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In my place, the city water system provides the water at pressure of between 2BAR - 4BAR. We live on the 3rd floor, with water boiler on the roof (5th floor) so the hot water are going up to the roof and coming back down, many times without a good pressure for a good shower..

The obvious idea is to add an electric water pump on the line to add pressure whenever someone is opening the tap. For some reasons, I want more sophisticated idea, that I think will be more reliable and helpful.

My idea was to add a pressure tank (like expansion vessel) with a bladder or diaphragm on the line (before the water boiler tank). To its "air side" (bladder or diaphragm) to connect air compressor with a dynamic proportional pressure regulator.

At some times on a day - the pressure regulator will let the air pressure in the bladder/diaphragm will let the air pressure drop down to 2BAR, so the water will come in from the city system (using the 'native' pressure, without a pump help). Other times, the air pressure will be raised to about 6BAR, pressing the water towards the home, and if the tank has - let's say - about 200 litre, it will have very long time until the next need to re-fill it.

I thought about 200-300 litre pressure tank (will be held at about 6BAR), with air compressor with 50-100 litre air tank (at about 8-10 BAR).

AFAIK - Such a bladder water tank of 200 litre will cost here about 250$, and air compressor will cost about 150$-200$. I'll also need the proportional pressure regulator and the plumbing, but generally that's it.

Am I right?

Any insights would be welcomed.

FreeMan
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Offer
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  • Is this work which you are permitted to perform? Sounds like an apartment. What would your landlord say? – MonkeyZeus Feb 17 '21 at 19:44
  • How is water going to get into the tank charged at 6 bar when the normal water pressure is 2-4 bar? A booster pump fed from a cistern would be the normal route with the cistern sized for the maximum flow difference. Sure what you ask with an over complicated, air over water could work but a much larger tank would be needed and it would need to be pressure rated where a cistern just holds water and then you pump it at the pressure you desire. – Ed Beal Feb 17 '21 at 19:54
  • @EdBeal As I said: "On some times on a day - the pressure regulator will let the air pressure in the bladder/diaphragm will let the air pressure drop down to 2BAR, so the water will come in from the city system (using the 'native' pressure, without a pump help)." – Offer Feb 17 '21 at 20:01
  • If I understand your setup, the hot water only comes down, cold water goes up to replace it. – crip659 Feb 17 '21 at 21:33
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    Offer, I understand but your “pressure tank” having to be vented or valved off and around would be horribly inefficient, refilling without venting a costly method. Will you be able to afford a pressure tank large enough? Your ma. Pressure 8-10 bar these tanks require certification at my location fof much lower pressures 10 x 14.7 or 147 psi roughly. A small booster pump in a tank non pressure rated will be orders of magnitude cheaper to build and run. – Ed Beal Feb 17 '21 at 21:47
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    Where are you on this planet? – ThreePhaseEel Feb 18 '21 at 00:20
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    pumping water into a pressure tank is easier than pumping air. this is why off-the-shelf domestic supply pumps work that way. – Jasen Feb 18 '21 at 00:34
  • @ThreePhaseEel Thanks for asking. I'm from Jerusalem, Israel. For some (not technical) reasons, I have to 'buffer' enough water that will flow into home without turning on the electricity (pump). So I wanted to make this setup (electricity needed only to pressure the air, water are entering the expansion tank 'by themselves', and if there is enough pressure in the tank - water will be available to home without electricity also). – Offer Feb 18 '21 at 04:56
  • @EdBeal Thanks for looking into this. I've edited my question and added the cost estimation for this setup as I see it. What do you think? – Offer Feb 18 '21 at 05:01
  • Cost estimates are inappropriate as they vary around the world and will be wrong due to changing prices within weeks. – FreeMan Feb 18 '21 at 11:53
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    Overcomplicating is **not** more sohpisticated, **nor** more reliable. – Ecnerwal Feb 18 '21 at 13:51
  • Dear @FreeMan, thanks for your comment and for improving the English in my question. The reason I've added the cost estimation was for EdBeal that suggested that pumping the water itself would be cheaper, so I added my estimation to my approach. – Offer Feb 18 '21 at 13:51
  • @Ecnerwal - Thanks for your comment. Generally, I totally agree with your assumptions. In this case, my reason is not for making myself 'more clever'. There is one day a week I can't rely on electricity to give me the pressure, nor the water. Also, buffering and saving the pressure (air and water) - will make the electric engine (in my case - the air compressor) work much rarely than if I'd use it to push the water. – Offer Feb 18 '21 at 13:57
  • You're most welcome. The English edits come from a kid whose mother was an English major and whose father was just picky, so it's a habit. It's intended to help non-native speakers to learn, not to put them to shame. Your English is _far_ better than my Hebrew ever was (it _was_ passable, though). Since you don't include electricity costs, it's hard to make a comparison, plus the up-front purchase price will probably pale in comparison to the long-term running costs of the 2 alternates. – FreeMan Feb 18 '21 at 13:57
  • Why does the tank need to be pressurized? You put a fill valve like a toilet on the supply side, and you either A) put a pump on the output side to your house, or B) tee the output with a pump that only feeds your shower, or C) put the tank on a 5 meter tower on the roof. These things are common all around the world, you can just go buy them. Pressurizing the storage tank is an interesting engineering question but I don't see why you would do that from a home improvement perspective??? – jay613 Feb 18 '21 at 15:21

