Loop Vs. Branches

14 years ago

Greetings. I am in the process of designing a home irrigation system which will water about 11,000 sq feet. BEcause of the location of the house, driveway and beds, it looks like I might have 5-6 zones? The water pressure is at about 55psi and because the house is over 120 years old with old water 3/5" mains, I am getting about 11gpm flow, hence the large number of zones?

anyway, I a getting hung up on the question of running a LOOP about the area to be irrigated, with valves coming off the main at various points to branch zone lines, or the "big plastic box of manifold" approach with branch lines all originating at a common point and radiating out to the zones? The furthest "corner" of my property (i.e. the furthest rotor head is about 130' from where the supply pipe for the system will come out from the basement.

I was thinking of running 1 1/2" PVC from the the house out diagonally across the property to that furthest point and distributing the zone branches from that 1 1/2" main, but then someone mentioned running a loop around the property?

Can someone share their view of the plusses/minuses of loop vs. branches? I guess the first is do I want two big honkin plastic boxes each with a manifold in the lawn, or 6 or 7 smaller single valve boxes? But esthetics aside for the time being, I'm more interested at this point in design?

thanks!!!!!!

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Comments (3)

mike1059
14 years ago
In your case I would recomend the loop layout to maintain
the max flow rate and minimize friction loss. In most cases the closer the valves are to the zone being waterd the better.
lehua49
14 years ago
tm,

There is no difference of pressure or flow in a loop system or mainline system if there is only one source. You have 11 gpm from your source. The flow rate off the loop system or the single mainline system will be divided by the number of lateral if each lateral's water demand is equal. Do not use more than 80% of your total flow rate in the design. Example: .8 x 11 gpm is 9 gpm divide by 3 lateral is 3 gpm per lateral. Use the number of irrigation heads on each lateral that equal 3 gpm. 55 psi is good pressure for a system but the total head loss on each lateral should not exceed 50% of the 55 psi(this is not likely). The loop system is less economical in that you use more pipe than necessary. The mainline system has valves and electrical wiring/Controller close to the source of water and electricity. The loop system may not. That is why the loop system is not used frequently in residential or almost none in commercial projects. If more flow rate is needed then a booster pump is used but that will make your antiquated water lines sing and your water company give you a call. I might suggest an irrigation designer do your design since your area is large and proper coverage is important. JMHO Aloha
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trkpoker
14 years ago
For that large of an area I would strongly advise trying to get a larger source of water. Meaning a larger meter. Call your local water company and see what is required to get a 1" to 1 1/2" meter line installed for irrigation use. Not sure about your area but here in South Fla a irrigation meter does not pay sewer charges for the water use. This amounts to about 1/2 of the bill. With a larger meter you would also have less zones because your flow would be better.

Lehua's 80% number is what I would have advised 10-15 years ago but in the last 10 years and even more so in recent years our local water companies have reduced our water pressure nearly 10 PSI. We are still in a very good PSI range BUT systems designed 20-30 years ago show problems with these changes. Shoot for even less IMO than the 80%....65-70% would be safer. Saying that it is even more important IMO to get a larger meter with a higher flow.

Something nearly always left out in these forum questions is what pressure you have while water is being used. Having 55 PSI really tells us very little. Having 11 GPM tells us something but still lacks the real info we need. We really need to know how much PSI you have when using X amount of water. This isn't the easiest thing for a homeowner to find out but a close enough measure can be made.

Place your PSI gauge on a water outlet on your source. Then discharge water. When your gauge is in the 27-38 PSI range check your meter to see how much water your using per min. This is a much better number to tell us how many heads (or more important how much water per min) you can run per zone.

Good luck,
Tom