Pipe sizing for garden / irrigation "mainline"

[gmcinnes]

Guys, I'd appreciate your help.

How long a run can I do with 3/4" SIDR polyflex, starting with 60psi and still have "reasonable" pressure at the end?

Some context:

I'm adding some SIDR polyflex mainline to a large garden. There is some already in place by the previous owners. It's fed by 1/2" copper at the house and then a 3/4" polyflex over a run of 50' to a hose bib. Buried at 2'.

I'd like to add 300' - 500' of line, buried. It will have 8 hose bibs. I understand I can't supply all hose bibs simultaneously. I'm happy to manage usage so that only one is used at a given time. (Apart from anything else my well production wont stand sustained fully open valves even if the pressure is there)

The maximum elevation is about 25' above the well pump. The pressure at the well pump is 60 psi.

Am mad to think I can supply the last hose bib at the end of the pipe run with reasonable pressure if the other bibs are closed? If not, what would be the best approach to make it work?

I'm attaching a sketch. I hope it's legible. New work is in red, old work in black.

 

[oldVermonter]

FWIW:

I have about 500 feet of 3/4" poly line to supply my drip irrigation system and nine hose bibbs. The furthest bibb is about 400 feet from the house, and I get something like 180 gph at each bibb. However:

-I'm on a public water supply, which has very good pressure; and
-My garden slopes away from my house. The furthest point is probably 12 feet lower than the house bibb.

Of course, 1 inch line is more expensive. But if your well pressure is marginal, it might be well worth it.

 

[Sponsor]

 

[Reach4]

https://irrigation.wsu.edu/Content/Calculators/General/Pipeline-Pressure-Loss.php can help you estimate pressure drop.

 

[gmcinnes]

FWIW:

I have about 500 feet of 3/4" poly line to supply my drip irrigation system and nine hose bibbs. The furthest bibb is about 400 feet from the house, and I get something like 180 gph at each bibb. However:

-I'm on a public water supply, which has very good pressure; and
-My garden slopes away from my house. The furthest point is probably 12 feet lower than the house bibb.

Of course, 1 inch line is more expensive. But if your well pressure is marginal, it might be well worth it.

https://irrigation.wsu.edu/Content/Calculators/General/Pipeline-Pressure-Loss.php can help you estimate pressure drop.

How do I account for the 1/2" copper and 3/4" SIDR already in place? Are they linear in the sense that I can just add their pressure drop to the new work?

Best guess, is doing the new 350' of work in 1" worthwhile if the existing 100' work is 3/4"?

I can live with the extra cost for 1", I just want to avoid the extra fuss of reducers etc if not necessary.

(I'm not hugely concerned about total flow in terms of gph at the endpoint, but pressure to drive a drip system or be able to spray something with a hose at the endpoint is important. I realize they're related though.)

 

[Reach4]

How do I account for the 1/2" copper and 3/4" SIDR already in place? Are they linear in the sense that I can just add their pressure drop to the new work?

For the most part yes.

If you are willing to do a lot more work, https://www.pressure-drop.online/ can calculate drops for straight lines as well as various transitions.

 

[gmcinnes]

For the most part yes.

If you are willing to do a lot more work, https://www.pressure-drop.online/ can calculate drops for straight lines as well as various transitions.

Cool. I don't need anything so accurate. I'm just needing a sanity check to make sure my head isn't too far up my posterior. Seems like it will work out fine with 3/4"

I have a question about draining the line, but I'll ask it in a new post so that it's easier to search for someone looking later.