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To determine which sprinklers in the building become the most remote area, a calculation is used. The number of sprinklers per branch line is equal to 1.2 times the square root of the area of operation, divided by the distance between sprinklers. So, in the preceding example, the number of sprinklers on the branch line is determined by the following calculation:
1.2 √A / S, where A is the area of application, and S is the spacing of sprinklers on the branch line.
In this example, (1.2 x √3000) / 10 = 6.57 sprinklers, rounded up to seven (7) sprinklers per branch line.
(3,000 is the area of operation; 10 is the distance between sprinklers on the branch line)
As there are 24 sprinklers in the remote area, calculations will include three (3) branch lines with seven (7) sprinklers, and three (3) sprinklers on the fourth branch line, beginning at the most remote part of the system. The last three (3) sprinklers in this case are the ones that are closest to the supply, as they will have to be supplied with the largest flow and pressure on that branch line.
This may not seem to make sense, as the seemingly most remote sprinklers on a branch line would be at the end of the pipe, where the pipe is smallest. However, that does not represent the highest flow that the system piping has to carry, as to reach the three (3) end sprinklers, the water supplying those has to pass through the first section of pipe. That means that the first section of piping has the highest hydraulic demand, thus they are the sprinklers to be calculated - they represent the worst case on the branch line.
© Hughes Associates,Inc. 2012