Emergency Water with Pressure Tank on city water

[RooferTryingAllTrades]

I have installed a pressure tank into my home water system so that I don't have to refill the plastic water storage bricks every six months or pour my water out of this bricks when I need it. The issue I am having is that I have tried to explain to my wife that the water in the tank will rotate naturally. I can't convince her. Can someone help me have some confidence?

To simplify things, I just put a t after the water heater shut off, installed a gate valve and ran a line to the 120 gal tank. (30 days for 4 people. Have never needed 30 days worth of water or known anyone who has) As you all know these tanks don't function like a water heater, where there is a separate in and out. There is only 1 in/out. My thought about the water rotating is this. When water is used in the home, the pressure in the system drops, which means that the pressure in the tank will drop to equalize and water will flow out. Then when the water is turned off, the pressure from the city supply will bring the system back up to pressure and the tank will fill back up. Bam! Water rotated. (I'm not confident a significant amount of water will move. Will any water move?)

Is this sound thinking or do I need some valves or pumps or something else? Thanks in advance. Not in a hurry because I have six months before emergency supply needs to be rotated correctly.

 

[Fitter30]

Since your writing about a bladder type of expansion tank and city water pressure is much of a constant how is the water going to come out. Its not like a water heater that someone taking bath needs 60 gallons of hot water filling water heater with 60 gallons cold and have a little expansion. A potable water tank would be costly and would want a backflow devise to keep your water in your house not flowing back to the street.

 

[Sponsor]

 

[LLigetfa]

A captive air tank on a well system will exchange the water only because there is a repeated cycle of pressure going up 20 PSI and then down 20 PSI. You are never going to have that sort of cycling on city water.

Also, a 120 gallon tank with a pressure range between 60/80 holds only 25 gallons. If you want to have 120 gallons of water in reserve, get a contact tank and pipe it backwards so the inlet in at the top and the outlet is at the bottom. Then when the city water supply is down, turn off the supply and use an air compressor to inject air at the inlet. Later, when the water comes back on, purge out the air.

 

[Reach4]

I have installed a pressure tank into my home water system so that I don't have to refill the plastic water storage bricks every six months or pour my water out of this bricks when I need it. The issue I am having is that I have tried to explain to my wife that the water in the tank will rotate naturally. I can't convince her.

Nor can you convince me.

 

[Valveman]

As has been said with a steady pressure from the city the 25 gallons of water in a 120 gallon size tank will never be changed out until the city stops supplying water. When the city water pressure gets low the tank will push water into the house that has been sitting in that tank for a long time.

 

[RooferTryingAllTrades]

A captive air tank on a well system will exchange the water only because there is a repeated cycle of pressure going up 20 PSI and then down 20 PSI. You are never going to have that sort of cycling on city water.

Also, a 120 gallon tank with a pressure range between 60/80 holds only 25 gallons. If you want to have 120 gallons of water in reserve, get a contact tank and pipe it backwards so the inlet in at the top and the outlet is at the bottom. Then when the city water supply is down, turn off the supply and use an air compressor to inject air at the inlet. Later, when the water comes back on, purge out the air.

This sounds like drawdown when you are talking about 20 gallons from 80-60 psi. I hope if there is 80 psi in my max 100psi / 120 gal tank it should be 70-80% full. It started with 28 psi. Since I don't have a pressure switch, it's my thought I should be able to draw it down to empty if ever needed. The question comes with a desire to know how much water is in the tank based on psi. Is there some formula someone knows to output volume based on starting and max psi, size of the tank, and current psi?

 

[RooferTryingAllTrades]

In response to everyone thank you. (Except for the guy who agreed with my wife. I wouldve sided with you unless you were wrong I already bought the tank. I guess I could return it and get something more suitable, but I think for another 50 smackeroos, I can get a motorized ball valve and a check valve(which I'm pretty sure I need in case city water pressure goes down. Can't find any clear indication that the city has installed a check valve. Anybody have experience that can reasonably lead me to believe otherwise.) The gate valve after the city shutoff is horrible and needs to be replaced. I have to stick my arm down a pipe in the ground and try to put enough torque on the gate valve to actually close it fully. I sit at a desk all day so I'm never strong enough and getting a tool down there is not feasible. Anyhow I digress. If I get this motorized ball valve and the check valve and get the two in place where that gate valve is, every week or so I can turn the motorized ball valve off thus isolating the home system from the street system and creating a replica of what would happen if the pressure turned off from the street. Also, the motorized valve is a power off auto close valve which would automatically close if the power goes out preventing the very extremely unlikely backwards contamination from the city. Turning that off would cause the tank to draw down. Then when the city pressure is turned back on the tank would fill back up, thus cycling the water. Does this sound reasonable?

 

[Jadnashua]

What some people do is use a tank with a float valve so the tank is filled by the supply, then shuts off when the tank is full. Out of the tank, you can put a pump and pressure tank. Make the storage tank as big as you want, and if large enough, should the city water be off for some reason, it could also provide some water for fire fighting. THat storage tank could be buried outside as long as it was below the frost line.

