FireOps CalcWye PDP = Main Line FL + Highest Branch Requirement + Appliance Loss
Branch Requirement = Branch FL + Nozzle Pressure ± Elevation
Step-by-step process
Calculate total flow in the main lineAdd the flow from each branch line.
Calculate main-line friction lossUse the combined GPM through the supply line feeding the wye.
Calculate each branch requirementEach branch gets its own hose length, flow, and nozzle pressure.
Pick the highest branchThe pump must satisfy the branch with the greatest pressure requirement.
Add appliance lossAdd wye/manifold loss according to department practice.
Worked example
Main supply200 ft of 2½ inch
Branch A150 ft 1¾ inch, 150 GPM fog
Branch B200 ft 1¾ inch, 185 GPM fog
UseMain FL + highest branch + wye loss
ResultUse highest-loss branch path
Do not simply add both branch friction losses together. The pump pressure follows the highest required path, while the main line carries the combined flow.
Common mistakes to avoid
- Using a default nozzle pressure that does not match the actual nozzle.
- Forgetting extra hose, elevation, or appliance loss.
- Using textbook coefficients when your department has known hose data.
- Treating a training estimate as a replacement for department SOPs or instructor direction.
How FireOps Calc helps
FireOps Calc is built to make this process faster on a phone. Open the web calculator, enter your hose, nozzle, flow, elevation, and appliance values, then review the math breakdown instead of only seeing a final number.
FAQ
Why do I use the highest branch instead of adding branches?
Parallel branches each receive pressure from the same split point. The pump must supply enough pressure for the branch with the greatest requirement.
Does total GPM still matter?
Yes. Total GPM matters in the main supply hose before the wye.