There may also be special requirements specified by insurance underwriters or local authorities having jurisdiction e.g. restrictions on allowable maximum velocity. The model must precisely define all the nodes and pipes to be included in the hydraulic calculation. Node numbers describe specific points throughout the piping system to be calculated and carry information on elevations, sprinkler K-Factors and inside hose stream. Pipe numbers describe beginning and ending nodes, pipe diameters, pipe lengths, fittings, equivalent lengths and C-Factors. The beginning and ending nodes may define trees, loops, grids, compound grids and hybrid piping systems.
Density multiplied by area per sprinkler gives the flow required at the most remote sprinkler.
Use this value along with the sprinkler K-Factor to check the minimum starting pressure, which should exceed 7 psi. Select the next point upstream, calculate the pressure due to elevation and friction loss and add this to the minimum starting pressure at the most remote sprinkler. Extend this process to each and every node all the way back to the source node. If there are loops and grids along the way, route the flow through all the pipe segments in accordance with the principles of hydraulics and fluid mechanics. Add fixed pressure devices such as detector checks and valves to derive the total sprinkler pressure and flow at the source node.