Water Pressures

812harleys · Nov 17, 2007

Hi there, I have been doing google searches and looking in books to find a formula for calculating water pressure and can't seem to nail down what I want to know. Is there a good, simple formula to calculate this?? EXAMPLE;
I have 1000' of 3' pipe laid with about 15' of gradual fall in that distance. The end of pipe isn't for another 1000' and I have an 8" turnout at that 1000' to service irrigation to a farmer. I need to know what the pressure is at that 8" turnout. I have found a jillion formulas for calculating pressure loss but I need to know an approxamate starting place. Is there any formula to be used for an example like this? There will be a couple of turnouts above this one and several downstream and I would like to be able to calculate these pressures. :beatsme The inlet to the pipe is a settling pond off of an existing open canal with at most 10' depth.

digger242j · Nov 17, 2007

So, what you're looking for is what's known as the "hydraulic head", right?

I'm no engineer or mathematician, but this looks like a good place to start, (if you can read Greek

) :

http://en.wikipedia.org/wiki/Head_(hydraulic)

I'm not saying it meets your specification for a "simple" formula, but I'm not sure there is one...

812harleys · Nov 17, 2007

Thank you, I haven't seen this one and I am finding out there IS no simple formula.:Banghead :bash

ointhead When(or if????) I find the answer I will post it!

zhkent · Nov 17, 2007

1 foot height equals .43 psi.
About 2 1/2 feet for 1 psi.
15 feet of fall x .43 = 6.45 psi.

zhkent · Nov 17, 2007

woops, missed the other pipe being 10 feet deep.
10 x .43 = 4.3
4.3 + 6.45 = 10.75

Your total head pressure is 10 or 11 psi.

JDOFMEMI · Nov 18, 2007

That will give you the static pressure. If you want the pressure while flowing, it adds a whole new level of difficulty, like friction loss, and others

Squizzy246B · Nov 18, 2007

10m of head (roughly 33 feet) = 1 atmosphere or 14.7 psi....ask any diver......thats Scuba diver of course:cool2

812harleys · Nov 18, 2007

Thanks guys, I came up with 6.45 static pressure @ 15' of fall and thought it was crazy. I have been getting into the formulas for flow rate, resistance, darcey equations and it is very involved. I too forgot about the 10' at the pond. I am sure it will change greatly when flowing up throught the 8" pipe as well. I used to dislike engineers until I started doing this, now I have a different respect for that side of operating. Digging it is the fun part!:usa I sure am glad you posted that ZHKENT. Head pressure is all I am going to need for now. Thanks to everyone as well, it is really great to have a place like this forum to learn!!:notworthy

33horse · Nov 20, 2007

Water Pressure/Travelling Sprinkler

I went thru the same headache and mine was complicated doing research on pumps. I have a 3 in well that free flows 90 gallons a minute. I needed pressure. Without electricity the only alternative was gas. After much research I found there at hundreds of gas powered pumps but none could deliver enough pressure. I ended up finding a Mitsubishi at Northern Tool that delivers 90 psi at 1000 feet. $500. The initial test came as a neighbor decided he wanted a large above ground pool. He was going to fill it via a shallow well pump for his house. I figured it would take him 5 days and probably burn the pump up from all the cycling. So I offered to run a 2 inch line 1200 feet from my well. It took 4 hours to glue the pipe and 2 hours to fill the pool with 16,000 gallons of water. Wow!!! With the pump running holding the pipe in the air the water had a 30 foot arc. Unbelievable.
Still faced with laying the pipe for irrigation (primarily Sprinklers) We found the cost to install sprinkler heads in enough density to cover 10 acres was costly. SO we did some shopping for some alternatives. We are researching Travelling Sprinklers. It's a water powered machine with a big sprinkler head and Hose reel. Hook up the water at a spigot, pull the hose out 300 feet, and turn the water on. As the water flows the machine pulls the hose and sprinker back. Having horses this is a terrific idea for us as we don't have to be concerned about exposed sprinkler heads or a horse stepping on sprinklers.
Before we order one of these Traveling Sprinklers I thought I'd ask around to see if anyone had first hand experience with them and any problems they might have had. This is the website and the Brand I am considering. AND American Made !

