calculate water pressure?

Postby scotty49 » Sun Jul 29, 2007 1:27 pm

I am about to start renovating a dormer bungalow and want to add bath/shower on upper floor.Cold storage in attic with hot storage on upper floor. Currently no outlets upstairs so can`t fit gauge to measure pressure. Anyone know a mathematical formula for calculating likely pressure in gravity fed system based on head of water. This is a rural situation with private water supply therefore normal mains pressure is not an option.
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Simply Build It

Postby cookie85 » Thu Aug 02, 2007 8:32 am


A very basic pressure calculation can be done by doing the following. This will calculate the static head available from your cold water storage tank to your outlet.

p x g x h

p = density of water - 1000 m3/kg
g = gravitational constant - 9.81 m/s2
h = head of water available from tank to outlet (in meters)

This will give you your pressure in pascals. Which can be later converted to Kpa, or meters of head.

Does this help?
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Postby scotty49 » Thu Aug 02, 2007 7:03 pm

thanks for trying but,to be honest, I wouldn`t recocnise a Pascal if it jumped out the shower and bit me! Can I convert to more familiar measure like psi or bar?

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Postby Reynardine » Fri Aug 03, 2007 10:28 am

Elsewhere on this forum, 10 meters of head is roughly 1 bar.

Using the formula above for 10 metres of head and approximating gravity as 10 instead of 9.81 gives

10 metres of head x 10 gravity x 1000 density = 100,000 pascals = 1 bar

The conversion of pascals to bar by dividing by 100,000 is confirmed on this unit conversion website
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Postby DONFRAMAC » Sat Aug 04, 2007 12:19 am

As an "Old-Grey", educated in the era of O-LEVELS, we were taught that one atmosphere of pressure= 14.5 psi,= 760 mm mercury on a barometer, = 32 feet of water-gauge (head from a raised tank). This is the basis of one BAR, measure you see on weather-charts, and the millibar, which is one thousandth of an atmosphere of pressure.
Pascals and newtons did not complicate my life until I went to Uni., just at the same time as nanometres and picometres supplanted angstrom units !!
I hate metrication and all other arbitrary obsolescence, and still remember the confusion old folk experienced when our coinage was decimalised --- home-helps were suspected to be theives.
Heaven help us if we get the Euro.
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Postby scotty49 » Sat Aug 04, 2007 1:45 pm

Many thanks to all contributors for replies. I now have a clearer understanding of pressure calculations.
Thanks again
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