Trying to plan a pressure-tank + air compressor for raising home water pressure

Question

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.

Answer 1

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.

Answer 2

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.