http://www.rapidrain.com/howitworks.html

812harleys · Nov 20, 2007

Thats a good looking traveling sprinkler. I have had experience with the tractor style that follows the hose and had good luck as long as you don't hit mud, then it will spin out and turn over. It would pull alot of hose for such a little thing but the one on the website you posted looks like a better deal. I like northern for engines and all. I bought a 5.5 horse briggs and stratton for a replacement log splitter engine and only paid $219.00 with shipping and it was the newer style motor, instead of straight up and down the cylinder is about a 60 degree angle. Another one on the other side and it would resemble a Harley!! Someone told me that the older style motor isn't even available new anymore due to emissions and all.

JDOFMEMI · Nov 21, 2007

33horse said:
I went thru the same headache and mine was complicated doing research on pumps. I have a 3 in well that free flows 90 gallons a minute. I needed pressure. Without electricity the only alternative was gas. After much research I found there at hundreds of gas powered pumps but none could deliver enough pressure. I ended up finding a Mitsubishi at Northern Tool that delivers 90 psi at 1000 feet. $500. The initial test came as a neighbor decided he wanted a large above ground pool. He was going to fill it via a shallow well pump for his house. I figured it would take him 5 days and probably burn the pump up from all the cycling. So I offered to run a 2 inch line 1200 feet from my well. It took 4 hours to glue the pipe and 2 hours to fill the pool with 16,000 gallons of water. Wow!!! With the pump running holding the pipe in the air the water had a 30 foot arc. Unbelievable.
Still faced with laying the pipe for irrigation (primarily Sprinklers) We found the cost to install sprinkler heads in enough density to cover 10 acres was costly. SO we did some shopping for some alternatives. We are researching Travelling Sprinklers. It's a water powered machine with a big sprinkler head and Hose reel. Hook up the water at a spigot, pull the hose out 300 feet, and turn the water on. As the water flows the machine pulls the hose and sprinker back. Having horses this is a terrific idea for us as we don't have to be concerned about exposed sprinkler heads or a horse stepping on sprinklers.
Before we order one of these Traveling Sprinklers I thought I'd ask around to see if anyone had first hand experience with them and any problems they might have had. This is the website and the Brand I am considering. AND American Made !

http://www.rapidrain.com/howitworks.html

I can't remember the brand, but I have used a traveling big gun sprinkler before. It came with a 600 ft 6" hose, and you could run the hose from a pipe in the center of the field back to one end. The traveling unit had a winch with 1200 ft of cable attached to a winch with a 4 speed truck transmission powered by a turbine n the piping. Thats right, the water pressure pulled this along. We were feeding it with I think about 300 gallons per minute at 50 to 55 psi. This gave us a radius of somewhere between 100 to 150 ft. You use the transmission to control the speed, thereby regulating the amount of water on each area.
This worked very well. We pre watered a 300,000 cy job with it after renting it from a local farmer. The unit weighed several thousand pounds, plus dragging 600 ft of 6" hose full of water. The winch had enough pull to drag a 580 Case unless it was dug into the ground.

I would like to get my hands on another one.

atgreene · Nov 22, 2007

So you have a total head of 5' and you need to know the static pressure or residual? Static pressure is with no water flowing, residual is what is left when flowing water.

In the fire service we have a rule of thumb that for each story, add 1/2 a pound of loss for gravity. Likewise, when pumping down hill, you gain 1/2 a pound of pressure for each 10'.

Thus, regardless of pipe size, you will always have approximately 5lbs. of pressure from a 10' head.

For friction loss, you need to know flow (gpm) to know what you have for friction loss.

It sounds like you need Bernoulli's Equation to compute what you need, but I'm not sure without more info.

Water Pressures

812harleys

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digger242j

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zhkent

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zhkent

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JDOFMEMI

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Squizzy246B

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812harleys

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33horse

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