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

When it comes to 3/4" pipe, that's sort of a minimum size when it comes to irrigation. 3/4" pipe will likely be fine if you are simply feeding a drip irrigation system, or if you are watering a small yard. Otherwise, you might run into too much pressure loss depending upon the water flow and distances involved. You will need to look into pressure loss charts so that you can see how much water pressure you will loose through 3/4" pipe for the distances and water rates you are looking at.

I personally do not have any experience with poly pipe. I just recall from reading irrigation books that poly is more likely to get damaged from instilation or something running over it later. But that it's also more forgiving should there be any water in the pipes during a freeze.

I used PVC myself, and from what I recall, the price difference between 1" and 3/4" was pretty darn small that I considered it worth it to spend the few extra dollars up front to make sure I had plenty of capacity (because of pressure losses in water flowing through pipes, larger is always better). It wasn't until you got into 1-1/4" and above PVC that material costs jumped significantly.

As for depth, unless there is some over-riding building code you must follow, 10" to 12" depth is standard (though some will try to get away with 8"). That's plenty low enough that arrators will never harm it. And again, in general, the deeper, the better (more protected) it is. But obviously the deeper, the greater the cost (in either money or work).

Using 3/4" pipe might lead to too much pressure loss depending upon the distances you are having to go. Basically, as far as irrigation goes,,

The idea of using 1" everywhere is that it makes the job easier, especially if someone unfamilier with the design is helping. It completely elliminates the possibility for errors involving installing the wrong size pipe.

As for glueing individual pieces, that sounds like PVC to me. That's the way I did it. Attually I did use both 1" and 3/4". But I was installing everything myself, and I was using 1" pipe for lawn irrigation and 3/4" for feeding drip irrigation. But I wanted the smaller pipe when possible because I was installing multiple pipes in one trench (a huge risk if anyone of them ever breaks, but that's why I burried them at least 12" deep, used sch40 PVC for latterals, and initially backfilled with sand and/or screened dirt).

Generally speaking, the most common way to work with PVC is purchasing the pipes in 10' lengths and glueing them together on site. And it doesn't matter if it's 3/4" or 1", it takes just as long to glue either one, and it can take a long time. After all, the process requires:
1. Cut the pipe to the length needed. Debur if needed
2. Use primer on pipe and fitting.
3. Wait for primer to dry.
4. Apply glue to pipe and fitting.
5. Insert the pipe into the fitting, twisting as you go.
6. Hold the pipe and fitting together for about 30 seconds (otherwise the wet glue tends to push the pieces back apart).
7. Do it all over again for the pipe on the other side of the fitting.

Sure, when you have a large number of glue joints to make, you can find some efficiencies, like priming several pieces at once so that by the time you prime the last one, the 1st one is dry. But beyond that, it takes a few minutes on every single joint. Those few minutes build up over time.