TheBackShed.com

Forum Index : Windmills : water presure

Author

Message

trout
Newbie

Joined: 29/11/2014
Location: Australia
Posts: 24

Posted: 11:26pm 02 Dec 2014

Copy link to clipboard

Print this post

Hi yas I would like to know how much presure I would get if I ran a 50mm poly pipe up my hill to a elavation of 50mtrs above the outlet level then sent a constant flowof water down that pipe? I know there is a simple equasion but idont know how to do it.cheers

davef
Guru

Joined: 14/05/2006
Location: New Zealand
Posts: 499

Posted: 01:10am 03 Dec 2014

Copy link to clipboard

Print this post

There will be many charts around the internet to tell you what the static head is for 50mtrs.

The quantity that you are really interested in is what the maximum power that you can extract under your conditions. As you try to increase the flowrate, beyond a certain amount, the power available will start to drop. The term used for this is called the "choke" value. From memory for a 50mm pipe this is around 3L/s, which I used in my previous reply.

Of course you can run it at less than the "choke" value, but then you have to be careful you don't run into another problem, running at less than the "critical flowrate". If you have any high spots in your penstock you need to run it at greater than 1.2L/s, or you get airlocks.

Edited by davef 2014-12-04

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 03:16am 03 Dec 2014

Copy link to clipboard

Print this post

I only know the calculation using feet, so 50m = 164Ft.

Now the 50m needs to be TVD or True Vertical Depth, and not 50m over a steady incline of over 50m.

Weight of water * 0.052 * TVD (in ft) = PSI

8.34 x 0.052 = 0.4337
0.4337 x 164 = 71.124 PSI

So for a TVD of 50m with fresh water you would have 71 PSI of hydrostatic pressure.

But remember your flow rate will change due to friction loss of the pipe over distance, but the pressure will remain constant, unless friction loss is greater than flow rate.
Although the pressure will always be the same when the end of the pipe is closed off, or often said as burst pressure.

Pete.

Sometimes it just works

norcold

Guru

Joined: 06/02/2011
Location: Australia
Posts: 670

Posted: 11:45am 03 Dec 2014

Copy link to clipboard

Print this post

The metric formula for pressure for water is simply P=hx9.81. Therefore you have 50m H x 9.81 = 490.5 kPa(4.905 bar) but for a quick top of head figure just x by 10 for metric. For imperial / by 2 when using head in feet and pressure in lbs/sqinch.ie 50feet = 25psi roughly, tis good enough for us.

This of course is static pressure. SG does not needed to be used in calculation with water simply because water has a SG of 1.ie multiply a figure by 1 or divide it by 1 as example.

We come from the land downunder.
Vic

trout
Newbie

Joined: 29/11/2014
Location: Australia
Posts: 24

Posted: 11:43pm 09 Dec 2014

Copy link to clipboard

Print this post

Thanks so much for ya yelp just need to buy the pipe and finish building the smart drive power station.who wants some free power ?

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 12:53am 10 Dec 2014

Copy link to clipboard

Print this post

Quote who wants some free power ?

Dont count your chickens too soon, as what you think you might get will be likely lower than what you actually get.

Good luck.

Pete.

Sometimes it just works

Print this page

To reply to this topic, you need to log in.