Since you say zone 5, I'm guessing Wasatch front, right? I'm not sure what the frost line is, but it's not very deep. Compared with Illinois, we have really odd weather. We have late frosts in the spring and early frosts in the fall, but it doesn't really get cold in the winter (rarely below 20F and I don't remember seeing it get to 0 since I moved here in 93). I do turn off the water to the irrigation at the end of the fall and drain the water (but I've never had it blown out). I think my sprinkler lines are about 6 inches deep and I've never had a problem due to frost. I had a neighbor who installed his own and didn't put the pipe deep enough and he was repairing pipe a couple of times a year. I've only had a pipe burst once and that was self inflicted (poorly chosen location for a new rose bush). Most of the irrigation systems here are installed with PVC and use little or no copper. Given your description of your current system, I think it might be worth replacing it rather than trying to repair it. Since some of the pipe is improperly laid (and you don't know for sure what is done right), you'd almost have to dig up everything to get it all right. And if you're not getting good coverage, you need to figure out a better design anyway. This is about the worst time to try to do this kind of a job, since it's so hot and if the sprinklers haven't been working correctly, the soil is likely to be as hard as a rock (unless you live someplace like Sandy and have sand instead of clay). But it's also about the worst time to try to leave the lawn unwatered (unless you're a wacko like me, trying to grow a native lawn and even I have had to water once and will have to water again this week). I think there are places that will help you design a system and there may be websites, also (I think Rainbird has a site that will help with the design). The biggest suggestion I can make is that you should use gear driven sprinklers for the rotating heads, not the impact sprinklers that seem to be more popular. The gear driven heads are more reliable and apply water more evenly. And they're nearly silent. I've still got a couple of impact sprinklers, but as they go, I replace them with gear driven heads (and I've replaced a couple that were still working because the gear driven ones are so much better). If I were installing a system now, one thing I would include is a probe to determine when the soil has dried to a depth of at least 4 inches. Most people set up their sprinklers on a schedule and end up watering too much. There are systems available that connect to probes and will only water when the soil dries out so that you don't water too often. Believe it or not, the biggest problem most lawns along the Wasatch front face is too much water. That's an odd problem for desert conditions, but it's because too many people water improperly.

Dul, Pressure is the dependent on how many outlets or sprinklers are in operation. If you have only one riser running then it will receive all the system pressure. The flow rate will be dependent on the cross-sectional area of the pipe and pressure. Systems are designed to handle the way the irrigation is set up knowing the flow rates of all the system irrigation heads and the overall system pressure. You could calculate what you can do by knowing each component's flow rate and pressure drop. But most people do things by trial and error. Which way do you want to go. To calculate the design, you need to some homework. For starters, the system's total flow rate and pressure. Would you know how to find those? Aloha

If you have pressure concerns, you would be better served by spending the extra cash and upsizing the valves and pipe. If would be money very well spent. All Wet

You will need to check your pressure, if it's too high, it will blow your bubblers out of the poly. But yes, it can be done, using a Female Pipe Thread swivel fitting, in the size of your poly tubing. Most common being .700. Drip irrigation should be around 25 psi. You might get by with a little more tho.