Sprinker system installation questions

1) How deep should I dig my trenches for my lateral lines? I live in the Seattle area; I'm not sure how much of an issue freezing is.
2) I notice that sprinkler head bodies come in varying heights. I'm just going to be watering a 350 sq. ft. lawn (no shrubs) and I'm wondering what height I should purchase? All of my radii are 10' or less.
3) Double-check valves seem to be sized to fit a range of sizes. I'm considering the following Conbraco unit; will it accomodate my 1-1/4" PVC mainline? http://www.sprinklerwarehouse.com/1-Conbraco-Double-Check-Valve-Assembly-p/cdc40-105-t2.htm
4) I had a plumber tell me that I could bury my double check valve in a valve box underground. All of the models I see online, however, seem to require them to be mounted a foot above the ground. Are there types that can be buried? I don't mind putting forth a little extra money/effort to protect my potable water.
5) Can someone recommend a Seattle-area retailer that carries sprinkler heads, valves, and accessories that are of higher quality than one finds at Home Depot?
Thanks for any guidance!
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If you install an automatic drain valve at the one low spot of each line it shouldn't be a problem. The pipe does need to slope towards the drain so all the water can drain. A foot or so is good.though.

You want the head to be able to get above the plants and other obsticles around it.

http://www.sprinklerwarehouse.com/1-Conbraco-Double-Check-Valve-Assembly-p/cdc40-105-t2.htm A vacuum breaker in the supply line before the control valves and above the ground piping would probably be a cheaper solution.

Are they really that bad?
Bob
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Freezing isn't an issue. In areas where it freezes the system are either made to self drain or else blown out with air before winter. I'd suggest if your going to trench, go 8". That's about the depth of a rotor head. And that way the pipe will be deep enough so that you can aerate the lawn and not run the chance of hitting a line. The pros use equipment that basicly pulls the pipe and in hard soil areas, they probably wind up half that depth in many spots.

Should be app info on the manufacturers websites that give a guide.

Don't know, fitting size should be on the spec sheet.

How does burying it do anything to protect your water? The backflow devices I've seen on systems have been mounted above ground, where the pipe exits the building. Seems the easy and logical way to do it to me, unless there is a specific problem. Usually, they are just hidden by shrubs. I'd check the local code as they may have reqts as to specific type of device, location, etc.

Here on the east coast, the local plumbing supply sells them. Check there or under irrigation supplies.
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United pipe and supply. They are all over the area. Bury six to eight inches works in Portland. Hell, my home water supply is that deep and it has reached 9 degrees here a few times.....no problems. The thing is, you don't have days of freeze. You have a night or two of it....not enough to really freeze underground.
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Ken-
I've installed & maintained several sprinkler systems (my own homes, rental properties & my relatives homes) over the past 30 years.
I have a vested interest in a system that works......I've got to maintain it & make any changes needed to make sure it works.
I use Toro 570 series 3" pop-ups for lawns, http://www.toro.com/sprinklers/fixedspray/index.html
available at HD; I'm just now repalced Toro 570's installed in 1980
I use Champion (red brass) automatic anti-siphon valves w/ unions brass/brass units not any cheap plastic acutators http://www.championirrigation.com/HTML_Pages/Cat_ASVs.html get the "classic" model they last longer
I have some units in service for 30 years, the acutators have been replaced only once in that time; the valve bodies should last nearly 100 years
red brass due to the high copper content (80-85%) and has a life expectancy of 50-100 years..
I've been through a number of timer models & manufactures ......Now I use the Toro ECx 8-Zone Sprinkler Timer, I've got four operating systems as I type.
It's does everything I need a timer to do; it's intuitive, reliable & you can get them on Ebay!
http://www.toro.com/sprinklers/timers/ecx/53333.html
cheers Bob
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Thanks everyone for your responses.
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Ken wrote:

I would be inclined to have the lines a little deeper, particularly near the heads. Over the years, soil shifts and you may have to raise some heads to match the higher surface. Its a lot easier to raise a head by adding a riser than to raise the lateral line. To keep the head perpendicular, you have to either use a riser, or raise the lateral line for a foot or two near the head.

This depends on how short you keep your grass. A 3-inch pop up may not clear grass that is kept long, while it would be ok if you keep the grass very short.

http://www.sprinklerwarehouse.com/1-Conbraco-Double-Check-Valve-Assembly-p/cdc40-105-t2.htm
I would check around and find an irrigation supply house that will serve the public, and then choose a brand based on what is available. In my neighborhood, neither HD nor Lowe's carries irrigation equipment (although Rainbird lists Lowe's as a source) and some years ago when HD did carry irrigation equipment, it had the same brand name as what the pro's used, but what they were selling was plainly a less sturdy product. I've had very good results with Rainbird, but I think all the manufacturers have a pro level product that is good, so finding a good supplier would be my main consideration.

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