These sprinklers are great. I use them all the time in designs. I think their distribution center is in Irvine, CA. They're concealed residential sprinklers are the smallest I've ever seen and the sprinklers are inexpensive. The 9'rule stinks but you get used to it.
Don't worry about the provision to shut off the supply to the domestic line.
The automatic shut-off device is only beneficial in dwellings that share the same underground supply. If you have something that shuts off the domestic supply, then you don't need to include the extra 5gpm.
For...
If its a stand-alone system. Put the PRV downstream of the tee branching off to the fire line.
On a multipurpose system, you'll need to have a prv for a bypass line. (That is , unless the water softener/filter can handle the full flow of the system.)
The prv has to be set low, but not too...
The 2010 edition of NFPA 13D has a new section that deals with this issue.
6.1.4 The stored water requirement of 6.1.2 or 6.1.3 shall be permitted to be a combination of the water in the well (including the refill rate) plus the water in the holding tank if such tank can supply the sprinkler...
13D gives some guidelines for homeowners in the appendix.
A4.2.1
If it's an existing system, I would make sure they haven't made recent changes to the floor plan that would have a negative affect on the sprinkler spacing or spray patterns.
13D systems arent required to have a calc plate so I...
