Question
Question
My water meter is 3/4 and my supply line is 3/4"(60PSI)
I will install a Reduced Pressure Backflow Preventer to3/4 pipe in and 3/4 out and than to  1"  Jar Top Valves and
1" poly pipe.
I have one 1" (Watts Series 800M4 FR)
Is it OK to use 1" or I must buy 3/4".
Any suggestions and help would be greatly appreciated.

Answer
Roman,

This is a common concern to most people designing/installing their own sprinkler system. Typically, reducing pipe size in the laterals is only beneficial to you financially. In other words, pipe sizing is used to save money. The logic behind that is: as you travel further down a line with heads on it, you lose volume. Why pay for a bigger pipe size when you don't need/have that much water? Contrary to common belief, reducing pipe size will not increase pressure!

In my opinion, unless you have a huge system, the financial benefit that comes from pipe sizing does not justify the installation headache that comes from purchasing and trying to keep track of multiple kinds of  fittings, pipe, etc.

In your case, with the info you provided, you will do well by running a 1" main line and 1" laterals. I couldn't quite tell if your backflow was 1" or 3/4", but if it is 3/4", just use a 3/4" x 1" female adapter at the inlet and outlet (don't forget your unions before hand!) and you will be able to run 1" all the way to the valves. Also, make sure you don't have any runs of pipe shorter than 20 feet (then you have a velocity issue and water hammer may occur).

Last thing: may I suggest using a different type of valve than the jar top? In my experience, I have never had any luck with those things (leaky, bad performance, etc.). If you are purchasing these at a home center, I would suggest using Orbit 1" FNPT inline/angle with flow control (and use the angle inlet) or Rainbird DVF 1" instead. If you are buying at a sprinkler supply house, they will have the Rainbird PGA 1" (again, use the angle inlet). The PGA is the best residential/small commercial valve on the market.

Good luck with the system - let me know if there is anything more I can help with. - BC