AIR BRAKES AND THE DRIVER-OPERATOR
BY TERRY ECKERT
Do you know what stops that 40,000-pound fire engine?
The driver-operator has a tremendous responsibility every time he steps behind the wheel of the fire apparatus and also when performing daily, weekly, and monthly routine checks. An extensive list of dos and don`ts applies to the driver-operator. The list includes, among many other things, having a working knowledge of engine and pump operations, pump hydraulics, the rules of the road, safe driving practices, and safe stopping distances.
Current Fire Apparatus Engineer (FAE) training is striving to prioritize safe driving techniques. One of the things a driver-operator learns during FAE training is about air brake apply time and the resulting increased following and stopping distances necessitated by the air brake system. But the driver-operator should also know how the air brake system works to more fully understand the logic behind the air brake apply time and the required following and stopping distances. Unfortunately, most department FAE training programs omit this essential and necessary part of a driver-operator`s training program.
LAG TIME
Lag time is the time it takes the brakes to take effect after the brake pedal has been applied. Understanding why the lag time exists will help the driver-operator better appreciate the special techniques required to stop a heavy vehicle with air brakes and deal with the everyday driving decisions, as well as most likely change his driving habits.
Lag time is nonexistent in the hydraulic system found in cars and light trucks. The advantage of a hydraulic system is that the fluid is always in the system and is relatively noncompressible. The moment the brake pedal is depressed, all the brakes work instantly.
The disadvantage of an air-brake system is that it works by using compressed air. Air brakes have a normal operating pressure of approximately 110 psi. When the foot brake (service brake) is applied, air moves through a series of valves, air tanks, hoses, and relays until the air fills voids in the empty lines and empty brake chambers before the brake applies. The air pressure in the system will actually drop as it is moved from one location to another. To increase the pressure, a large diaphragm (approximately 36 square inches) is used in the brake chamber located at each wheel. Add all these factors together for every brake assembly, and you can understand why it takes so long for the air brakes to apply. If the brakes are out of adjustment, more air is needed. For a system in good operating condition with properly adjusted brakes, it will take from one-half to one second to apply.
The heavier and larger the truck, the bigger the system and the longer the brake lag. This brake lag at 55 mph can add 60 feet to your stopping distance. Taking into consideration all the other factors taught in high school driver education classes, such as perception, reaction, and actual stopping distance (and also assuming good brakes, tires, road conditions, and a vehicle that is not overloaded), the experts say that it takes more than 300 feet to stop at 55 mph. Think about it: Are you really looking ahead the length of a football field? Are there factors that are not under your control that could make the car in front of you stop quickly? Understanding how and why brake lag exists makes believing it a lot easier. Make sure all driver-operators believe in brake lag. Incorporate it into your driver-operator program.
THE AIR BRAKE SYSTEM
Most states permit a driver-operator the luxury of operating fire apparatus (only while on duty) with a non-CDL (commercial driver`s license). Most states` reasoning behind this “luxury” is that the driver-operators are selected by the department that employs them, they exhibit professionalism, and the fire service training and testing are far superior to what is afforded to most over-the-road commercial CDL operators.
In case you do not know, operators holding a CDL are required by the state to have a basic knowledge of an air brake system and take a separate test solely dedicated to air brake systems.
If you are a driver-operator, ask yourself these two very simple, yet vital, questions: (1) Can I recognize a problem in the air brake system before brake failure occurs? and (2) If brake failure does occur, do I know how to safely stop the apparatus? If you do not know the correct answers to both these questions, the time has come to incorporate air brake systems into your department`s FAE training program.
Some Basic Questions
Whenever I teach a class on air brake systems, I like to start by asking some basic questions. I am constantly amazed at the diversity of answers I receive. The following five questions are a sampling (the correct answers are given below).
