I am totally new to all this and I am trying to learn as much of this as possible before I spent $$ on trial and error. I have read irrigationtutorials.com over and over and picked up a book on sprinkler systems. I have completed dimensions and approximation of where I want to water and after checking with local code, my next step is to select a backflow preventor. I have noticed most installs on this forum uses a vacuum breaker (PVB), but since my highest sprinkler head sits in a retaining wall (sits pretty high off the ground), I have chosen to use either a Reduced Pressure Backflow Preventer or a double check backflow preventor since elevation of the BP would not be an issue. Now which would be preferred and cost-effective (R.P. unit -or- Double check)? My county requires that it be ASSI code 1013 or 1020. I have researched these brands: Febco 860/860U and Wilkins 975XL Does anyone have any other suggestions? Brands/model I was also wondering why Febco is cheaper to Wilkins by over $60 Does anyone suggestion going with a Double-Check Backflow preventer, if so why?