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I recently ran some 3/4id poly pipe from my house about 300ft down a slight hill to my shop and garden area. I was not able to tie directly in to the underground pipe in the yard because my pressure regulator is under my house and I do not have a good way to get pipe out of the house underground. my solution was the put an irrigation valve box near a wall spigot and run a short, heavy duty hose from the wall to the valve box to feed the pipe. the inside pvc feeding the spigot I used is 1/2in. My issue with my flow at the garden is my flow, not the pressure. when I let pressure off and timed filling a 5 gallon bucket I calculated my volume to 4.2 gallons per minute, and my drip irrigation system will draw about 5.3 gallons per minute. My main question is trying to locate the bottleneck. its it mostly likely to be the 1/2 pvc pipe in the house? if so I can run a dedicated 3/4 line from closer to the house incoming line to the spigot, or would that cause the spigot to be a bottleneck? any help here would be greatly appreciated.

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  • I would suspect the spigot is already the bottleneck. Also does your spigot have a back flow prevention device?
    – NoSparksPlease
    May 12, 2021 at 13:46
  • I dont think it does, would it be best to install a check valve if I leave it on most of the time?
    – Zach McCann
    May 12, 2021 at 14:05

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300 feet of 3/4 poly is, itself, a restriction. That's a very long run for pipe that small.

Adding a section of 1/2 PVC doesn't help, but unless it's quite a long section, the 300 feet of 3/4 dominates the total dynamic head (which is what limits your flow.)

Is your incoming pressure so high that it would burst the pipe? If not, skipping the path through the PRV and house might be the easiest solution, as there would be more pressure head to start with, and you can put a garden hose or irrigation pressure reducer (quite inexpensive) at the end of the line, if needed.

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  • ok, I will have a pressure regulator for the drip irrigation system that is 12psi, but if I understand correctly that wont really matter if I do not have the water volume needed by the irrigation is larger than my flow through a hose.
    – Zach McCann
    May 12, 2021 at 14:52
  • would the best thing be to measure my flow from the hose at the house, and if it is significantly higher than what i am getting at the hydrant at the shop, then my problem would be my buried pipe correct? I am planning on putting a sink in my shop and have a pipe stobbed in there and capped at the moment is another reason why I wanted to be on the "down flow" side of the pressure regulator. I am not sure of the city water pressure or what kind of spikes they experience.
    – Zach McCann
    May 12, 2021 at 14:53
  • my parents had a huge headache last year when a faulty pressure regulator caused a sink supply hose to blow off and cause a lot of damage to hardwood and hvac system from running into the ducts. That causes me to be a little extra cautious on the water pressure.
    – Zach McCann
    May 12, 2021 at 14:53
  • You can put a second PRV on the shop, or in a suitably buried (assuming freezing might happen) box before the shop and garden at the far end of the pipe. Certainly reasonable to see what your flow rate at the input end is, yes. I once made the mistake of using 1/2" for a gravity (spring-fed, low source pressure) irrigation pipe, only about 100 feet. It was "educational" to say the least.
    – Ecnerwal
    May 12, 2021 at 15:00

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