Replacing old galv irrigation pipe

tns1

I'll be replacing about 100ft of old galv irrigation main with pvc. The old stuff is only partially buried and even though the top surface looks fine (no rust), the underside has pitted severely where it contacts the soil. A good lesson in 25yrs or more of corrosion.

The water service looks something like this. A main meter and shutoff in the street, a service main with shutoff on the property, and separate branches to the house and outside irrigation (fruit orchard).

.................................../---M--X2--house
-M-X0---svc main---X1--|
...................................\-------X3--irrigation----X4---->more

The service main, X1 and the house branch are already pvc. For now I am just looking at replacing the first 100ft of the old galv irrigation branch and valves. I'll worry about the rest of the irrigation pipe another day.

I plan on burying the new pvc only enough to cover it (6" max) to keep the branch connections simple and avoid conflicts with septic and other
pipes.

For valves X3,X4 I was thinking of replacing the old brass globe valves with the inline pvc glue-on type, similar to what is used for X1,X2. Rather than have these sit at or below ground in a box, I was going to have verticals stick out of the ground for the valves. The valve body would be up a foot on a vert. or short horz section. Not only does this make access and repair easier, it provides for thermal expansion of the long pipe. Damage of the riser is not a concern.

This run includes a couple of T branches and 3 or so hose bibs risers. For all these I was going to T off horizontally and transition to smaller threaded connections for use with either galv, copper or rigid plastic.

Sound reasonable?

tns1

The service main is 1.5" pvc but this is reduced to 1" for the 75ft run to the house and also for the few hundred feet of irrigation pipe. What size is recommended?

There are some postings about anti-backflow devices. Now is the time for me to add one if needed. Anyone know what is used in so cal?

tns1

According to the water district here, there are no requirements for residential water to have any type of anti-backflow device. The big box stores do carry one or two but only up to 1" pipe. They do carry some inexpensive pvc check-valves up to 1.5", so maybe I will add one of those on the irrigation line.

kenmac

here , all irrigation must have back flo preventer/ check valve to ensure potable water doesn't get contaminated

TheEplumber

I don't see any big isues with your plan. But do consider a backflow device on the irragation branch. Pipe sizing will vary. It depends on your minimum pressure. elavation change and water demand at each outlet.

moondawg

If you ever use any sort of chemicals on your lawn, please do. Without one, any chemicals that touch any part of your irrigation devices will get sucked into your (and your neighbors) water supply.

downunder

What flow rate do you need for your irrigation? I work for a parks department and we use 3/4" on all normal irrigation zones- everything except for the sports fields. But I doubt you are running a system of several hundred gallons per hour.

Yes there have been several threads regarding backflow devices. If it is required by code in your area, then by all means do so. But I am still waiting for someone to explain to me how the whole neighborhood can be contaminated by fertilizer on the lawn when you have to have a negative pressure on the line (think of sucking [siphoning] gas out of a car instead of pumping it in.) This can only happen if there was a significant break in a water main, a major fire nearby and the fire department was drawing water for the fire truck, or something similar AND you have the irrigation head submerged so that it can not suck air and break the vacuum. That's why they also call anti-siphon valves "vacuum breakers."

IF you are using one of the fertilizer injectors that has a hose that you put into a container of concentrated fertilizer solution and it siphons the concentrated solution into the flow stream, AND there is a break/negative pressure event on the water main, AND you could somehow be running an irrigation system with no or very little water pressure, then I will concede that this danger exists. Otherwise, to quote Chicken Little, "...."

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TheEplumber

Where did the 5 acre pond go?
http://www.bacflounlimited.com/Cross...on%20Info..htm

downunder

Sorry, I don't understand the point of the pond since these are two completely different situations. The water was pushed from the pond because of a 20 psi negative pressure (90 pushing 70). Similar to what happens with a thermal expansion tank on a hot water heater-HWH pressure pushing against water supply pressure.

So the pond water was pushed back into the city water supply. Nowhere in that article is the identification of any contaminants from the area being irrigated having been "sucked" back into the water system, simply that the pond volume was pushed back into the city water supply. See that- the pond water was pushed into the city water supply with a higher pressure pump. Contaminants were not sucked from the ground. In the case of the pond, YES, a backflow preventer was called for. I could even agree to a little maintenance and checking it once in a while. Why am I even bothering to answer this?

See how easy it is to take a little bit of "truth" and confuse the issue?

On second thought, I do understand the point.

__________________
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!