Irrigation: How to calculate water flow, etc.

[Aquaman]

It's about .433 psi per foot of elevation.

Or to approach it from another angle: 1 psi = approx. 2.31 vertical feet of water. Also, it doesn't matter what the diameter of the tank is. Believe it or don't.... a 2" pipe 100' high full of water will read the same pressure at ground level as a 100' tall water tank. Okay, I'll quit being a know-it-all now.

 

[RobertN]

A quick Internet search indicates drippers work in a range of 8 to 60 psi. Design tables seem to start around 20 psi. Assuming a minimum design pressure of 20 psi your water source has to be 20/.433 or 46 ft higher than your first dripper.

At 10 psi the water source would have to be 23 ft higher than the first dripper. 10 psi would probably be impractical as you would need large pipe to minimize pressure loss or just use a couple of drippers.

I would think you would want pressures higher than 20 psi.

A tank will only increase water pressure if you use a pump. It will actually decrease water pressure as you can only fill the tank as high as the water source. As soon as you start using the water in the tank the level will drop below the water source and the water pressure will be less.

You can increase water pressure with a tank if you place the tank above the water source and pump the water up...as my neighbor does with his well/tank/drip system.

Zeuspaul

Drips use low flow, low pressure.

When I did landscape work, I always put a maximum 20psi regulator on drip lines. The barb fittings are not made for pressure; pressure will blow them apart. Too many time I went out to fix irrigation, and found drip, or spray head sprinklers, with too much pressure. Regulate the pressure, and most problems went away.

They do not need a lot of flow either, so friction loss on pipe is not a big consideration. Most drip emitters are 0.5 or 1.0 gph. You can add up all the emitters you have, and see how many gph you come up with. If you have 50gph of emitters, and only 25gph of water, then you double the time to get enough water to your plants.

Be sure to filter. Filter filter filter filter, and filter some more. And, clean the filters regularly. A big problem with drip systems I have seen is lack of filtration. Those little orifices on drip emitters clog pretty easy.

Check your drip yearly, and adjust for plant growth. I have seen a lot of drip that was installed nicely when plants were put in, but 2 years down the road, the plants are larger, and need more water.

Buy the good stuff. We always bought at an irrigation supply house. The stuff at the box stores is thin, small diameter, and does not hold up well in the long rung. Run a minimum 3/4" line. The 1/2" stuff is useless...

 

[Rara Avis]

You also need to take into consideration friction loss and cross-section of piping...

Here is the text we used in the Fire Service...Has all the math you need to do your problem...

http://www.ifsta.org/html/catalog/36492.htm;jsessionid=1197014635.8795

 

[blueberryman]

Hiifarmer, You might try this link . Alot of good info here. Good people to work with too.

Welcome to TRICKL-EEZ Company

 

[saltman]

Sounds like RobertN has the solution. If you ever feel the need for more pressure you can simply put a holding tank just down from your spring and just below that put in a pressure tank. My pressure tank can be adjusted to put out 100psi. I was told that it can do this on as little as 5psi going into the tank as long as you have the water volume.

 

[J_J]

I have a spring at the top of a hill that I've dug out. I'm currently getting 1/2 gal per min. I want to irrigate a small orchard that I plan to build lower on the hill.

Suppose I have X feet of drip line that's at least 20 vertical feet below the spring. How do I go about figuring out what size tank I'll need to achieve the necessary water pressure to feed the system? Any good websites or books on this sort of thing?

Since pressure is based on the weight of the water, I figure I need to ensure a certain height for a column of water above the outflow -- and this includes the height of the tank and the vertical height of the pipe from the tank. I think. Of course this changes as the tank is emptied. Hmmm...

I'm trying to do back-of-the-envelope calculations to determine whether it's feasible to even use my spring. Thanks for any tips or pointers.

I think I would calculate the amount of water that you need to irrigate what you have , and select a water tank to hold the water, and attach a low pressure pump to the tank, and run it through a pressure regulator designed for your drip, sprayers system. A digital timer works great for this if you have different zones. This is assuming that you have electric power close by, if not, a small engine driven pump would do the job.