# can water pressure differentials provide power

If you pumped water into the top of a water tower and vents were added to the top of the water tower to separate the tower reservoir from the pump to make two different but related systems. The tower would feed a tube of with internal turbines every few feet or less. the flow rate of the pump would have to be adjusted such that the rate of flow out of the turbine tube would be as close to as possible but slightly less than the the flow rate coming out of the pump so the tower would always be full and providing pressure to the turbine tube.

the reason that this would make energy is because the shier volume of water in the tower would provide potentially hundreds of times more the the pressure provided by the pump allowing the water to be pushed through potentially hundreds of turbines with the flow rate still being the same. this would create allot more power then is put in! Would this work? if not why not?

I also realize that at this point it wouldn't be much of a water tower but I thought it would make it easier to picture, my main question would be if you created one of these for purely generating power would it work?

• it costs energy to pump the water up to the top of the tower in the first place, doesn't it? so any energy you get out of your turbines is energy you already paid for. the way to beat the system is to catch rainwater in the tower and generate power by letting that water fall through your turbine. that way you do not have to pay energy to pump it up to the top of the tower. Commented Dec 20, 2017 at 20:37

the [sheer] volume of water in the tower would provide potentially hundreds of times more the the pressure provided by the pump.

Nope. The volume has nothing to do with it. The pressure in a body of water depends only on the depth at which you measure it. The pressure at the bottom of a giant tank, full of water 30m high would be exactly the same as the pressure at the bottom of a skinny, vertical pipe full of water to the same height.

The pump always has to supply enough energy to the water to overcome the force of gravity and reach the final height. The work required for the pump to do so is always going to be the same or less than the work you get out of the turbines.

This is conservation of energy.

When you factor in efficiencies of the pumps and turbines, you will always get less power out of the water than you required to pump it up to that height in the first place.

You talk about the extreme volume of water that you could have in the tower, and how that could provide more (something, I assume either pressure or energy) than the pump has to provide. The thing is, this isn't true. The pump has to get all of the large volume of water up there and then also keep the flow rate going. Also, the higher the water tower, the more backpressure on the pump; therefore the greater pressure differential the pump would need to provide to overcome this additional water.

You can't get more energy than you put in; and if you could, we would have some serious issues in the universe.

Sure, you can turn potential energy into work, that's what dams do.

But fundamentally, you can never get out more energy than what you put in, period, full stop.

• just curious as to if you can explain why I would not be able to in this case, what would prevent me from getting more power out? Commented Dec 20, 2017 at 19:32

As stated by others, you can't get more energy out than you put in. In a cost per unit of energy situation you could realize a cost benefit if the pump operates during periods of cheaper energy (electricity) input. Your water tower setup could then,conceivably, generate energy at a higher net profit per unit than the cost of input. This method is actually widely employed.