Why Is Pump Gallons Per Minute Rating Important if You are Using a Pressure Tank?

[Biddle]

I am planning to replace a 12-year old 1.5 HP, 5 GPM submersible pump in my 680 ft. well. I have a 50-gallon pressure tank. Water pressure has always been terrible. Not enough water pressure to run a single lawn sprinkler. Cannot take a shower and run the dish washer at the same time. I'm guessing my pump was not properly sized by the well driller when installed 12 years ago. The well driller report says the well can deliver 20+ GPM. I read that one consideration in sizing a pump is required GPM based on the number of water fixtures in the house and number of bathrooms. I have 17 water fixtures = 17 GPM and 2.5 bathrooms. At first I thought "No wonder I have such low water pressure. The house has a 17 GPM requirement and my pump is only capable of delivering 5 GPM". But why does that matter if I'm using a pressure tank?

 

[Valveman]

The water does not come from the pressure tank, it comes from the pump. A 50 gallon pressure tank only holds about 12-14 gallons of water. So when the tank is full you can use that 12 gallons as fast as you want. But when the 12 gallons in the tank is gone, all you have left is the 5 GPM the pump can produce. You cannot run a 3 GPM shower and a 3 GPM dish washer with a 5 GPM pump and have any pressure to speak of. I don't think you need a 17 GPM pump, but 10 GPM will usually run everything in the house that would happen to be on at the same time.

 

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[Biddle]

Thank you for your reply. It is much appreciated. 680 ft. is a long way to pump water. The well report from the drilling company 12 years ago says the static water level is 112 ft. Can that change over time or should it still be accurate? I read that pump stages provide lift. How do I determine how many stages the pump should have to accommodate 680 ft. ? Another concern is that often the literature says "submersible pumps to 400 ft." Does that mean a submersible pump is not appropriate for my 680 ft. well?

 

[Valveman]

Thank you for your reply. It is much appreciated. 680 ft. is a long way to pump water. The well report from the drilling company 12 years ago says the static water level is 112 ft. Can that change over time or should it still be accurate? I read that pump stages provide lift. How do I determine how many stages the pump should have to accommodate 680 ft. ? Another concern is that often the literature says "submersible pumps to 400 ft." Does that mean a submersible pump is not appropriate for my 680 ft. well?

I don't know why your pump is set at 680' if you have a static level of 112'? Your 1.5HP, 5 GPM pump will only produce 3 GPM and no pressure from 680'. But it will produce 7+ GPM with a static of 112' and still produce 50 PSI. So I am thinking you are using more than 7 GPM in the house when running more than one fixture at a time, which will cause low pressure.

I would probably set about a 1HP, 10 GPM pump at about 300'. With a static of 112' this would give you about 300 gallons stored in the well to 300'. This 1HP pump would produce 12-14 GPM when the water level is high, and would still produce 6 GPM under pressure if the water level pulled down to 300'. This would give you double the volume you have now, and would keep the pressure up in the house.

If your well is not strong enough to do this I would consider getting a cistern type storage tank for the well pump to fill. Then an additional booster pump in the cistern would supply as much volume and pressure as you want for the house.

Either way a Pside-Kick kit with a 4.5 gallon size tank would be all you need for the 1HP sub or a booster in a cistern. Again a pressure tank does not store water. It is only designed to limit the number of on/off pump cycles per day. And when you have a Cycle Stop Valve as in the Pside-Kick kit to stop the cycling, a large pressure tank is not needed. Your water is stored in the well and/or a cistern tank.

 

[Texas Wellman]

Also don't forget to check the size of the pipe supplying your house from the well tank and the distance. It needs to be at least 3/4" (I use 1") and eliminate any un-necessary fittings and bottlenecks.

 

[Biddle]

Thank you for the advice. I didn't mean to infer that the pump was set at 680'. The well is 680' deep. I have no idea at what depth the pump was set. The well driller's report doesn't say. I'll call him and see if he still has a record of my well from 12 years ago.

