Some people will think this is over the top, but here's the process I use when expanding an irrigation zone, or re-tasking it.
- What's the static pressure at your house? (If you don't know, you should be able to purchase a gauge you can attach to your hose bib.
- How big is the pipe that feeds the irrigation system, and where is it located
- How big is the pipe after it leaves the valve
- How far is it to the place you want to cut, and how far to where you want to go
- How big is the pipe where you want to cut it
I can help sort what this all means, but essentially it give you a good idea of the approximate pressure and flow. Perhaps there are some easy changes you can make to increase one or both. From here, I'd do my head layout (remember that for best coverage, space head at their radius in a triangular pattern. To make it easy, I'd use the same type of nozzles, and pop-ups that you already have. Personally, I prefer to use 6" heads on lawns, not that standard 2" or 4". I find that over the years I have less maintenance to correct angle, depths, etc.
When laying out your pipe, try not to make large bends in the pipe. I know PVC is very flexible, but if you arch a pipe, and have to repair it, it's a pain. I prefer my pipes to have at minimum of 12" top cover. Keep the pipe sizing the same size as the existing, unless you have a compelling reason to downsize. Going to a larger pipe won't really help up, unless you're coming directly out of the valve.
When trenching, I prefer a 3" trenching shovel. I like to lay a piece of plastic down to put my dirt on. If you're cutting through grass, make strait sided blocks, about 1 ft x 1ft and pull them out so they stay intacted. Personally I prefer to keep them in the order they come out.
I mostly use a saw when cutting pipe. I will knock the files out as best I can, sometimes reaching my finger in to pull any remaining out. I was taught to use a knife to chamfer the inside and outside edge of the cut pipe, but I'm not really sure I believe it does a lot of good. Keep the fitting and pipe ends dry and clean. Take your primmer, and THOROUGHLY cover all surfaces what will be glues (inside of fitting, and outside of pipe), leaving no voids or blank spots. Add glue to the fittings and pipe (again, thoroughly cover with no voids). Then give the free piece a 1/4 turn from where you want it to end up, giving it a slide/twisting motion as you push it on. I prefer to hold for 30-60 seconds, then give it a quick cleaning with a paper towel.
I prefer to have my swing fittings be double swings so you get a full 360 degree rotation at each end. Here are two link to single swings, add a second marlex to each end to make it a double swing. Marlex are those little 90 degree elbows. They are designed to be the weak link. They are cheap, and easy to replace.
If you lay your threaded pipe fitting horizontal in the trench, and use a double swing you only have to dig a small hole to replace a broken fitting.
After you're done gluing let everything sit overnight, then flush the system really well (like a minute of flowing water). This would also be a good time to screw caps on the ends of all your swings (loosely at first) turn on the system to release all the air, then go and tighten all your caps down so you can test for leaks. I usually let the system run for 15 minutes before turning off. BE CAREFUL at this stage if you have unglued fitting they can pop out with a huge amount of force. After your test, carefully release the pressure from one cap before fully unscrewing the rest.
Install the pop-ups and nozzles and backfill. I like to start at the valve end of the repair and work my way as the water flows. I try not to leave any large rocks on the pipes. Typically I'll backfill a trench about 1/2 way, walk on it to compact it, complete the backfill. All the dirt should fit back in. If you want level grass at the end, don't compact the last layer of soil. Place the turf back in the order it came out, and use a 12x12 tamper to tamp it level.