Renewable Energy Questions/Discussion > Renewable Energy Q&A

Water pressure question

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madlabs:
Hi all,

So, at my neighbors place (which will be off grid) the have their well about 20-30' above their building site. For the sake of this discussion, let's say 20'. That would make 8.6 psi pressure at the build site. So, if we took a large diameter pipe, say 4", ran it down the hill to the build site and then choked it off to a smaller diameter, say 3/4", there would be an increase in pressure, no?

I have been looking around for a calculator to figger this out, but no luck. I'm guessing that it's out there and I am not searching for the right term.

Thanks!

Jonathan

halfcrazy:
If it was gravity flow than I would say no but I may be thinking incorrect.

Ryan

tomw:
Bigger tube means more flow.

Pressure is essentially the "column" of water above the outlet and effectively the same, regardless of the outlet size. Oversimplified but that is how it works.

Sorry to blow your idea out of the water [pun intended], but that is my understanding of it.

Tom

oztules:
It's the weight of the water that creates the pressure you feel.

The weight of the water in  20' of 4"  vertical pipe is more than the weight of water in a 20' @ 1 inch pipe.......

But we measure pressure as a per unit area amount..... so even for the 4" example, we take only 1 square inch of surface area at the bottom and look at that column of water only.... all the other square inches of cross section are the same........

So the diameter of the pipe counts for nil.... it is the height of the water that determines the pressure in ....lbs PER square inch...... more square inches gives you more lbs, but the same lbs/square inch..... which is your pressure.


Clear as mud..............oztules

madlabs:
Drats! But part of me still thinks why isn't it like when you put your thumb over the end of a hose, you trade some volume for some pressure. Don't folks decrease pipe size in micro hydro to increase velocity?

Thanks, and forgive my ignorance!

Jonathan

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