How does foam fire truck's fire extinguishing system work-fire-trucks.com

How does foam fire truck's fire extinguishing system work

» The Underlying Logic of Foam Fire Extinguishing

★. Why can't water extinguish oil fires?

• Density difference: Water is heavier than oil and sinks directly to the bottom, never touching the flame.

• Boiling over: The water at the bottom vaporizes instantly upon contact with high temperatures, expanding thousands of times in volume, splattering the oil layer.

• Reignition: A small amount of water evaporating into steam only temporarily isolates the oil from oxygen; once the steam dissipates, the oil surface immediately reignites.

isuzu foam fire truck

★. How does foam work?

• Isolation: The foam covers the oil surface, forming a dense physical barrier that blocks the oxygen supply.

• Cooling: The foam contains a large amount of water; the evaporation of this water absorbs heat, continuously carrying away heat from the oil surface.

• Blocking: The foam layer prevents oil vapor from evaporating into the air, breaking the fuel-air mixing chain.

» Main components of fire extinguishing

1. Water and Liquid Supply – Two Independent Storage system

The foam fire truck has two separate tanks: a water tank and a foam liquid tank.

2. Fire pump

Fire pumps are the power heart of the entire fire extinguishing system, specifically designed for delivering water or foam solutions. Our fire trucks primarily use fire pumps from two well-known brands: Xiongzhen and Rongshen. Pressures include low, medium, and medium-low pressure; flow rates range from 20L/s to 180L/s; suction depth is 7m.

Among them, we commonly use the CB10/60 fire pump, with a flow rate of 60L/s and a rated pressure of 1.0MPa.

3. Fire monitor

Dual-purpose, capable of spraying water to extinguish solid fires and foam to extinguish oil fires; Our fire trucks primarily use Chengdu West fire monitors, which can spray water or foam liquid, and feature both spray pattern and direct current functions; they have long range, concentrated jet, high foaming ratio, and large protection area; they are flexible and convenient to operate, and the monitor body can rotate horizontally and vertically.

Among them, we commonly use the PL8/48 fire monitor, with a flow rate of 48L/s and a rated pressure of 0.8MPa; the range is ≥70m for water and ≥60m for foam.

PL8/48 fire monitor

4. Water guns and foam guns

Water or foam is delivered through pipes and fire hoses to the end fire guns/foam guns for fire extinguishing.

water/foam guns

5. Fixed foam proportioner vs. fully automatic foam proportioner

Comparison Dimensions	Fixed Proportioning (Circulating Pump Type, Negative-Pressure)	Variable- Proportioning (Circulating Pump Type, Negative-Pressure)
Mixing ratio	6%（example：PH64-RS）	1%～10%，step 0.5%
Work pressure range	0.6～1.4MPa	0.6～2.5MPa
Flow range	16～64L/s	TAF-PH120，120L/s；TAF-PH240，240L/s
Proportioning accuracy	Highly affected by water pressure and pipeline resistance, resulting in significant errors.	Real-time dynamic correction ensures high proportioning accuracy and minimal error.
Applicable Scenarios	Suitable for large and medium-sized fire trucks with constant flow rate and stable pressure	Suitable for scenarios with large flow rate variations and multiple operating condition changes
Maintenance complexity	Low, simple structure	Medium, requires calibration due to sensing elements
Cost	Low	High

Fixed foam proportioner

Fully automatic foam proportioner

6. Piping System

Taking the Isuzu 8+2 cubic meter foam fire truck as an example:

♦ Suction Pipe: One DN150 suction port is located at the rear of the pump house, equipped with a filter and

Pneumatic butterfly valve switch

♦ Injection Pipe: One DN65 injection port is located on each side.

♦ Discharge Pipe: One DN65 and one DN80 discharge port are located on each side.

♦ Fire control system: All operating buttons are labeled and accompanied by piping layout and operation/maintenance diagrams. The instrument panel is located in the upper left of the pump house and is equipped with a tachometer/vacuum gauge/pressure gauge/water level gauge/foam level gauge, as well as lighting/valve control switches.

Piping diagram for water tank and foam tank

» How does the fire extinguishing foam formed?

1. The foam mixture (water + foam concentrate) is still a liquid, with a flow rate similar to water. True foam requires a large amount of air to be incorporated into the mixture.

2. A key design feature of the foam cannon/gun nozzle is the air intake.

When the high-pressure mixture passes through the nozzle at high speed, a localized negative pressure is created, forcibly drawing air in through the air intake. The air and liquid flow collide and shear violently within the nozzle, instantly breaking down into billions of tiny bubbles, which accumulate to form white foam.

» Foam Fire truck fire extinguishing working principle

The foam fire truck has dual-mode operation functions of independent water discharge and foam discharge:

It can simply extract clean water, pressurize it through a water pump, and spray clean water through hoses and fire cannons to extinguish conventional solid fires;

Foam fire truck water testing

The foam proportional mixing system can also be started to fuse clean water and foam liquid according to the standard ratio to form a foam mixture. After being pressurized by the water pump, the fire water is brought to the foam gun or vehicle-mounted fire monitor for spraying. The mixture and air are fully integrated to form air foam. Foam can quickly cover the surface of flammable liquids, isolate air, cool down and retard flames, inhibit oil and gas volatilization, and prevent re-ignition. It specializes in flammable liquid fires such as gas stations, chemical industries, and oil depots.

Foam fire truck foam testing