Hydro electric power

The inlet pressure will be less due to the pressure drop from flowing frictional forces.

I agree with Guest basicly, the diameter of the penstock from the dam to the turbine inlet determines headloss during the 1,000 ft transit.

With that length penstock it may be adviseable to have a bypass valve that opens as the turbine inlet closes and then closes slowly to minimize penstock pressure rise.

Also remember to have a slow closing and slow-opening turbine valve or isolation valve at the powerhouse so you don't blow-up or collapse the long penstock. If it will be exposed to winter, you may have ice form inside the penstock which would break loose as the weather warms.

It is logical that friction losses will have to be deducted but the question may refer to a different setup than what I have in mind.

Falls like in free fall or just coming vertically down?

In an oversize down pipe the water may just fall and have the effective head much less than 100' and the turbulence will also have an effect.

Roseto you need to give us more detail. (pipe sizes, flow etc)

What type of turbine is involved?

If the flow of water is determined by a spillway the level of the dam and length of crest will have an effect.

What is the slope on the 1000' ?

It's true it will be less.But half way to the new location go down a pipe size or two this will increase the inlet pressure.try this web-link they have some useful information www.harringtonplastics.com

Why halfway?

According to that principle the highest pressure at the outlet would be obtained if the pipe is reduced right at the source.

Step 2 would be to start reducing once again and eventually end up with zero pipe diameter and infinite pressure at the discharge side.

A few people has spend a lot of cents to try this trick only to find out that the pressure is even less.

I used half way as an example. we had a similar problem with a water treatment facility. their was a lack of power to a remote location , the facility sat 1000 ft up from the river we were discharging the water into. so we placed a turbine on the discharge line about halfway and changed two pipe sizes on ower discharge line to get what we needed to run the turbine witch helped produce the rest of the power we needed for the facility. we knew how much we were discharging 1200 gal a minute, so we worked from there.Well in the history of the west they were able to use water pressure to mine for gold using this size down method and it worked quite well. they ajusted things to meet thier needs at times now we have to do the same, to make things work. to really give an accurate assement more information would be needed, like slope pipe size and volume. I have always found scale models work well in figuring out problem's like this with less cost.

When there is no flow, the pressure will be the same, in this case 100'. This is the design pressure for your pipework, valves etc.

When the turbine operates, available head will decrease according to the pressure drop in the pipe.

Basically, the bigger the pipe, the more of your initial head will be available to drive your turbine.

Restricting pipe size, as someone suggested will simply increase the head loss for any given flow.

Dear RONSETO,dt;01/03/2009

When you keep the same head level and shift the turbine further outwards from the dam,depending upon extended pipe length from first position ,there will be a pressure level differnce at the turbine [at the second stage position],which will reflect as reduced pressure.This is contributed by frictional losses in the extended pipe.This is a simple direct answer to your quiery..Beware of bernollis/chezy's/mannin's formulas ,if somebody is trying to explain,cause fewest people could have understood what is stated out of them.Give me yourfeed back.

S.Udhayamarthandan

My question was a general one, not an actual application. I am just trying to understand the underlying principals. In my example, everything theroetically is the same except for the turbine locations. Same pipe size, same head. Thank you all for educating me. So what I gather is: turbine output is indirectly proportional to the distance from the source and directly proportional to the head.

The formula is "KW = Q x H x eff./102"

"Q" is flow in litres/sec,

"H" is head in metres,

"eff" is efficiency as a decimal.

If the liquid is not water, then you need to multiply by the specific gravity.

If you use this to calculate the power required by a pump, instead of power output from a turbine, you need to divide by the pump efficiency instead of multiplying as you do for the turbine.

Obviously "H" is the head at the turbine after all losses getting there. Don't forget losses through valves and fittings as well as direct friction loss along the pipe.

Incidentally, you can use a centrifugal or axial flow pump in reverse as a turbine. The efficiency is roughly the same as when used as a pump. As a practical point you must make sure nothing is going to come unscrewed in the pump as it will be running in the opposite direction to that for which it was designed. An impeller unscrewing could be both embarrassing and damaging!

Your question triggered a chuckle, because I assumed that you meant that the water would be flowing down the river, after the dam, in the open. And in that 1000 feet, there would not be much pressure generated.

In that case, the water pressure would revert to almost nothing, because the top surface of the water is open to the atmosphere and all the pressure would be released. Then, the pressure that is exerted on the water by the atmosphere is equalized throughout the body of water, so it is equal in every direction.

You would find a slight increase in pressure at the bottom of the river, but only as much as the depth of water above the point where the take off for the turbines would be.

Picture putting the turbines into the flow of the water in the river, with concrete or other solid material blocking the flow in any other direction. Then there would still be some pressure. But the pressure would not be anything like that present at the outflow of a dam, which is actually holding back water and building up a tremendous head pressure - the weight of the water that is ABOVE the turbines.