Pressure Tank Sizing

[Nicholas Mackie]

Hello,

I am looking to install a shallow well jet pump system to my home. The pump I am considering using is a 1HP shallow well jet pump. I have 2 wells at roughly 20' with a selector valve to run off of one or the other. My question is, What size of a pressure tank would be suitable for this size pump and more so for keeping good pressure in my house at all times? I know there are many factors that play into size selection and practical application for the household. I am more worried about undersizing my tank than oversizing.

My house will have 4 sink faucets, 2 shower heads, an 80 gallon bathtub, tankless hot water heater, a clothes washer and a dish washer. Very rarely will any of them get used simultaneously other than sink faucets.

Any sort of recommendation would be much appreciated.

 

[Valveman]

The larger the pressure tank the longer your house will be at low pressure. The variation in pressure between 40 and 60 PSI as the pump cycles on and off will be seen throughout the house. At 40 PSI you will not have good shower pressure, at 60 you will have good pressure. Shower pressure is much stronger when the system is held at a constant 50 PSI than when cycling between 40 and 60. Plus you really need constant pressure to make an instant or tankless water heater work properly. Many times the pump cycling between 40 and 60 PSI will change the flow rate in the shower enough to cause an instant water heater to go and off, causing a cold water sandwich in the shower.

 

[Nicholas Mackie]

The larger the pressure tank the longer your house will be at low pressure. The variation in pressure between 40 and 60 PSI as the pump cycles on and off will be seen throughout the house. At 40 PSI you will not have good shower pressure, at 60 you will have good pressure. Shower pressure is much stronger when the system is held at a constant 50 PSI than when cycling between 40 and 60. Plus you really need constant pressure to make an instant or tankless water heater work properly. Many times the pump cycling between 40 and 60 PSI will change the flow rate in the shower enough to cause an instant water heater to go and off, causing a cold water sandwich in the shower.

Thank You Valveman, that was very insightful and helpful. I am pretty savvy when it comes to stuff like this and understand mechanics quickly but I am still unclear on a couple of things. If you have the time to answer (or even see this reply) it would help me out greatly.

I get the fact of the larger tank taking longer to fill and therefore producing lower pressure for a longer period of time. If I were to install one of these CSVs with my 1HP pump rather than the 2HP described in the video, would I still be able to achieve 50psi? Or is that only obtainable by having the larger pump? The pump I am looking at buying is 1HP with a flow rate of 7gpm at the depth of my well. From what I understood (or misunderstood) in the video, that doesn't sound like enough flow to produce constant 50psi.

Also, I am living remotely on a Bahamian island with constant power surges and outages which is why I was looking into a larger pressure tank (so I can still shower and use sinks when power is out for long periods of time. Not necessary, just convenient) Do you have any recommendation on tank size? The "cold water sandwich" isn't much of an issue here since its so warm all of the time. The hot water is used in spurts to wash off soap and then back to cold. I can see where it might be an issue with clothes washer and tub filling though so thank you for that tip.

 

[Diehard]

It will be interesting to hear what Valveman has to say about your question.

In the mean time, based on your scenario of power outages and stored water requirements, here is something for you to think about.
An additional water storage tank on the house side of the well pump system. Installed in-line such that the water from your well pump would feed through the storage tank through a check valve. That way when you lose you well pump system the added (bladder type) storage tank will typically maintain the 40 to 60 psi pressure that your well pump provides. You can look up what size tank would be required to provide X number of gallons at a particular minimum pressure when pre-charged to 40 to 60 PSI.
(Incorrect capacity values removed.)

 

[Valveman]

A 1HP jet pump like a Goulds J10S can supply up to 12 GPM at 50 PSI from 50' depth. As long as you are using less than 12 GPM this pump could supply 50 PSI constant. Pressure tanks are not good for supplying water during power outages because you have no way of making sure they are full. An 86 gallon pressure tank only holds about 25 gallons of water, and that is when it is full at 60 PSI. With a 40/60 pressure switch, if the pressure happened to be at 42 PSI when the power goes off you would only have 2 gallons of water in the pressure tank. If you knew when the power outage would happen and went out and made sure the pressure tank was full to 60 PSI, then you would have 25 gallons stored. But you never know when the power will go off and have no way of making sure the pressure tank has some water.

A cistern or storage tank is the best way to store water. If you can elevate it you will gain 1 PSI for every 2.31' during a power outage. An extra jet pump can serve as a booster with the PK1A kit when there is power. You could also use an RV type pump that runs on 12V battery for times when the power is off.

 

[Nicholas Mackie]

A 1HP jet pump like a Goulds J10S can supply up to 12 GPM at 50 PSI from 50' depth. As long as you are using less than 12 GPM this pump could supply 50 PSI constant. Pressure tanks are not good for supplying water during power outages because you have no way of making sure they are full. An 86 gallon pressure tank only holds about 25 gallons of water, and that is when it is full at 60 PSI. With a 40/60 pressure switch, if the pressure happened to be at 42 PSI when the power goes off you would only have 2 gallons of water in the pressure tank. If you knew when the power outage would happen and went out and made sure the pressure tank was full to 60 PSI, then you would have 25 gallons stored. But you never know when the power will go off and have no way of making sure the pressure tank has some water.

A cistern or storage tank is the best way to store water. If you can elevate it you will gain 1 PSI for every 2.31' during a power outage. An extra jet pump can serve as a booster with the PK1A kit when there is power. You could also use an RV type pump that runs on 12V battery for times when the power is off.
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Valveman,
Thank you again for some very useful information! You seem to know a lot about well systems and I was wondering if there was any way I could contact you directly instead of through this forum? I would like to pick your brain about a few more things if possible. If you do not want to disclose any of your contact information on here I can give you my email and let you contact me. Let me know if this is something you are willing to do. Otherwise, thank you for your help!

 

[Valveman]

I like to do what I can on the forum so others can benefit from the exchange. But I do more over the phone than on the computer, so as long as this forum doesn't mind I don't either. 806-885-4445 Cary