The lower the air pressure in your tank, the more you'll stretch the bladder from the much higher city water pressure. If that doesn't burst the bladder, it will decrease its lifespan. They're typically designed for about a 20# delta from high to low. Exceeding that pressure delta is asking for trouble.

 

[LLigetfa]

This sounds like drawdown when you are talking about 20 gallons from 80-60 psi. I hope if there is 80 psi in my max 100psi / 120 gal tank it should be 70-80% full. It started with 28 psi.

You did not mention what the city water pressure is so I had to make assumptions.
If you have only 28 PSI precharge and the city water pressure goes up to 80 PSI, the diaphragm will be overstretched. Those diaphragms are designed for a 20 PSI differential, not 52 PSI.

 

[RooferTryingAllTrades]

You did not mention what the city water pressure is so I had to make assumptions.
If you have only 28 PSI precharge and the city water pressure goes up to 80 PSI, the diaphragm will be overstretched. Those diaphragms are designed for a 20 PSI differential, not 52 PSI.

Okay. This is getting complicated.
So if I empty the tank and bring the base psi down to 5psi, then fill it again, is that going to fix my problem of high delta? Isnt that going to make it worse because then the delta will be 75 psi since the tank isnt going to stop filling until pressure equalizes with line pressure?
So I should fill the tank with 60 psi and then it will only change by the target 20 lbs, but capacity is reduced to the 25 gallons discussed previously. Is that what you are getting at?

It leaves the question in my mind that why does it say 119 gal, if it cant hold that much because the pressure required to hold that much is too high? It sounds like there is not a way to get it to 119 gal. Is there?

 

[Reach4]

It leaves the question in my mind that why does it say 119 gal, if it cant hold that much because the pressure required to hold that much is too high? It sounds like there is not a way to get it to 119 gal. Is there?

Simple answer is no. Complicated answer is also no.

The 119 includes the air and the water both. If you want a number closer to what you want, look to look to the "drawdown" spec.

 

[Storm rider]

A well pressure tank is not the correct type of tank for what you seem to want to accomplish. You want a water storage tank.

 

[RooferTryingAllTrades]

Well I know what I want and its not an unpressurized water storage tank.

Is my best bet with my current situation to fill it to 60 pounds and then fill it up? Ill deal with the lower capacity.

If I need to have more capacity I will use an unpressurized tank system.

 

[Jadnashua]

If your water pressure is normally 80psi, then yes, precharge the tank to 60psi, and accept what you get in available water volume.

 

[LLigetfa]

I don't recall you mention the brand/model of tank. Some tanks have an internal diaphragm limiting dome that is supposed to keep the diaphragm from over-stretching.

 

[Reach4]

Ditttohead has pointed out that the big tanks designed for RO water can have a much larger drawdown for a given size. What they give up is that the last bit will be coming out at a low pressure.

 

[RooferTryingAllTrades]

https://www.lowes.com/pd/A-O-Smith-119-5-Gallon-Vertical-Pressure-Tank/1000565669

Now that I re-examine the user manual, its not branded. Pretty sure its someone else's tank with a sticker from ao smith.

Im going to call the customer service line to see if there is an internal diaphragm limiting dome. There are only 2 weld lines on the tank so I will assume based on comparison to the diagram above that it is different.

 

[Valveman]

A 119 gallon tank working from 80 to 60 will deliver 25.13 gallons of water. You can play with different low/high pressure numbers here.
https://cyclestopvalves.com/pages/minimum-pump-run-time-calculator

Just click on CSV1 and put 0.5 in for the demand, and you can play with different cut in and cut out pressures. But as has been said, more than 20 PSI delta and you overstretch the bladder. Plus, if the city stays at 80 PSI all the time, your only advantage is the tank will drain itself when you cut off the city supply. Which you will still have to do, and I would do every couple months instead of 6 months, to keep the water in the tank from turning green.

25 or even 50 gallons is not going to supply 4 people but for a day or two, much less 30 days.

Real water storage is done this way. You just fill with city water instead of well water.

 

[RooferTryingAllTrades]

A 119 gallon tank working from 80 to 60 will deliver 25.13 gallons of water. You can play with different low/high pressure numbers here.
https://cyclestopvalves.com/pages/minimum-pump-run-time-calculator

Just click on CSV1 and put 0.5 in for the demand, and you can play with different cut in and cut out pressures. But as has been said, more than 20 PSI delta and you overstretch the bladder. Plus, if the city stays at 80 PSI all the time, your only advantage is the tank will drain itself when you cut off the city supply. Which you will still have to do, and I would do every couple months instead of 6 months, to keep the water in the tank from turning green.

25 or even 50 gallons is not going to supply 4 people but for a day or two, much less 30 days.

Real water storage is done this way. You just fill with city water instead of well water.
View attachment 60261

Thank you valveman.