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.
At .5gpm, I don't have enough pressure to push the water through drip hoses (I'm pretty sure). The tank would allow me to collect a large amount of water and generate pressure. (Hope you weren't asking a rhetorical question )
A tank wont change the pressure. It is the drop from the spring and whare you will use it that will make the pressure. a tank just stores more water. This is why they use water towers to store water. They pump water up as high as is needed to have the pressure they need.....Larry
Hmm. The height of the water in the tank obviously generates some water pressure. E.g. consider a water cooler. But I guess negligible compared to the height of the tank itself.
OK, so nix the tank size question. Given a vertical height of X feet, does anyone know how to compute the water pressure? Does the size of the pipe matter? I figure it shouldn't make a difference as long as there's enough source to fill the pipe.
mopacman said:
A tank wont change the pressure. It is the drop from the spring and whare you will use it that will make the pressure. a tank just stores more water. This is why they use water towers to store water. They pump water up as high as is needed to have the pressure they need.....Larry
If it's all down hill to the orchard then how about flood irrigation instead of pressurized drip lines.
Not sure how big your orchard is but we have a few small pecan orchards here that I flood. The one behind the house was the easiest. It's only one acre. I just made a little levy around that area and turn on the hose for a couple hours. It completely covers it with about 4 inches of water doing this instead of running the big water guns which takes a whole day to put that much down with 1/2 inch nozzles and 50 psi.
If you are able to just control the direction of the water I think it would be a lot cheaper and easier than trying to run drippers. I have those down my driveway for the trees and it's the biggest irrigation pain we have here.
First determine your flow demand, the number of emitters x the flow rate for each.
Then determine the total flow for a given watering period. The total flow would be the tank volume (potentially minus the make up of .5gpm over the flow period.
Determine pipe size to accomodate the gpm from the tank. Flow rate depends on pipe diameter & differential pressure (source /point of use). Always bigger pipe + slower flow & lower pressure drop. There are charts on line for flow rates per foot of different diameter pipes at different pressures.
Determine the pressure necessary to maintain the flow rate in your pipe. Raising the tank will create more pressure, larger pipe will create more usable pressure. Keep in mind this may require a pump to fill the tank, if so the pump can alternately pump from the tank to boost pressure into the discharge pipe.
Raising & filling the tank sounds like a great windmill application. Good luck, MikeD74T
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.
contact your drip line supplier...they will be happy to do the computations for you. they're probably sitting around with nothing to do this time of year anyway.
when i use t-tapes i use a 10lb pressure limiter. i am then able to easily irrigate 400 row feet. this is in increments of 100' per run. i could probably do more but thats limited by my setup.
