FireOps CalcRelay layout terms
For FireOps Calc, number of engines should mean the total pumpers in the relay, including the source engine, any relay engines, and the receiving or attack engine.
| Engines | Layout |
|---|---|
| 2 | Engine 1 → Engine 2 |
| 3 | Engine 1 → Engine 2 → Engine 3 |
| 4 | Engine 1 → Engine 2 → Engine 3 → Engine 4 |
Distance between engines
In basic equal-spacing mode:
Distance between engines = total relay distance ÷ hose sections
Example: 2,000 ft total relay distance with 3 engines gives 2 hose sections, so engines are spaced about 1,000 ft apart.
Relay PDP formula
Each relay section should calculate its own pressure:
The target intake pressure is commonly set around 20 PSI for training examples, but the user should be able to edit it based on department guidance and the receiving engine’s needs.
Worked example
| Input | Value |
|---|---|
| Total Flow | 1000 GPM |
| Total Distance | 2000 ft |
| Number of Engines | 3 |
| Sections | 2 |
| Distance Between Engines | 1000 ft |
| Display | Engine 1 → Engine 2, then Engine 2 → Engine 3 |
Advanced mode should also allow manual unequal distances, such as 800 ft for the first section and 1,200 ft for the second section.
FAQ
How do you calculate distance between relay engines?
In basic mode, subtract one from the number of engines to get hose sections, then divide total distance by that number.
Why show each engine-to-engine segment?
Each segment may have different hose length, elevation, or supply line count, so each relay engine may need a different PDP.
Should relay pumping use nozzle GPM?
No. Relay and water supply calculations should use a user-entered total flow GPM, not a zero-GPM supply nozzle.
Related FireOps Calc pages
Run the calculation in FireOps Calc.
Use the website calculator, install the app, or keep reading the training pages to build stronger pump operator habits.