SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

What is the point of all this? If the ground is frozen, nothing is growing, and moisture is hardly relevant. Also, if any liquid of sub-freezing temperatures did manage to get into the soil, it might do damage to plant roots.

The first issue I can see to comment on is protection of the water supply. Because you are putting additives into the water, the water source MUST be protected by an RPZ back-flow preventer or by an air-gap.

As for protecting the pipe, there is flexable pipe. It's less prone to damage from stepping on, but more prone to damage from a sharp tool. Of course you could just bury the pipe like any normal irrigation install as well.

An for the check valves, they make ones that can be installed inline with the pipe, some can install on the underside of the pop-up, and some pop-ups come with check valves within them. For example, I used Rainbird pop-ups for my lawn irrigation. Since it was on a hill, I bought all pop-ups with integrated check valves except for the one pop-up that would be at the highest point of each circuit.

But the one problem with the pop-ups, to the best of my knowledge, 12" is the MAX size for these pop-ups. If you need 2' pop-ups, the best thing you might be able to do is build 1' tall boxes where you want the heads and install 12" pop-ups on the tops of these boxes... but then what's the point. You might as well just install a 24" box with either a fixed head on-top, or a standard 4" pop-up so the actual spray head retracts for protection.

The thing I would do is to build 24" tall boxes with fixed spray heads, but the bottom of the boxes need to be hollow with some sort of flexable hose or tubing connected to the spray head. At the point you want to connect the 24" box to the underground pipe, install an in-the-ground valve box (one with a 6" round cover) with a connection point. The idea is that when you want to setup for the winter, you bring out the 24" box, lay it on its side, pop the top on the 6" underground box, tuck the top inside the hollow 24" box, connect the hose to the connection point, stand the box up over the open valve box. At the start of summer, lay the box on its side, disconnect the hose, replace the lid, store the box til winter.

The only tricky parts will be what sort of hose connection? You might be able to use standard nipples on the spray and use hose clamps to clamp a piece of garden hose to it, and then use standard garden hose connections inside the valve box. If $$$ isn't a big issue, they make some quick-connect pieces that are designed with the idea of a burried (inside a box) hose connection.

Why not keep everything above grade? Spray nozzles can be placed along a pipe, with the sections joined by unions. Break it down and store it away, when not in use.

No need to build your own caps when valve boxes can be easily purchased:
6" Round Valve Box
Notice in the drawing where it has a spot for the burried pipe to enter? All you have to do is dig your trench for the pipe, then where you want to place one of these boxes, dig the trench a little wider and deeper (deep enough to have about a 1" to 2" layer of crushed rock to support the base of the valve box. You simply want the depth of the box so that the lid is flush with the ground.

The most difficult part is POTENTIALLY the connection inside this valve box. The problem is that most irrigation plumbing is designed to be installed once, not repeated connect/disconnect. The most common "quick connect/disconnect" is designed for garden hoses... but then garden hoses rely on washers to prevent leaks (and usually not very well in my experience). However, if you want to go that route, there is a PVC to MHT fittings (Male Hose Threaded, most PVC threaded fittings are MPT or FPT - Pipe Threaded). So the thing you could do is get sets of garden hose quick-connect male/female pieces, install the PVC to MHT and hose quick connect in the valve box, then use garden hose repair parts and a single garden hose to make a bunch of short garden hoses to run from the valve box to the sprinkler. If you go that way, you even have the option of just using old-fashion garden sprinklers on the top sides of your boxes (but you wouldn't get very good performance unless you're using HUGE underground pipes and enough pressure to feed the number of sprinkler required).

Quoted from "mxquattro"

Oh, yes I could run the plumbing above ground, but its kind of a high traffic area, so we prefer to keep it underground.

If the project is a necessity, then the traffic will have to go around. It will not exist all below grade, no matter how much you might want it to. The reason for this is simple ~ you require sprays from a height of 24 inches above grade, and no one makes a 24-inch popup of any sort whatsoever. Maybe you should rethink your choice of location.