This could be several things. Bruce already mentioned one. My next guess is that your backflow spring pressure is being overcome at seemingly random times (this is the backflow differential pressure). The pressure in the system has to drop some (drain off the system side) before any water actually starts flowing from the supply side through the backflow. The bigger the system, the more air in the system, and the smaller your test orifice, the longer this would take. Depending on the starting pressure on the supply side and system side of the backflow, this can take a different amount of time. You can usually watch this happen in real time by putting a gauge in on the #1 test port on the backflow and watch it along with the system gauge. I've had several suppliers and brand reps that didn't know that some of their backflow preventers have "low flow" check valves available, which I believe lowers the spring pressure to help alleviate this issue (this issue can also cause vibrating at low flows as the check valves quickly open and close over and over).
Sometimes the paddle temporarily catches on something. It doesn't take much. Take it out and inspect to make sure there is nothing inside the pipe that it is getting stuck on. Sometimes you will see a nick on the paddle to give you a hint. This next part is more common than something being in the pipe, but it only applies to the U-bolt version of the flow switches, not the screw-in type. When you put it back on, wiggle the flow switch so the paddle hits on either side so that you can make sure when you start to tighten it that the paddle is centered. Sometimes the paddle will barely catch on the edge of the hole that is drilled into the pipe (especially if the hole wasn't drilled perfectly perpendicular to the round pipe). NFPA does allow quite a big window of time for these to operate in, so what you are describing may be no big deal. The biggest issue is that they operate within the required time at all. If they didn't operate, that would be quite the cause for alarm (haha). Good Luck! Skyler Bilbo Wente Plumbing and Fire Protection Cell: 217-819-6404 On Mon, Oct 9, 2023 at 10:48 AM <kevin.far...@farreys.com> wrote: > we have 4 risers. 2 of them work perfectly, 2 of them have this delay for > the first test. any thoughts on why this only happens with 2 of them? > > _________________________________________________________ > SprinklerForum mailing list: > https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org > To unsubscribe send an email to > sprinklerforum-le...@lists.firesprinkler.org
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