Evolution 12 — Multi-Line Capacity Management

Overview

The capstone evolution. Three discharge lines operate simultaneously from a single hydrant — an interior attack line, a backup/exposure line, and a deck gun master stream. Total flow demand pushes the pump and water supply to their limits. This evolution tests every skill learned in the previous eleven evolutions: pressure balancing, intake monitoring, capacity management, and throttle discipline under stress. At 150 + 250 + 500 GPM, total demand is 900 GPM — 60% of a 1,500 GPM pump's rated capacity, but potentially exceeding the hydrant's available flow. The operator must manage three different target pressures simultaneously while watching intake for signs of supply collapse. Every line affects every other line. Opening the third line causes pressure changes on the first two. Closing one line causes pressure spikes on the others. This is the evolution where everything comes together.

Training Objective

Simultaneously supply three discharge lines at their correct pressures while managing total flow demand near the pump's rated capacity and maintaining safe intake pressure. The operator must demonstrate sequential line opening, real-time pressure balancing, and priority-based flow management if supply becomes marginal.

Skills Practiced

• Multi-line pressure management under maximum demand
• Pump capacity awareness and rated flow limits
• Priority-based flow allocation — knowing which line to sacrifice
• Cavitation prevention at high flow rates
• Sequential line opening under load to minimise pressure transients
• Real-time pressure balancing across three independent lines
• Intake monitoring under near-capacity demand
• Throttle discipline at high RPM with multiple competing demands
• Communication with multiple crews about pressure status

Setup

Single hydrant supply feeding three discharge lines: a 1¾" interior attack line (150 GPM), a 2½" backup/exposure line (250 GPM), and a deck gun master stream (500 GPM). Total demand of 900 GPM approaches the hydrant's available flow. Each line has a different target pressure based on its hose size, length, nozzle type, and flow rate.

Scenario

A large commercial structure fire requiring simultaneous interior attack, exposure protection, and defensive master stream operations. The IC has ordered all three lines flowing. The pump operator must keep all three lines at target pressure without exceeding the water supply or pump capacity. If the hydrant cannot sustain 900 GPM, the operator must decide which line to reduce — and communicate that decision to command.

What to Expect

This is the most demanding evolution in the curriculum. Every line affects every other line. Opening the third line will cause pressure changes on the first two that must be corrected within seconds. The simulation scores pressure accuracy on all three lines independently, monitors intake pressure for supply collapse, and penalises unsafe conditions including cavitation, over-pressurisation, and extended periods outside tolerance. Expect to make constant small adjustments throughout the evolution.

Tips

• Plan your line opening sequence before starting — open from highest demand to lowest
• Know your total flow demand (900 GPM) and compare it to your hydrant's capacity before opening the third line
• If intake pressure drops below 20 PSI, reduce the lowest-priority line first — usually the exposure line
• This evolution requires constant attention to all gauges simultaneously — develop a scan pattern
• Stay calm — this is where training pays off. Panic leads to large throttle corrections that make everything worse
• Calculate PDP for all three lines before opening any valves — write them down if you need to
• When the third line opens, increase throttle immediately and then fine-tune — do not wait for pressures to settle on their own