Fire Engine

Overview

A fire engine, or pumper, is a self-propelled apparatus that carries water, hose, ladders and crew to a fire and supplies pressurized water to attack lines. This unit is a midship pumper built on a custom cab-forward chassis: a centrifugal fire pump mounted amidships draws from an onboard tank or a hydrant and boosts it to the pressures handlines and master streams require. Unlike a ladder truck, the pumper's primary role is delivering water and foam, though it carries ground ladders and rescue tools as well.

Everything rides on the Truck Chassis, a heavy frame with a diesel powertrain, air brakes and dual rear wheels. The Crew Cab seats the crew with SCBA-mount seats. At the heart of the apparatus is the Centrifugal Fire Pump, a two-stage centrifugal pump driven through a split-shaft PTO. It draws from the Water & Foam System system, a 750-gallon booster tank with a foam cell and proportioner. The operator works the Pump Operator Panel, reading pressure gauges and setting discharge valves. The Apparatus Body holds hose beds, ground ladders and tool compartments, and the Warning & Deluge System system carries warning lights, the siren and a roof-mounted deck gun.

How it works

On arrival the driver sets the parking brake and engages the split-shaft PTO, which disconnects the driveline and routes engine torque to the pump shaft. The centrifugal impellers accelerate water outward, converting velocity to pressure in the volute; the two stages can run in series for high pressure or parallel for high volume. A priming pump first evacuates air so the pump can draft from a static source through the suction intake. The pressure governor holds a steady discharge pressure as lines are opened and closed by modulating engine throttle. Foam concentrate is metered into the discharge stream by the proportioner to produce a film that suppresses flammable-liquid fires. The pump panel gives the operator continuous control of every discharge while the booster tank or a hydrant supply keeps the pump fed.