I agree with Matthew the only way out of this one is to manifold the riser and come off with a new system so you don't get messed up with the old system.
It was back in the 1980's when I designed a good amount of gridded dry systems and I myself never had a problem with trip times.... all you had to do was use your head a little.
For example a side feed grid without a feed main connecting the near and far mains meant you were looking for trip time troubles but if you had an end feed system with a bulk main from the riser feeding both the near and far mains cut trip times considerably.
Sometimes what we intuitively think turns out to be wrong and I believe this happens a lot in our industry especially when it comes to dry pipe systems.
For example I have a horseshoe dry pipe system consisting of a 6" riser, 4" mains and 2" branch lines that looked something like this but bigger than I depict here with a capacity of just under 900 gallons.
As you can see I left myself out "out" I could have cut the system in half adding another riser adjacent to the one I showed in which case the systems would have been < 750 gallons so trip time wouldn't matter.
It was one of those jobs where I wouldn't have staked my life in a guarantee of trip time but based on what I've seen over the years I thought it would be ok.
It was about this time I ran across this article by James Golinveaux who was with Tyco but is now with Viking.
If you haven't read it I would urge all designers to do so because I found it absolutely enlightening.
A Technical Analysis: Variables That Affect The Performance Of Dry Pipe Systems
James Golinveaux, Sr. Vice President,
Research & Development
Tyco Fire & Building Products
According to the Mr. Golinveaux's paper if I simply tied the two far branch lines together with a 1" piece of pipe, shown in green, I could expect a faster time to water to the inespectors test connection. I don't know about you but for me it ran counter intuitive to everything I ever thought I knew. Everyone knows grids and loops take longer, right?
But according to Mr. Golinveaux's paper by tying the two branch lines together I could expect a faster trip time due to compression of the air in the system instead of forcing more of it through the inspectors test.
The guys in the field thought their designer went totally nuts when I told them I wanted to do exactly that... try a trip before tying the two lines together and again after being careful to start at the same air pressure for each test.
Measuring the time by tying the two lines together I cut approximately 12 seconds off time to water through the inspectors test. Without tying them together we were right around 62 seconds for water to the inspectors test but after we tied the lines together we were right at 50 seconds.
I was amazed but if you take time to read the paper it does make sense.
Now what I am wondering is what would happen if we added 40 feet of 6" cross main at the end of the far main? We wouldn't add any lines so the inspectors test would remain where shown... we'd simply have a reservoir for trapped air.... would trip time go up or go down?
James Golinveaux will be a speaker at the
Florida Fire Sprinkler Association in Boca Raton later this month, I got to go to keep our Florida license. I'm going to try to corner him so we can talk for about eight hours. It's a tough part of the job someone has to do it. Anyone else from here going to be there?