Water Pressure

http://en.wikipedia.org/wiki/Darcy-Weisbach_equation

where p = pressure

h = head presure your case, its 100 ft

sg = specific gravity = 1

pressure = 100 x 1 / 2.31 = 43.29

This line I take it as 1" sch 40 pipe. wall thickness makes a difference.

This does not included loss through the line. which can have varying results due to the condition of the inside of your pipe, as well as length.

And do not confuse flow rate with pressure.

150ft is quite a ways from your barn, are there any elbows or fittings between?

It also depends that your tank is full.

Can not help you any more, hope you can use this.

phoenix911

The static pressure will be 100 feet of water or roughly 43 psi.

If you have flow through the pipe you will lose pressure due to friction.

What will be your flow requirement?

I get the suspicion that your tank is only being filled intermittently. In other words, the irrigation system is not tied directly into the stream which is 100ft in elevation. It sounds to me like you store this water in the tank, and every so often you refill the tank. But then you need to have it open to the stream during use. Either way, the previous posts nailed down the theoretical pressure which is simply the height of the water column (100ft). If you want, you can determine the frictional losses with the following formula.

Head loss = f x L/D x v^2/2g

Where,

f = friction factor (based on pipe material and condition as the other posts stated.

L = Length of pipe

D = Diameter of pipe (note: you must perform this calculation for each length of pipe that has different diameters)

v = fluid velocity

g = gravity (32.3 ft/s²)

The friction factor is dependant on Reynolds number and your pipe roughness – commercial steel pipe is 1.5 x 10^-4 ft. You'll need a "moody" diagram to find the Reynolds number.

The reality is that you need different formulas for different valves and elbows that are in your system. The formula above only considers straight pipe losses so it is not complete for your system. All the trouble you would go to calculate the pressure would still be only theoretical. I would personally just measure it – simple as that. If you haven't created the system yet, the calculation would be more useful to you.

Phoenix911 has given you the formula as:

where p = pressure

h = head presure your case, its 100 ft

sg = specific gravity = 1

pressure = 100 x 1 / 2.31 = 43.29

This line I take it as 1" sch 40 pipe. wall thickness makes a difference.

There will be 43.29 psi or 3 bar pressure BUT the line is running some 150 ft?

Estimated losses will be 40%. So The pressure will be 25-26 psi or 1.8 bar.

You 've mentioned nothing about flow. If you want the same flow (as 150 ft away) you need to increase pipe dia to get both flow & higher pressure 9due lesser frictional losses on bigger dia pipes).

There is a free book about this at drbratland.com, it is called Pipe Flow 1.