MCFRS Engine Module 1: Exhaust Systems

Exhaust Systems

• Diesel engines since 2007 are equipped with "aftertreatment" systems, which include Diesel Exhaust Fluid (DEF) and Diesel Particulate Filter (DPF).
• DEF is a non-hazardous solution of 32.5% urea and 67.5% de-ionized water used to break down nitrogen oxide emissions.
• DEF is stored in a separate tank, typically with a blue filler cap, and should be refilled when it reaches half.
• Do not allow the DEF tank to reach empty, as the vehicle will automatically reduce power.
• DEF crystallizes when stored for prolonged periods and should not be used in that state.

Diesel Particulate Filter (DPF)

• DPF indicator illuminates when sufficient particulate has accumulated in the system, requiring regeneration.
• Regeneration occurs in two modes: automatically when the vehicle is at highway speeds for over 20 minutes or while parked.

Exhaust System

• The exhaust system is basic and consists of mufflers, exhaust pipes, tail pipes, and/or vertical stacks.
• A faulty exhaust system can affect motor performance and emit poisonous fumes into the crew area, causing serious illness.

Driveline

• The driveline consists of the transmission, front universal joint, driveshaft, rear universal joint, differential, and rear axle.
• The transmission is a system of gears that allows changes in the ratio of engine revolutions to wheel revolutions.

Automatic Traction Control

• Automatic traction control function aids tires in maintaining traction by monitoring wheel speeds and applying braking to a drive wheel that is spinning.
• In extreme situations, engine speed may also be decreased until traction is achieved.

Emergency Vehicle Pre-Response Preventive Inspections

• Emergency vehicles should be inspected prior to each shift and after an event or incident that may cause damage to the vehicle.
• The driver is responsible for confirming the vehicle is ready for use, and it is their responsibility to ensure mechanical safety.
• Preventive maintenance inspections identify problems and permit temporary repairs.
• Inspections, maintenance, and repairs must be recorded by the Department, including dates and descriptions of work performed.
• Inspections can be broken into nine core areas: prior maintenance records, vehicle overview, engine compartment check, interior cab check, vehicle walk around check, compartment and equipment check, undercarriage check, and more.

Braking and Stopping

• Effective braking is crucial for safe operation of an emergency vehicle, requiring timely and controlled application of brakes to maintain control.
• Prior to anti-lock braking systems (ABS), hydraulic brakes required pumping the brake pedal to avoid wheel lock, while air brakes required steady pressure to slow down without locking wheels.
• With ABS, do not pump the brake pedal, as it confuses the monitoring system; instead, apply steady pressure to signal the system to slow down.
• Even with ABS, vehicles can skid; if wheels lock, release the brake pedal and steer with the skid, then reapply the brakes to establish traction.
• In high-probability braking areas, "cover" the brake by hovering the foot over the pedal without applying pressure to reduce reaction time.

Safe Braking Techniques

• Allow enough space around the vehicle to identify the need to brake and apply brakes in a controlled manner.
• In heavy apparatus, expand the look-ahead distance to slow down using natural friction of the engine and compression.
• In curves, coast at speed to maintain traction and avoid accelerating, which can cause loss of control.

Exiting Curves

• Maintain speed and position on the inner surface of the curve.
• Gently accelerate out of the curve after the apex is reached and the vehicle is on a straight path.

High-Speed Braking

• Stopping at higher speeds requires more stopping distance and is harder on braking systems.
• Braking creates friction, which can cause overheating and reduce braking effectiveness.
• Reduce stress on brake systems by engaging auxiliary braking systems and downshifting the transmission.
• Drum brakes fade more quickly than disc brakes due to differences in heat dissipation capability.

Handling Unusual and Dangerous Driving Situations

• Emergency vehicle operators must adjust driving techniques for adverse conditions, including traction implications, environmental hazards, and vision implications.

Air Brake Systems

• A warning signal must come on before air pressure in the air tanks falls below 60 psi.
• The brake light switch warns drivers behind the vehicle when the brakes are applied.
• Spring brakes are used to meet emergency brake and parking brake requirements.
• Parking brake controls are typically operated using a diamond-shaped, yellow, pull-push control knob.

Parking Brake Controls

• Avoid pushing the brake pedal down when the spring brakes are on to prevent damage.
• Apparatus equipped with air brakes use driveline brakes or spring-activated brakes as parking brakes.
• Dual air brake systems are used for safety reasons in most new vehicles.

Braking Systems

• A vehicle's braking system converts inputs from the brake pedal or parking brake controls to the friction devices (brakes) located at each vehicle wheel.

Types of Braking Systems

• Hydraulic systems use liquid to create forces to engage friction devices.
• Pneumatic (air) systems use compressed air to make brakes work.

Drum Brakes

• Have drums located on each end of the vehicle's axles.
• Wheels are bolted to the drums and the braking mechanism is inside the drum.
• Brake shoes and linings are pushed against the inside of the drum to slow the vehicle.

Disc Brakes

• Comprised of a rotor and a caliper that squeeze the brake pads to stop or slow the vehicle.
• Rotor is the disc and is attached to the wheel axle.
• Caliper squeezes brake pads against the rotor to slow or stop the vehicle.

Pneumatic (Air) Brake Systems

• Most commonly used in fire service apparatus and commercial motor vehicles.
• Air brake system has three functions: service brake, parking brake, and emergency brake systems.

Components of Air Brake System

• Air Compressor: pumps air into air storage tanks, receives power from vehicle motor.
• Air Compressor Governor: automatically engages and disengages compressor to maintain preset levels in air storage tanks.
• Air Storage Tank: holds compressed air, number and size depend on vehicle size and auxiliary functions.

Issues with Air Brake Systems

• Water vapor in compressed air can lead to condensation and pools of water in air tanks.
• Moisture can lead to blockages, malfunctions, corrosion, or reduce capacity in storage tanks.

Types of Foundation Brake Systems

• S-cam Brakes: air pressure pushes rod out, moving slack adjuster, twisting brake camshaft, forcing brake shoes against brake drum.
• Wedge Brakes: brake chamber push rod pushes wedge directly between brake shoes, shoving them apart and against brake drum.
• Disc Brakes: air pressure acts on brake chamber and slack adjuster, turning power screw, clamping disc or rotor between brake lining pads of a caliper.

Other Components

• Supply Pressure Gauge(s): shows pressure in air tank(s).
• Low Air Pressure Warning: required on all vehicles with air brakes, signals low pressure.