1

I have a big elevation drop from one side of my house to the other. I must choose one of these sides as a take off for hose spigot-to-PEX which I'm going to lay under ground toward my garden about 600 linear feet away.

If I take off the North side, it will have to go uphill the whole way to the top of the garden area and then downhill as it heads into the garden area. If I take off the South side, it will go downhill most of the way and then uphill into the garden from the south side, all the way to the future garden spigots.

I'm worried about the water, which is of course under pressure like a normal hose would be, would perform poorly if I chose the South route and after it going uphill the whole way. But maybe being under pressure it'll be fine no matter what? The South route is preferable for other reasons. But it would be a disaster if I put it in and it didn't work.

Thoughts? Does it matter which way you route from the house to a garden for water flow?

Update:

I decided to test it by running a garden hose the entire length along both paths (yes... 600 feet of chained hoses!)... the pressure at the end felt the same either way. So it sounds like the route doesn't matter. It was definitely diminished (I could stop the flow with my thumb), but usable I think (for drip line), and that's with 5/8" with various leaks along the way. The PEX I'll be laying in the larger 3/4" and of course won't have any leaks. Hopefully, that will be enough to power the drip lines?

2
  • 2
    The biggest issue you'll have at 600 linear feet is adequate pipe size that the "pressure under flow" isn't ludicrously low due to dynamic head (pipe friction losses) on top of elevation head loss. If your area freezes, you'll have to deal with how to drain it for the winter, which can be more difficult with low spots in the line, or require additional drain valves.
    – Ecnerwal
    Apr 28, 2023 at 0:16
  • Thank you, this is helpful. I put an update in my question. How much improvement do I get using 3/4" ?
    – Paul W
    Apr 28, 2023 at 0:52

1 Answer 1

2

Making the simplification that 600 feet of 5/8" hose is equivalent to 600 feet of 5/8" smooth plastic pipe, this head loss calculator (one of many available on the web, which may give varible answers (and some will be in feet of head, not PSI) states

  • 7.9 PSI for 3/4" and 19.2 PSI for 5/8" at 3 GPM flow.
  • 20.4 PSI for 3/4" and 49.4 PSI for 5/8" at 5 GPM flow.
  • 38.0 PSI for 3/4" and 92.2 PSI for 5/8" at 7 GPM flow.
  • 73.5 PSI for 3/4" and 178.4 PSI for 5/8" at 10 GPM flow.

(which more likely means you won't get 7 or 10 GPM out of 5/8" and 10 is dubious for 3/4" unless your supply pressure is quite high.)

1" at 5 GPM is 5 PSI. At 7 GPM it's 9.2 PSI. At 10 GPM it's 18.1 PSI

So, whether it works for your drip system (I think mine wanted ~12-25 PSI at input) depends on how many drip emitters are on at once, and the resulting flow rate, as well as what the pressure at the house is, and how high the hill is (static head.) In practice if more emitters are on at once than the pipe you choose can support, they will flow less, and may flow more unevenly as well.

Unfortunately controllers and/or valves are far more expensive than drip line, but one method to balance the pipe flow rate .vs. cost of larger pipe to flow more is to have more valves and smaller drip zones that run at different times. That's also possible to do manually with cheaper valves, but becomes a chore .vs. having automation manage it.

A pressure gauge is rather more informative than "stopping the flow with your thumb." I can do that at 50PSI or more with a bit of determination.

When shopping for pipe, note that it is very common for 300 or 500 (or sometimes 600, and 1000 is way more than you need) feet to cost much less per foot than 100 feet. If it's really 490 by the shorter route, a 500 would do the job with no couplings along the way.

5
  • Thank you, this is helpful. I definitely have been planning on multiple timers and drip zones and only doing one section at a time. I have better numbers now. The south route is the one I'm leaning towards and it's shorter, at 490ft. There's an 18ft rise in elevation. The hose bib on the house measures 7 GPM. I don't know the PSI (I plan to buy a gauge tomorrow and check it). The various calculators I've found and that you linked to give me a PSI loss of between 25 and 30 PSI for the 3/4 pipe, plus another 8 PSI for the rise in elevation. So between 33 and 38 total PSI loss.
    – Paul W
    Apr 28, 2023 at 2:39
  • If I need a minimum of 15 at the garden, then my home had better be at 48-53 PSI or higher. Am I doing this right? I see that upgrading to 1" has a huge impact and would give me around 20 more PSI. But it's also a lot more expensive.
    – Paul W
    Apr 28, 2023 at 2:41
  • 1
    I note you mention using PEX - for outdoor cold water work plain old "Black Polyethylene Well Pipe" (not crosslinked, which is the X in PEX) is quite suitable (as well as being sunlight resistant where it comes out of the ground) and may cost less. If you are on city water it may not be something you are familiar with. As demonstrated in the example numbers, you can reduce the flow and the resulting pressure loss due to pipe friction drops significantly.
    – Ecnerwal
    Apr 28, 2023 at 10:40
  • It will be under constant pressure during the non-freezing part of the year, and will need to last year after year hopefully without needing repair. Is black poly as good as PEX in that regard?
    – Paul W
    Apr 28, 2023 at 10:59
  • 1
    Absolutely. It's been used for well pipe that is under constant pressure for more than 50 years. And a quick check at my local supplier shows 1" 100 PSI-rated (it also comes in higher pressures with thicker walls at higher prices) at LESS than 3/4" PEX. And PEX does degrade and fail when exposed to sunlight...Plus, it uses insert barb fittings and hose clamps (use 2 per barb, clamp head oriented opposite per pair) [so, 4 per coupling or elbow, 6 for a Tee] rather than a big fancy crimper you'd probably have to buy or rent.
    – Ecnerwal
    Apr 28, 2023 at 11:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.