closed loop water turbine

I have in my thought cage and idea that I'm not sure is possible, but figured this was the group to chat about it. Would it be possible to recycle water that has run through a turbine back up and around again using a ram pump, essentially creating a closed loop water engine? Has anyone heard of such a thing? I've done some searching on the tubes, but haven't found anything yet.

Another half-baked idea is to somehow introduce grey water and filtration into the equation. It would cease to be a closed loop, but maybe better for different applications.

Ram pumps work, by utilizing the mass of the moving water, to temperarily raise the pressure to the point where water can be pumped uphill.  But, the efficiency is only a few percent, meaning only a few percent of water flowing downhill is actually pumped back uphill.  Basically, a very LARGE volume of water falling downhill can push a very small amount of water back uphill.  A closed loop system would run for a little while until the water in the upper tank is drained, and then it will simply grind to a halt.

Your implication is that it would be an engine that could somehow be applied to producing useful work.  You simply can't get something for nothing. The laws of physics is not on your side.

Sean Bahr wrote:I have in my thought cage and idea that I'm not sure is possible, but figured this was the group to chat about it. Would it be possible to recycle water that has run through a turbine back up and around again using a ram pump, essentially creating a closed loop water engine? Has anyone heard of such a thing? I've done some searching on the tubes, but haven't found anything yet.

Another half-baked idea is to somehow introduce grey water and filtration into the equation. It would cease to be a closed loop, but maybe better for different applications.

Micheal Quick is indeed correct, and this in no way negates what he says.

But in the hydroturbine world you can get a little bit extra out of the flowing water via the venturi effect. When I worked at a fairly modern dam, a 16 megawatt dam built in 1989, it used this principal. No different then how a carburetor necks down, then goes big again to get a little bit of siphoning effect, a dam with horizontal turbines can gain a little in output.

That dam further got more efficiency by having variable turbine pitch. That was, the turbine  blade could by spun on its axis so that it was flatter, allowing more contact with the water to get the generator turning from a dead stopt, then would adjust itself to a more angled pitch at higher speeds as the need for torque reduced and it just needed rpm to keep the generators locked in with the grid. There was a bell curve that showed the ideal turbine pitch to generator megawatt output, and that was so the most power was produced from the least amount of water flow.

I think it would be hard to build that variable pitch turbine blade into a home-built microhydro project, but it had amazing attributes. At full headpond I could pull 16,000 kilowatts, or go down as low as 175 kilowatts. Whatever the river was flowing, we could match.

Well explained by Michael. A closed loop system designed like that would only run for a very short amount of time. Even if you were trying to pump water from a flowing creek up a hill with a ram pump to run a turbine, you would have much better efficiency to use all of the water flowing in the creek to turn the turbine and transmit the power uphill. Ram pumps lift around 20% of the water that flows in to them (best case scenario).

Thank you all for the replies!