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Tim57

New Member

Posts: 13

Location: Seattle, Washington

1

Monday, September 11th 2017, 12:00pm

What size main service line?

I am new to the forum....please bare with me and correct me when needed.

I have a 5/8" meter with a 3/4" brass pipe out with a 3/4" "T" fitting and a 1-1/4" poly pipe going to the house.

Pressure at the meter is 86 PSI with 19 GPM.

What size should I use from the 3/4" T to the back flow assembly and control valves. I believe I may need to reduce the pressure closer to 75 PSI so there may also be a PRV somewhere along the line.

I was thinking that the 5/8" meter would significantly hamper my system design by preventing the necessary pressure and volume. Please advise and thank you for your help.

Tim

Wet_Boots

Supreme Member

Posts: 5,147

Location: Metro NYC

2

Tuesday, September 12th 2017, 9:10am

The 5/8 designator is a little outdated, but it will remain in use to describe a water meter of specific length and end threads. One inch pipe will be enough to carry the irrigation supply. If you are in need of watering much more than an acre of lawn, you would be exchanging the meter for a larger size, that being one inch. (there is a 3/4 inch size, but most of its performance advantages have already become part of 5/8 meters)

Tim57

New Member

Posts: 13

Location: Seattle, Washington

3

Tuesday, September 12th 2017, 12:23pm

Thank you for your reply. I know your time is valuable and I certainly appreciate it. Could briefly explain the pressure/volume changes from the 5/8" meter at 86psi / 19 gpm, going a level 50' to the control valves via one inch pipe. Thanks again.

Wet_Boots

Supreme Member

Posts: 5,147

Location: Metro NYC

4

Wednesday, September 13th 2017, 8:16am

How many acres are you watering? And I do mean acres. 19 gpm is more than you probably want a 5/8 meter of any configuration to be supplying. Keep the flow to 15 gpm or less. Unless you got acreage or extremely sandy soil, you don't need the full 19 gpm. And is 86 psi the static (no flow) water pressure, or a pressure you measured at the outlet of the meter, while you observed the 19 gpm flow?

Do yourself a favor. Get your location into your user profile, so it shows next to your name. Answers to many questions can be location-specific.

Tim57

New Member

Posts: 13

Location: Seattle, Washington

5

Wednesday, September 13th 2017, 11:33am

I have about a 1/4 acre requiring irrigation. The 86 psi was measured at the water meter with no flow. My soil type is type 4 - sandy loam.

I'm just trying to determine the correct size of the main supply line from the meter to the irrigation system. I want to get the supply line in this fall and begin with the system in the spring. I just don't want to install a too small or too large supply line, backflow preventer, shut offs, etc. only to find later it wasn't right.

I'll be updating my profile. Thanks again for your time. :)

Wet_Boots

Supreme Member

Posts: 5,147

Location: Metro NYC

6

Thursday, September 14th 2017, 11:21am

You can do fine with one-inch pipe. If you want to "max out" your water supply, and there is 50+ feet between your point of connection and the valve manifold, you can upsize the pipe, but the added expense may never come back to you in savings on the installation cost of your sprinkler system.

What are you intending to use for backflow prevention? You are in an area where there are complications resolving the differences between old plumbing codes and current-day codes and practices. There are ways to proceed that will "please all masters."

Tim57

New Member

Posts: 13

Location: Seattle, Washington

7

Saturday, September 16th 2017, 11:42am

The local water company requires back flow prevention but they don't specify a type. I want to error on the side of safety so I am looking at a double check valve assembly or reduced pressure zone assembly. The two problems I'm having in selecting one is:

1. They're expensive and that's why I'm trying to pinpoint the right size supply line. My Rain Bird design specified 1-1/4" but of course -- the larger the back flow device, the larger the cost. If a 1" will work with my 86 psi / 19 gpm and < 1/4 acre to irrigate -- I would like to do that. Please advise.

2. There seems to be conflicting information between sprinkler warehouse and the back flow device vendor's regarding the installation of the DCV / DCA. Specifically, the requirement to install the device 12" above the highest sprinkler head. I asked for clarification from SW and they said the device could be in the ground....the vendor's all say they must be 12" above the highest sprinkler head. Please advise.

One more question please....what's best regarding the header supply lines and valve locations:

1. Place all valves in single location (manifold) and run the header lines to the valves the zone area or....

2. Run the header lines to the zone area valves.

Okay, maybe one more question...If I use 1" supply line, then I should use 1" header line and 3/4" lateral lines. Is this right?

As always, I really appreciate you for all your knowledge and help. Thank you.

