Pressure Tanks in series

[Cam Seelye]

I have 2 - 86 Gallon pressure tanks to add volume to my system as my well pump is too small. The fix for the well pump is about $10,000, so I am opting for the additional pressure tanks first. Should I add the new tanks between my pump and current pressure tank or between my current pressure tank and the house? I am not sure which side of the pressure switch the tanks should be on.

My current pressure tank is only a 20 Gallon and there are 5 people using water in our home.

Thanks!

 

[Reach4]

Keep them close with a big pipe between, and they should be fine either way. I am not a pro.

 

[Sponsor]

 

[LLigetfa]

I don't see how adding big tanks solves a problem with a pump that is too small. After the tanks are drawn down, they will present a much bigger load on the pump as it tries to keep up with the water use and try to fill those big tanks at the same time.

 

[Reach4]

After the tanks are drawn down, they will present a much bigger load on the pump as it tries to keep up with the water use and try to fill those big tanks at the same time.

Suppose, we have a 40/60 pressure switch. Suppose the pump puts out 4 gpm. Suppose the tank capacity is exhausted, and let's neglect the reserve between the air pressure precharge and the cut-on for this part:

1. If the pressure tank is 20 gallons we get 4 gpm available for immediate continuous use.
2. If the pressure tank is 172 gallons we get 4 gpm available for immediate continuous use.

Now suppose a different non-standard scenario. We have one 86 gallon tank (tank A) with a 36 psi precharge in parallel with a multi-dome construction tank (tank B) with a precharge of 28. Now when the pump goes on we could still draw some water down to 36 psi from tank A and B both. Below that, we could draw water down to 28 psi supplementing the 4 gpm from the pump.

What would be the effect of the 28 psi precharge on tank B? I think the diaphragm stretch gets limited by the dome, so it does not contribute beyond a certain pressure. However tank A is contributing fully.

Alternate water treatment scenario: Suppose there is an iron filter that needs 10 gpm for 8 minutes every 2 days at 2 am to backwash properly, but we have the 172 gallon tank with a 38 psi air precharge. We put a Fleck 5810 XTR2 valve on the iron filter. That offers flexibility. Instead of a single 8 minute backwash, we program in three 4-minute backwashes with 5 minutes between backwashes. The of the first 2 backwashes will be dropped to 4 gpm, so the media is not properly expanded. That could happen any time during the first backwash. The following backwash(s) will have enough volume stored to give a minimum of 4+4=8 minutes of backwash.

Most softeners use less than 4 gpm for their backwash, so a softener would not be a problem anyway.

 

[Valveman]

I could have swore I replied to this? Anyway, pressure tanks are just additional load for an already low producing well. If you want to store some water and have as much as needed to use, then you need a storage/cistern tank with a booster pump. And then a small pressure tank is all you need.

 

[Reach4]

I could have swore I replied to this? Anyway, pressure tanks are just additional load for an already low producing well.

I did not read this as a low producing well, but a low-producing pump.

With that in mind, I don't see the "additional load" thing.

 

[Valveman]

With the normal air charge, pressure tanks are empty before the pump comes on. Then not only does the pump have to supply the water needed, but also has to refill the pressure tank(s). The pressure tank is an additional load that has to be refilled before the pump shuts off.

Even with a low air charge, a pressure tank can only supply a few gallons more than the 4 GPM the pump is producing. Plus, the pressure must drop below the on pressure for the tank to supply ANY water. Then the low air charge in the tank prevents it from providing the full draw down at the regular on/off pressure.

Unless you have a true storage tank, when the pressure tank(s) are empty, all you have is 4 GPM. 4 GPM is 5,760 gallons per day that you can use anyway you want, if you have a storage tank and booster pump.

 

[Reach4]

With the normal air charge, pressure tanks are empty before the pump comes on.

If that were the case, I think he precharge should be dropped a bit, as it is with jet pumps.

Then not only does the pump have to supply the water needed, but also has to refill the pressure tank(s). The pressure tank is an additional load that has to be refilled before the pump shuts off.

How would a longer pump run be a negative? The user is still getting 4 gpm at that point regardless of tank size. Reminder: I picked 4 gpm for an example. Cam may have a significantly different flow. 4 gpm would correspond with about a 75 minute minimum run time with his 20 gallon tank. 50 seconds would correspond with 6 gpm.

Unless you have a true storage tank, when the pressure tank(s) are empty, all you have is 4 GPM. 4 GPM is 5,760 gallons per day that you can use anyway you want, if you have a storage tank and booster pump.

Factoring an atmospheric storage tank in the basement, dealing with possible chlorination, and a second pump, the $10000 for a new pump and heavier wires could start looking attractive.

 

[Valveman]

Longer run time is a good thing as long as it is a low producing pump and not a low producing well, which is usually the case. You could certainly get by with a few extra gallons in the pressure tank. But I would not want to be counting the gallons I had left after the pump came on. And I would not like the pressure decreasing below the start pressure. Storage tank, booster pump and controls can be 1500 bucks or so.

 

[Cam Seelye]

Thank you all for your responses. You are correct "valveman", I do not have a low producing well, I have an undersized pump. I am going to add a storage tank and booster pump if this doesn't make a big difference.

"LLigetfa" - I was told by a local well business that what wears the pump out is the constant turning on and off. There is not an additional "load" that I am aware of as the pump is always pumping the same water from the same place and to the same place. I am not an expert though, so maybe I am not understanding part of this.

 

[Cam Seelye]

Reach 4 - I had my well tested and it came back at 15gpm.

