and will vary with the amount of water, in inches, on top of your pump. inside the casing. If you know the make and model of the pump, the manufacturer probably has a pump curve for it that would show flow, vs pressure for given head values.
If you're getting 4 gpm out of the sillcock that's pretty darn good! Between your pump and that bucket are a lot of orifice restriction, elbows, filters, etc.

[Mike Chance in Iowa]

Do you have a copy of the well driller's log? That may give you a better idea of how much your well is producing. When I had my well drilled back in '95, the driller told me it was producing 30 gpm "off the truck pump" yet with the pump he installed down the well, it would produce 12 gpm. Because of the long distances involved, and the type of pressure tank installed, by the time the water made it to the house, if you turned on the kitchen faucet sink "full blast" it was about 1/3 of what a typical faucet would produce.

[Steve Jenkins]

Bypass the pressure tank and run the pump until the well goes dry then wait a given amount of time, say 10 minutes, turn the pump back on and measure the amount of water you can pump before it goes dry again. divide by the time you waited(10 minutes) and that will give you the gpm that the well is capable of producing. If you can't pump it dry that means that with that particular pump it produces more than the pump can remove.
I put in a well last year for lawn irrigation and it only produces 4 gpm so I installed a 2400 gallon storage tank. I just have to make sure that any zones that I run won't use more than 2400 gallons and the tank will refill overnight. the well pump has a sensor on it so it will shut off when it runs the well dry and a timer to turn it back on after 30 minutes giving the well time to refill. There is a second pump in the tank to pump to the irrigation system.

[Pat Barry]

If the best you can get is 4 gallons in a minute over an extended period, say a few minutes time like you would use for taking a shower,, then the capacity is 4 gals per minute. The size of the pressure tank has nothing to do with the flow rate, only the backup volume that is there so as to minimize the pump cycling.

[Larry Frank]

As mentioned in one of the posts, there is a lot between the well and the hose. You should also take a look at the size of the pipes and such. I have a well and it is good to understand your own well system. I always have an extra pressure switch on hand.

You probably would not want to be able to get the full output of the well to be available to the outside faucet as it would cause a pressure drop in your house.

I probably get around 4 gpm on an outside faucet at best. The only way to really increase that is to increase the size of the well pump, pressure tank and pipes. And that is only if you have enough water flow through the ground to supply the well tip.

[Von Bickley]

Everything is different depending on where you live. Around here, when they drill a well and get the casing in, they use a large air compressor to blow the well. They run a 1 inch pipe down the casing and use air pressure to blow the well. This does two things, it helps to clean out the casing and it lets the well driller know how much water is in the well. A good well man can look at the water coming out and know how much water you have. In most cases, a good pump will give you a little bit better GPM than the well man tags it.
In our area, the well man is required to put a metal tag on the casing that tells you the depth of the well, the water level, and the GPM. They will usually be very conservative on their estimate of the GPM. They do not want the tag to list the GPM higher than what the pump will actually put out.
Check your casing to see if you have a tag on it........

[Ole Anderson]

Two different issues here, first is how much your well produces, the second is how much your pump can pump. You may have a well capable of 100 gpm, but a pump capable of only 10 gpm. If your pump can pump a steady 10 gpm, your static well level (not pumping for some time) is 35 feet, and your water level is at 40 feet while pumping, and it is 50 feet to the top of your screen, then with a large enough pump your well has a capacity of 30 gpm. If your question was really what is the capacity of my pump, then several suggestions above will give you an idea. Personally I would ask the driller what model and hp pump did he install, (I presume a submersible pump?) then you can go online to the manufacturer's website and download a pump curve. That will tell you what the pump is capable of pumping at various total heads, which is the pressure at the pump, in feet of head (1 psi = 2.31 feet of head) plus the depth to the water. Then you need to figure out what the friction losses are in the pipe...ow, my head is starting to hurt. Most residential wells around here are 4" or 5" PVC pipe with a plastic or stainless steel screen and a submersible pump. A 6" well casing is usually a small commercial well size. I have gone up to 16" and 1500 gpm for lake augmentation and municipal wells. Usually 150 to 250 feet deep around here. Our health department generally won't let you go less than 100 feet deep unless you run through a good layer of clay first to make sure you aren't recycling your own septic water.

[David G Baker]

Don't have a clue about the math but my well combined with my pump is capable of putting out over 10 gallons a minute. The well is 121 feet deep and when I measured to see at what level the water was in the 5 inch pipe it was 10 feet from the top of the casing. The bigger the pump the larger the volume it can pump and the recovery rate is also a factor.

[Clarence Martin]

Don't know the answer to this, but I have 13 outlets for water: the outside faucets, sink in basement, washer in basement, 2 toilets, washer upstairs, 2 bathtubs, 2 bathroom sinks and 2 kitchen sinks. IF, I were to open ALL the faucets at once, would I still get 4 gallons per minute of water flow ?

[Jay Jolliffe]

My well is 420' deep & only produces 1.5 gal/min. Pump is 320' feet down & I have a static level 5' from the top of a 6'' casing. Sometimes it flows out the top.

[Mike Cutler]

Don't know the answer to this, but I have 13 outlets for water: the outside faucets, sink in basement, washer in basement, 2 toilets, washer upstairs, 2 bathtubs, 2 bathroom sinks and 2 kitchen sinks. IF, I were to open ALL the faucets at once, would I still get 4 gallons per minute of water flow ?

Probably not.
Flow is equal to the square root of the D/P across an orifice restriction, or system. You would be close to the nominal if you could ad them all together, but it's not exactly a linear equation.