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I am trying to build a little irrigation system where my water pump distributes the water into multiple outlets. I guess my question is how do I make sure the water flows evenly in all the pipes. I am using Pvc for everything. Any tips or suggestion would greatly be appreciated. Feel free to ask questions as my drawings are detailed. Thank you

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In general to get the water to flow evenly to all three outputs you have to ensure that all the paths from the pump to all three outputs is the same including length. In addition what ever nozzle or outlet opening you have has to be exactly the same for all three. To achieve this you will have to split the three outlet flow pipes before you get to the outputs. Something like this:

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I have made the above sketch to show how the paths from the split point to the outlets is the same length.

Now with that said if the distribution pipe inside diameter is large compared to the outlet nozzle and the pressure inside the pipe has a significant drop across the nozzle then the pipe path similarity and length as stated is less significant. What that means is that the manifold type outlets like you show in your drawing would work if they are close together and the pump maintains a head of pressure in the lines.

On the other hand if ends of the delivery pipes to the outlets is just an open ended pipe then the similarity of the paths will be important to achieve the same flow at each output.

  • Thank you for the response and drawing. Why does the middle line in your picture extend further out then the other two though? – JohnWang Jul 27 '17 at 23:22
  • @JohnWang - I already wrote why. "I have made the above sketch to show how the paths from the split point to the outlets is the same length." Some extra length is consumed in the upper and lower lines to go up and down. – Michael Karas Jul 28 '17 at 9:41
  • I agree with @Michael Karas for a system without flow / regulators all 3 pipes would need to be the same size and length. If regulators were added at each of the 3 they could be controlled as long as there is enough head pressure for the regulators to provide the same flow. – Ed Beal Aug 31 '17 at 14:51
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Can't be done in a pressurized system

This is a hard problem often encountered in engineering and there's no easy solution short of individual pumps or other rotating machinery. If you're looking for the magic bullet "how to fit your pipes so it works", there isn't one. If one pipe has more impedance than the others, it will flow significantly less.

If it was unpressurized, you could do it with a weir by segmenting the outlets. But if you need head of pressure to run a sprinkler system, the weir idea will only work if the weir is at a much higher altitude to give the head you need.

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You can do this in many different ways here is couple ways should be easy enough to do:

First option is creating a evenly distributed free low system. this would take a bit more effort than second option.

Use something like a barrel right at the end of the water inlet as a water container before distributing the flow in to separate pipes. Make sure this container is perfectly leveled the and attach your PVC pipes as exactly same height as individual outlets. give the pipes minimum of 10 degree down angle for the first 6 inches or so than you can divert them any direction you like as long as you don't go up :) This is the closest picture i could find to what i am trying to describe...

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If you could use a elbow pointing down at the end of the inlet pipe it would eliminate the extra natural flow would feed the outlet pipe directly in the same line with inlet pipe.

Second option would be much more simpler, just use a manifold like the one in the picture below and regulate the flow by adjusting the ball valves individually

The only set back for the second option is if you are using a submersible pump without a pressure vessel you will wear out the submersible pump much more quicker since the rotary vane type of pumps would not perform well in pressurized systems without a pressure vessel specially with long pipes.

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