 

[LLigetfa]

...I don't see the "additional load" thing.

With bigger tanks, one suffers with low pressure for longer as it takes longer for the pump to come on. Then if the pump produces more than the draw, on a small tank the pressure quickly climbs and plateaus on the GPM curve. With a bigger tank, the little bit of extra the pump can produce is slowly soaked up by the tank (the extra load) and the pressure cannot climb nearly as fast so one suffers through that low pressure for longer.

IMHO, if the intent is to reduce cycling, then the CSV is a far better alternative. You suffer with poor pressure for a very short time as you draw down the tank but then your pressure will quickly climb and stay relatively constant unless you draw more than the pump can produce.

 

[WorthFlorida]

I.... The fix for the well pump is about $10,000, so I am opting for the additional pressure tanks first. ....Thanks!

Is this a submergible pump or above ground jet pump? How was the $10k figured? I kinda of agree with everyone else that a second pressure tank won't help much and 20 gallon is small to begin with. I would first go with one larger pressure tank and see how it works out before adding a second one. The second one can always be added later.

 

[Cam Seelye]

WorthFlorida -

I acquired 2 brand new "Well-X-trol" pressure tanks for really cheap, so I already have them on hand.

The $10K has more to do with the labor, permits and getting a heavier gauge electrical line run from the box in my house out to the well house than the cost of a larger well pump. The concrete top on the well house is also failing and needs to be replaced. I didn't share all of that initially because it has less to do with my question, but you asked.

I can obviously mitigate that cost by doing the heavy lifting myself, but I am looking at this in stages rather than dropping the $10k to have it all done for me.

 

[Cam Seelye]

With bigger tanks, one suffers with low pressure for longer as it takes longer for the pump to come on. Then if the pump produces more than the draw, on a small tank the pressure quickly climbs and plateaus on the GPM curve. With a bigger tank, the little bit of extra the pump can produce is slowly soaked up by the tank (the extra load) and the pressure cannot climb nearly as fast so one suffers through that low pressure for longer.

IMHO, if the intent is to reduce cycling, then the CSV is a far better alternative. You suffer with poor pressure for a very short time as you draw down the tank but then your pressure will quickly climb and stay relatively constant unless you draw more than the pump can produce.

I am drawing draining down the 6 gallons in my current tank while doing dishes, running the bath for my youngest two and doing laundry a the same time. Most of what we function on is what the pump can produce. My question from your comment is why would I have less pressure if I add two more pressure tanks to my system? I get that it will take longer to "cycle" or fill the tanks, but won't my pressure remain the same as it is now when the single tank is emptied? Or am I reading your response wrong?

 

[WorthFlorida]

I am drawing draining down the 6 gallons in my current tank while doing dishes, running the bath for my youngest two and doing laundry a the same time. Most of what we function on is what the pump can produce. My question from your comment is why would I have less pressure if I add two more pressure tanks to my system? I get that it will take longer to "cycle" or fill the tanks, but won't my pressure remain the same as it is now when the single tank is emptied? Or am I reading your response wrong?

As stated by the valveman, Cary, With the normal air charge, pressure tanks are empty before the pump comes on. Then not only does the pump have to supply the water needed, but also has to refill the pressure tank(s). The pressure tank is an additional load that has to be refilled before the pump shuts off.

It's simple, it takes energy to do anything and to pump an additional pressure tank at the same time to provide water for the bath and you may notice the flow rate will decrease. Here is a article that might explain it. Pressure is the force to move water and it takes energy. https://www.hunker.com/12000142/water-flow-vs-pressure

Cam,
When you get the two pressure tanks set up please update this post on performance. I'm sure you realize is you're using a small car trying to get the performance of a pick up truck. I've been there, small kids, mortgage, doctor bills, etc., then you get an abscess tooth. Sometimes it feels that it'll never end.

 

[LLigetfa]

My question from your comment is why would I have less pressure if I add two more pressure tanks to my system? I get that it will take longer to "cycle" or fill the tanks, but won't my pressure remain the same as it is now when the single tank is emptied? Or am I reading your response wrong?

When you current tank gets emptied and the pump starts, if there is more capacity than you are using, the pressure will rise since it takes less water to partially fill the tank. The pump runs on a curve meaning you get more GPM at lower pressure and less GPM at higher pressure. The bigger tanks will need more gallons (and so more GPM) so it will be further off the curve.

 

[Valveman]

A 44 gallon size tank will hold 10 gallons of water using a 40/60 switch and 38 PSI air charge. With a 28 PSI air charge the tank will hold about 14 gallons of water. The first 10 gallons in the tank will be used up by the time the pump starts. Then when you are using more water than the pump can supply the pressure will drop about 2 PSI for every extra gallon you get out of the tank. And there is only 4 gallons left in the tank. So, if the pump is producing 4 GPM, you can use 5 GPM for 4 more minutes or 6 GPM for 2 minutes as the pressure drops from 49 down to 28 PSI and the tank is empty.

 

[charlesey]

Recently, I just exchanged our water tank and forever when we fit the water on in the household it has a helping of air in it and sputa a helping. I’ve tried modifying the air with the valve on highest of the tank but not anything appears to work. Also, I’ve observed there is barely any water in the tank itself external.

 

[Valveman]

Bladder or diaphragm tanks should not get air in them and do not need a air release or an air volume control valve. Old style hydro=pneumatic tanks need a good air volume control valve mounted half way up the tank. Post a pic if you don't know what you have.