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malibu jim

Active Member

1

Thursday, November 17th 2005, 5:43pm

Supply Line

An old friend hired someone to renovate his front and back lawn with new sod, install front and back sprinklers and do some cement work. I guess the guy screwed up the cement so bad that he was asked to leave. The cement work has been completed by someone else. The 1st installer started to run pvc pipes for the sprinklers, but I really can't figure out, what kind of plan he had. Anyway, I plan on tapping into the service line (1") in the front lawn, and running it to the back, under a sidewalk, about 6 ft wide. The previous installer had run 2 ea 3/4" pvc pipes under the sidewalk. Would it be better to (1) split the 1" line from the service line, thru both 3/4" lines and then rejoin them in the backyard; (2) just use 1 of the 3/4" lines and then go back up to 1"; or (3) attach a 1" line to one of the existing 3/4 lines with an adapter and try to drive it under the sidewalk? Realizing #3 is probably the most desireable, but requires the most work.

Wet_Boots

Supreme Member

Posts: 4,050

Location: Metro NYC

2

Friday, November 18th 2005, 1:33am

If you don't need the extra line, you could use both of them. If you use only one, just figure in the added pressure loss in your design.

johnmaag

New Member

Posts: 4

Location: USA

3

Thursday, March 2nd 2006, 8:45am

I have a somewhat related question on a supply line.

I am having a second water meter installed dedicated to the sprinkler system. The water meter will be 1" and my static pressure is 50 PSI. Since I have my choice of what size Supply line therein is the question. "How big of a supply line is too big"? I will be running 1" supply lines in each zone.

My Scott's Sprinkler System Design book mentions using 1 1/4" off of a meter and I noticed in their table I gained 2 GPM more using 1 1/4" supply line off of a 1" meter instead of 1" supply line off of a 1" meter but the table does not include using 1 1/2" supply line off of a 1" meter. This led me to believe maybe 1 1/2" was too big.


Tom

Supreme Member

4

Thursday, March 2nd 2006, 11:25am

It really depends on the length of the service line and what flow your zones are designed for. I would guess with the limited info you gave that a 1.25" mainline would be fine, however..............

A few years back I installed a commercial system that was designed with a 1" meter and 1.5" mainline. The mainline was about 900' in length.


johnmaag

New Member

Posts: 4

Location: USA

5

Thursday, March 2nd 2006, 11:40am

I guess I should have been more clear. The main line will only be about 20-25 feet long but I want to use the largest pipe size I can to maximize GPM without getting so big that my pressure is compromised. In particular, I would like to use 1 1/2". It appears that you have used that succesfully. I was concerned that it may cause my pressure to drop.

Wet_Boots

Supreme Member

Posts: 4,050

Location: Metro NYC

6

Thursday, March 2nd 2006, 12:10pm

At 25 feet in length, you won't gain anything measurable with a supply line larger than the meter. For a supply line that's 40 times the length of yours, you do get a return on investment for a larger line diameter.

How large a property is this? Such a short supply line would seem to imply a smaller lot.

johnmaag

New Member

Posts: 4

Location: USA

7

Thursday, March 2nd 2006, 2:19pm

It is a small lot.

The Scott's book has this table:

Water-Meter Supply-line GPM@50 PSI
1" 3/4" 12
1" 1" 19.5
1" 1 1/4" 23.5

So I figured bigger might be better if not too big plus a 1 1/2" Backflow was slightly cheaper than a 1 1/4" backflow. Are you disagreeing with Scvott's information?
1"

Wet_Boots

Supreme Member

Posts: 4,050

Location: Metro NYC

8

Friday, March 3rd 2006, 4:14am

Is there some iron-clad requirement to do all the watering in a very short time period? Why go spending money you don't have to? Depending on the water pressure, one can probably do just fine on a standard 3/4" supply line and a 5/8" water meter, especially with that short a run. Do a calculation on the time it takes to apply 1/3" of water for the entire lawn, based on different flow rates. If the lawn is small enough, even a flow of less than 10 gpm will do just fine.

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