1. Most air brake systems have two dashboard air gauges. What do the two air gauges indicate?
2. For what two reasons does the driver-operator need to know how much pressure is in each system?
3. On vehicles with multiair tanks, which tank is known as the “wet tank”?
4. How does the parking brake work?
5. What is the emergency brake?
The Answers
1. The first gauge identifies the air pressure in the primary system (marked “primary” or “rear brakes” or displays a red needle). The air pressure in the primary system controls the rear brakes. With the heavy loads fire apparatus carry on the rear axles, the rear brakes can perform up to 80 percent of the braking.
The second gauge identifies the secondary system (marked “secondary” or “front” or displays a white or green needle). This gauge indicates the air pressure that controls the front (steering) brakes. Usually, most air-operated accessories (such as the air horn) will also operate from this tank and be registered by this gauge.
2. Reason 1: By reading the gauges and knowing how much air is in each system, the driver-operator can estimate how much braking power the vehicle has.
Reason 2: During a failure in one or both brake systems, the driver-operator can make an informed decision as to whether he (a) needs to make an emergency stop, (b) can safely stop the vehicle without having to make an emergency stop, or (c) can safely and slowly return the vehicle to quarters.
3. This tank is also known as the “main tank.” It is the first tank to receive the hot compressed air from the compressor. As compressed air cools in the tank, water is condensed and stored in the main tank (wet tank). Since water is destructive to the air brake system, it is important that the water be expelled by proper operation of drains and air dryers. If excessive water or oil is found in the wet tank during the checks, this must be reported to maintenance; it might indicate a failure of the compressor or air dryer. The other tanks, one or more of which operate the primary system and one which operates the secondary system, should always be dry. If they are not dry, there is a problem. All tanks should always be checked daily for water.
4. Parking brakes are installed on the rear axle(s) and use the rear air brake chambers. Springs apply the rear brakes and therefore are applied without the use of air pressure. To release the parking brake, air is sent to the chambers by the diamond-shaped parking brake knob and compresses the springs, which release the parking brakes. Experience and common sense tell you that if you lose air pressure, the parking brake will apply automatically.
5. NO, it is not the parking brake! It is a system all its own. In case of total loss of pressure in either the primary or secondary tanks, the emergency brake system will use existing air so that when the brakes are applied, a controlled combination of parking and service brakes will activate so that the rear-controlled braking occurs under any circumstance. The existence of this braking system allows the release of the parking brake when air is at a minimum of 30 to 50 pounds in either the primary or secondary systems. This system should be checked by qualified technicians during every preventive maintenance. This is critical on apparatus that often operates with minimum air pressure, such as when leaving the fire station before the air pressure is properly built up.
As you can see, it is important for departments to create and maintain programs for fire apparatus air brakes. The driver-operator must know how to stop the vehicle. Driver-operators should be able to identify most problems from proper daily maintenance and inspection and to stop the vehicle safely or return it to quarters should the brakes fail. With the number of accidents and the liability involved, complete driver-operator training is essential.
CHECKLIST
It is essential that brakes be checked daily and that the results be recorded. Remember: If it is not written down, it did not happen. Liability must always be considered when developing a brake training and checkout program. Consider this proposition: If the state CDL program requires daily brake checks for over-the-road truck operators, what excuse will the fire department give to the judge for not holding its driver-operators to the same standards?
Use a checklist custom-tailored to your department`s driving habits, location, and terrain. Find out what your state`s requirements for over-the-road drivers are. Pick up a copy of your state`s CDL Drivers Guide and follow at least the same daily checks. A partial sampling of some of the items that should be included on your checklist is given on page 23.
This partial list should help you to develop a brake checklist. The use of the fire apparatus will vary from town to town and state to state. Because of all these types of service variations, I cannot recommend any timetable for these checks, except where noted. The individual department would be better equipped to develop its own timetable. It is imperative that the maintenance technicians work with their individual departments to develop this vital checklist.