 

[Craigpump]

Call your local health dept for the pump permit.

 

[Biddle]

I've never heard of a pump permit before. I hope that's the case here in Tolland , Ct. Great idea. Thank you.

 

[Craigpump]

We have them in Southbury, Woodbury, Oxford, Newtown, Danbury....

On newer homes a CO won't be issued until the proper permits are pulled and signed off.

 

[Biddle]

I don't know why your pump is set at 680' if you have a static level of 112'? Your 1.5HP, 5 GPM pump will only produce 3 GPM and no pressure from 680'. But it will produce 7+ GPM with a static of 112' and still produce 50 PSI. So I am thinking you are using more than 7 GPM in the house when running more than one fixture at a time, which will cause low pressure.

I would probably set about a 1HP, 10 GPM pump at about 300'. With a static of 112' this would give you about 300 gallons stored in the well to 300'. This 1HP pump would produce 12-14 GPM when the water level is high, and would still produce 6 GPM under pressure if the water level pulled down to 300'. This would give you double the volume you have now, and would keep the pressure up in the house.

If your well is not strong enough to do this I would consider getting a cistern type storage tank for the well pump to fill. Then an additional booster pump in the cistern would supply as much volume and pressure as you want for the house.

Either way a Pside-Kick kit with a 4.5 gallon size tank would be all you need for the 1HP sub or a booster in a cistern. Again a pressure tank does not store water. It is only designed to limit the number of on/off pump cycles per day. And when you have a Cycle Stop Valve as in the Pside-Kick kit to stop the cycling, a large pressure tank is not needed. Your water is stored in the well and/or a cistern tank.

The well report says the well will deliver 20+ GPM. Do you recommend a 10 GPM pump because that is typical for a 1 HP pump and you think a 1 HP is a good balance between performance and cost? What determines the depth to set a pump? How do you calculate the number of gallons stored in the well? I'm trying to learn the basics. Thanks for your help.

 

[Valveman]

If the static level is really 112', and if the well really makes 20 GPM, I doubt that you are pulling the level down very much from the 112' mark. Even if you are pulling the water level down to say 300', that pump will produce about 7 GPM. And if 7 GPM is not enough to run a shower and anything else at the same time, I would use a larger pump like the 10 GPM series. But if when pumping for long periods of time the water level pulls down to about 280', the 10 GPM, 1HP won't pump anymore than the 5 GPM, 1.5HP. A 10 GPM, 1.5HP would work with a water level down to about 420'.

Rule of thumb is 1.5 gallons of water stored for every foot below static. So if the static is 112', and you set the pump at 300'. you would have 282 gallons to use before the water gets down to the pump. Typical house without irrigation only uses about 300 gallons per day. If the static is lower than 112' or if you use a lot of water outside, the pump will probably need to be deeper, and then the pump needs to be larger because it is deeper.

 

[Craigpump]

You should have someone come in and verify your info, static, yield, pumping level, well depth, pump size etc.

 

[Biddle]

My pump finally died for good and forced the issue. The circuit breaker tripped and could not be reset. I called Staven Brothers, a well drilling company that has a good reputation in Tolland, CT. They pulled my old 1.5 HP, 5-GPM pump and put in a new 1.5 HP, 7-GPM pump, and raised the pressure on my pressure tank. To test the water pressure, which has always been really bad, Staven Bros suggested I connect a hose and sprinkler to the drain value on the pressure tank, thereby, bypassing my two in-line water softeners. The result was outstanding water pressure for outside sprinklers. Staven Bros said they are confident that poor water pressure inside the house is the result of partially plugged water softeners. I have two water softeners in line to deal with a terrible iron problem. Next up, is to check the water softener heads to see if they are indeed clogged as Staven's believe. Would be good if that proved to be true because it would at last fix the problem of low water pressure inside the house. Thanks Craigpump, Valveman, and Texas Well Man for your words of wisdom. You are a great bunch of folks.