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Offer, I do not know of a regulator that will do what you want but it could be done with solenoid valves. You discuss a 200L pressure tank this is 52.8 gallons Even with low flow shower heads that’s not much shower time. my wife 3 daughters, 6 granddaughters would think that is just about right for 1 shower. (A 2.5 gallon shower head for ~20 minutes). You state that electricity is not reliable, but air compressors also use electricity and as someone that has cheap small volume air compressors to high volume compressors these are energy hogs they are not an efficient way to boost your pressure. A pressure tank is usually used to provide a buffer to the system and reduce the start cycles on the pump. It is obvious you do not want to hear this advice and I will accept the down votes but air over water in a dynamic system will be more costly and more prone to failure. Just as an example I can give dozens of water pump designs used in hundreds of millions of homes but not one example like yours.

Could your idea work, sure it could, but it would require an air compressor and solenoid valves to control the tank pressure for a very limited amount of water between recharge cycles.

A small pump 1/2 horse power possibly smaller could provide the flow & pressure from a holding tank. This is what people in the US do when they have low flow water wells, they pump into a open cistern or tank not pressurized, a pump at the tank pressurizes the system usually comprised of a small pressure tank to reduce the start cycles. A large plastic tank to hold water is not very expensive. I live in a zone that has abundant ground water. There are some areas that the water is deep or they don’t have a good flow so a holding tank or cistern is used not air over water. It is a good question and I up vote it for that but I do not think it is economically viable.

Ed Beal
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    A gas (petrol) powered air compressor is an option, but probably not in the $200 range the OP spec'd. – FreeMan Feb 18 '21 at 15:42
  • I had not thought about gas powered compressor, but thinking along those lines a gas powered water pump would be less expensive but that is an idea with unreliable electricity. – Ed Beal Feb 18 '21 at 17:07
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This is how it's done in New York City. No air pumps, no water pumps, just gravity. There are complexities in taller buildings that may not concern you if you have only 4 floors in use.

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jay613
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  • Jay, there is a water pump to push the water up. Every foot of elevation is 1/2 psi but this is an “open tank” not sealed or not a pressure tank. almost every city in the US has one. Since the op doesn't have the height a booster pump would still be needed. – Ed Beal Feb 18 '21 at 17:10
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    Agreed. Equally though there are lots of 6-story buildings with no storage tanks. It obviously depends on the details but OP's situation might be able to use a tank on a pedestal on the roof. Can we agree that a pressurized storage tank for an apartment is more of a Rube Goldberg project than a Home Improvement one? – jay613 Feb 18 '21 at 18:24
  • Jay I was biting my tong trying to not invoke Rube, lol, – Ed Beal Feb 18 '21 at 18:58