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Brakes are sometimes the most abused component on the fire apparatus, and brake system failure probably poses the greatest hazard for firefighters and the public. Driver education followed by a thorough daily brake checkout is a good starting point for preventing such a failure. Also, a qualified truck technician should maintain, repair, and replace the brake system. Safety is the selling point of this program: If it prevents one accident or even a “close call,” it is well worth the time, effort, and money.
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(Left) The driver operator must constantly be aware of the engine`s air brake apply time and, at the same time, consider following and stopping distances. (Center) The driver often overlooks the weight difference between an engine and an aerial ladder truck until it is too late. (Right) Every year a large number of firefighters are killed and seriously injured in apparatus accidents involving tankers. The driver-operator must realize that the tanker`s weight will change throughout a shuttle operation and that when full the tanker may even be “top heavy.”
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Most air brake systems have two dashboard air gauges. (Top) The primary system often is marked “primary,” “rear brakes,” or with a red needle. (Bottom) The secondary system is marked “secondary,” “front,” or with a white or green needle.
AIR BRAKE CHECKLIST
q Test low air pressure warning light and buzzer.
This should engage if either tank falls below approximately 50 pounds.
q Test air compressor cut-in and cut-out pressure.
Most compressors start at about 100 psi and turn off at approximately 125 psi. (Check the manufacturer`s specifications, and list them on your checkout list.)
q Check accessory cut-off.
Items such as air horns shut off at 90 psi.
q Test parking brake.
Check for drag by applying when pulling away from a stop in Drive. It should hold at least a 20 percent grade forward or backward. Failure most likely will be to due to out-of-adjustment or broken chamber spring(s).
q Drain air tanks.
Manually drain all air tanks daily. Report any excessive water or oil found to your maintenance department. This could indicate a problem with the dryer or the compressor. This check must be done daily or after every run.
q Check compressor belt (if so equipped).
Check the condition and tightness.
q Check slack adjusters.
Check on level ground with wheel chocked and parking brake off. Apply service brake with a least 100 psi in system, push rod–it should move no more than 112 inches. (Check the manufacturer`s recommendations.)
q Check that parking brake comes on automatically at low pressure.
The parking brake should apply at 20 to 30 psi. (Check manufacturer`s specifications.)
q Check rate of air pressure buildup.
Most systems will take a few minutes to build up from 0 psi. Make sure that the primary system starts to build up first. Buildup time from 90 to 125 psi should take less than a minute. (Check manufacturer`s specifications and NFPA standard for buildup times.)
q Check air leakage rate.
Check with the engine off and the parking brake on. Immediately report any unusual air leakage. (Individual departments may want to incorporate stricter requirements for leakage rates than the manufacturer specifies or National Fire Protection Association standards allow.)
q Conduct a visible check.
Visibly check the tanks, hoses, and all brake-mounting equipment. With some vehicles, brake linings and drums (or rotors) can be visibly checked.
q Check foot pedal.
Look for dirt and rust at the pivot pin; check for ease of movement.
q Check the air compressor.
Make sure it is mounted securely and has no missing bolts.
q Clean air filter or intake system.
This is the most forgotten maintenance item. It may be done by a maintenance technician during PM (preventive maintenance).
q Check emergency brake system.
This also may be done by a maintenance technician during PM.
TERRY ECKERT, a 15-year veteran of the fire service, is a firefighter and head of apparatus maintenance in the Darien-Woodridge (IL) Fire District and the chief engineer of the Westmont (IL) Fire Department. He has 25 years of experience as a vehicle technician. He is an ASE-certified master automobile technician and master heavy truck technician and an EVT Level 3 master technician. He also has ASE certification in advanced level engine performance. Eckert is a member of numerous professional associations, including the National Association of Emergency Vehicle Technicians (NAEVT) and the Illinois Fire Apparatus Mechanics Association. He is a member of the EVT Certification Commission, where he serves on the Validation Committee and had chaired the E-3 section, and the NFPA Technical Committee on Emergency Vehicle Technician Professional Qualifications. He was the 1997 recipient of the NAEVT Certificate of Achievement Award.
