Water tower: Why is all the water at the top?

[greypilgrim]

Hi.

Most water towers store their water in a huge container at their top. Why? Wouldn't it be easier to place the container at the bottom and just add a long, thin pipe upwards to create the hydrostatic pressure?

Is the problem that the container would need to endure too much pressure? Or that it might be difficult to keep the water level in the pipe constant?

 

[BvU]

How much water can the tower provide to the top floor of an apartment building, when there is only a few dm³ at the high pressure ?

 

[tnich]

Hi.

Most water towers store their water in a huge container at their top. Why? Wouldn't it be easier to place the container at the bottom and just add a long, thin pipe upwards to create the hydrostatic pressure?

Is the problem that the container would need to endure too much pressure? Or that it might be difficult to keep the water level in the pipe constant?

I have wondered about that, too. I think the point of the water tower is to provide a buffer between the pump that supplies the water and the consumers of the water. It provides a reservoir to maintain service while demand is high even with a relatively low-capacity pump. It also smoothes pressure changes resulting from changing demand and from the pump itself by maintaining a nearly constant water level.

 

[tnich]

How much water can the tower provide to the top floor of an apartment building, when there is only a few dm³ at the high pressure ?

Don't tall buildings usually have their own water reservoirs at the top?

 

[BvU]

I live in an area without skyscrapers, but I'm sure you're right. They are their own water tower.

 

[Grinkle]

Its a water capacitor. Without the tank at the top, the pressure will rapidly drop once the systems begins to demand water, or else the pump has to have enough throughput to keep the system going, basically meaning the pump would have to be sized to keep the pressure up. The tank at the top maintains the pressure as the system demand outpaces what the pump is able to replace, allowing for a smaller pump.

edit: I see @tnich already said all that ...

 

[Dale]

a relatively low-capacity pump.

I think this is the key. You can have a small pump that can operate continuously at capacity instead of a big pump that operates way under capacity most of the time but has to be over sized in order to meet peak demand.

 

[256bits]

Most water towers store their water in a huge container at their top. Why? Wouldn't it be easier to place the container at the bottom and just add a long, thin pipe upwards to create the hydrostatic pressure?

Certainly, it would be possible to do it that way. A small diameter pipe design with the continuous refill greater than that from the tank exit should stabilize the pressure. Of course when the power goes out, any water usage and the pressure drops drastically as the pipe empties. Kind of defeats the purpose of a having the tank at all as a reservoir.

 

[EmilioL]

So it doesn't have to be a pressure tank. Remember, the water system is pressurized.

Water arrives under pressure. Were you to store it in an open tank at ground level, you'd throw that energy away, Then later you'd have to pump the water back up to pressure in order to inject it into the municipal system. That's very inefficent. The water main pressure might be 60 PSI or higher. And you'd have to size the pump for peak demand. Bad design.

So instead, you take the incoming water under pressure and run it up a tower, simultaneously storing the water and converting some of the pressure into potential energy. You add a little energy with a pump to make up for friction losses--but this pump can run all the time, so it doesn't have to be sized to peak demand.
When you demand a big demand, the water will flow down like a cow peeing on a flat rock, so to speak. And as somebody mentioned, gravity works even when the power is out. Finally, an open tank is cheaper to build and less likely to leak than a pressure tank.

My house has a well and a pressure tank on the ground floor. It so happens that the air volume control valve (which has a float inside the tank that preiodically ges submerged) is currently broken. Water is not compressable, so you have to compress air. That means you have to control how much air is inside the tank (some tanks have bladders--adding yet another thing that can fail). Too much air, and you got no water. Too little, and the system is "waterlogged" and loses pressure
very quickly. I wish I had a water tower instead--much simpler

 

[EmilioL]

P.S. The tower acts as a pressure regulator, as well as storing water.. It's a form of standpipe.

There has to be either a tower or pressure tank in the system, because as I said, water is not compressable. Otherwise, the water in your pipes would act like hydraulic fluid in actuator: depress a piston in one end of the pipe, and the pressure soars until something moves (either another piston or blow-out through the side of the pipe). Most of us would prefer our water systems not to act like a hydraulic jack. :-)

Think of water as like marbles packed into a tube. Add one marble, and something's got to give. Take out one marble, and they all become loose. Now think of a vertical tube full of marbles (a standpipe): you can keep pushing marbles into the bottom, and the pressure goes up smoothly. Take marbles out, and the pressure goes down. Nice and smooth. No worries.

If you put a container of marbles (reservoir) at the top, you can achive a fairly uniform pressure, varying within a fairly narrow range.

Or you could put your marbles in a pressure tank with rubber diaphram holding compressed air, instead of an open tank on a tower. BUT the tank would have t be much larger--holding lots of air-- to get the same degree of pressure regulation.

The pressure tank in my water system operates over a 20 PSI range. At 40 PSI, a pressure switch turns on the well pump. Evey time you turn on the tap, the pressure drops, until it reaches 20 PSI, when the pressure switch turns the well pump on. The the pressure is always flutuctuating. That would be fine, except that we have a tankless waterheater, which shuts off when the flow gets too low. That propably explains the screams I often hear when guests try to take a shower... Funny how fast running water can go from 90F to 50F...