Wet_Boots

Supreme Member

Posts: 5,147

Location: Metro NYC

8

Saturday, September 16th 2017, 4:48pm

Your backflow question touches on the potential conflict in plumbing regulations you face. Washington, like many states, imports their various codes from regional authorities. All across the country, the DCVA has been disappearing from lists of approved devices in the codes supplied by regional authorities.

I recommend you avoid the DCVA. The difference is that the other approved devices are rated as protection against toxic water backflow, and the DCVA is not. Toxic-rated is what you want for backflow prevention, because the is never any guarantee that old plumbing will be grandfathered in when codes change, and when they change, they always get stricter. There is a lot of field experience that backs up the stricter codes.

Quoted

603.5.6 Protection from Lawn Sprinklers and Irrigation Systems. Potable water supplies to systems having no pumps or connections for pumping equipment, and no chemical injection or provisions for chemical injection, shall be protected from backflow by one of the following:
(1) Atmospheric vacuum breaker (AVB).
(2) Pressure vacuum breaker backflow prevention
assembly (PVB).
(3) Spill-resistant pressure vacuum breaker (SVB).
(4) Reduced pressure principle backflow prevention
assembly (RP).
(5) A double check valve backflow prevention assembly
(DC) may be allowed when approved by the water
purveyor and the Authority Having Jurisdiction.

#5 is a concession we sometimes see, but definitely not always, to the old practice of using DCVAs. Many states changed the plumbing codes with a stroke of a pen, and their response to complaints of added expense to homeowners was tough luck, no grandfathering, because public safety was more important.


The 12-inch rule is important for devices that work on gravity, those being the PVB and AVB. If you are on flat ground, the above ground plumbing can be located near the home, convenient to the location of your controller.

One added wrinkle for the plumbing and backflow protection, is what is known as an Anti-Syphon Valve. The ASV combines a zone valve with an AVB. While it happens that having a row of ASVs is the most visible form of backflow prevention, they save you from having to pay an annual testing fee that goes along with any other form of backflow prevention.

As for plumbing and pipe sizes, think in terms of less than 19 gpm in your zones, and 1-inch pipe into and out of the zone valves. Reduction of pipe size at the ends of zone laterals is okay.

Double-check your math with these charts.

Tim57

New Member

Posts: 13

Location: Seattle, Washington

9

Sunday, September 17th 2017, 6:19pm

The more I read the more confusing this gets so I will try to keep this short and to the point.

Washington State specifies a RPBA for high risk systems and a DCVA or PVBA for low risk systems. Because I am safety conscious and I may add an auxiliary water supply (well) later on how does this sound to you:

Install a 1" RPBA above ground to keep the relief valve from becoming submerged and in an insulated enclosure to provide freeze protection. The drawing shows an Air Gap after the RPBA and I'm not sure if I need that also. I also plan to install it at least 12" above the highest sprinkler head if that's necessary.

From what I can see the RPBA is the safest way to go albeit more expensive. What do you think?

Thank you!

Wet_Boots

Supreme Member

Posts: 5,147

Location: Metro NYC

10

Sunday, September 17th 2017, 9:34pm

If you are on flat ground and you like your money staying in your wallet, you would use the anti-syphon valves, because an ASV doesn't cost much more than just a plain zone valve, and besides not having to buy and maintain a brass backflow prevention assembly, you also don't have to buy and install any valve boxes. The ASV is toxic-rated. If a vacuum breaker can feed water to a mortuary table, it's good to go for your lawn sprinklers.

You mentioned the high-hazard low-hazard dichotomy. Those are terms that are disappearing from codes. Nowadays, it's toxic and non-toxic. (and instead of trying to split hairs and paint with shades of grey, the entire outdoors is essentially considered toxic, and you plumb accordingly)

If you were intent on adding a well, run your numbers and see if it's worth the thousands involved. For a sprinkler system connected to both city water and a well, the city water must be protected by the RPBA (also abbreviated as RPZ). If nothing else, using an RPZ allows the downstream plumbing to be at any elevation, since it does not depend on gravity to work.

Also, from a practical standpoint, the vacuum breakers will always be more inherently reliable, because they work on gravity, and gravity is fairly reliable. The DCVA and RPZ work because somebody says so (and you may need to pay a someone on an annual basis to pass along their official say-so to the state/local authority)

Many parts of the country have the codes to require toxic-rated backflow prevention, but they don't enforce the recommended testing, and for them especially, they are best off with vacuum breaker(s) - either PVB or ASVs - install them at the proper elevations and let gravity do its thing.

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