Exam Questions for Categories C and CE
KETBILIETAI® users report that many candidates do not pass the Regitra category C or CE exam on their first attempt. Even after attending lessons and studying the theory, questions about pneumatic braking systems, hydraulics, mechanics, spring-loaded valves and air reservoirs can prove difficult. This page therefore introduces some of the theory needed when preparing for category C and CE exams.
In the KETBILIETAI® tests, you will find the following questions on the following topics:
WHAT SHOULD YOU DO IF THE WHEEL BRAKE LOCKS DUE TO A LEAK IN THE REAR WHEEL CYLINDER (ENERGY ACCUMULATOR)?
EXCESS AIR IS REMOVED WHEN THE SAFETY VALVE IN THE BRAKE SYSTEM RECEIVER IS TRIGGERED:
WHY MAY THE AIR PRESSURE IN THE PNEUMATIC BRAKE SYSTEM NOT RISE TO THE NORMAL LEVEL?
WHAT CAUSES A LONGER THAN NORMAL FILLING TIME FOR THE BRAKE SYSTEM?
HOW CAN SEVERAL BROKEN SUSPENSION SPRINGS AFFECT VEHICLE SAFETY?
WHAT PRECAUTIONS SHOULD BE TAKEN WHEN OPERATING A VEHICLE WITH AN AIR-BRAKE SYSTEM IN WINTER?
HOW DOES A BROKEN SUSPENSION SPRING AFFECT VEHICLE STABILITY?
WHAT ARE AIR SUSPENSIONS MADE OF?
And many others.
More information about air-brake systems is available here: Download the PDF
Below is an additional short overview of theory for categories C and CE:
Electropneumatic brakes rely on the force of compressed air, which provides hundreds of times more effective braking than can be achieved mechanically.
Brakes with a pneumatic actuator are actuated by compressed gas, such as air.
Structure of the pneumatic brake system
The pneumatic brake system consists of wheel mechanisms and the pneumatic drive itself. In modern cars, a multi-circuit drive is used (a circuit is a part independent of other lines). It is also called "separate". A "continuous" (single circuit) drive was used in old cars.
The pneumatic brake drive consists of 4 autonomous brake systems: working, reserve, parking brake and auxiliary. Such mechanisms are installed on all four wheels. Each part of the air brake actuator has a different function.
The service brake is used in a moving vehicle. It stops the vehicle or slows it down when necessary. The drive of the service brake is pneumatic, with two circuits. It forces the brakes of the front axle and the rear axle to work separately. The drive is controlled by a pedal connected to the brake valve. Service brake actuators are brake chambers near the wheels.
The backup brake is used when the vehicle needs to be slowed down evenly. Also when the service brake is broken. The backup brake is controlled by the brake valve, which activates the parking brake system.
The parking brake is used when the vehicle is stationary. It is equipped with a spare brake. The parking brake is activated using a knob located on the handbrake valve.
The auxiliary brake is designed to reduce the speed of the vehicle on slopes. It also reduces the load on the brake mechanisms in the wheels, at the same time extending their service life. The auxiliary brake works by using the compression of the car's engine: this is the process of closing the exhaust pipe and, at the same time, cutting off the fuel supply.
These listed brake systems have the same structure, but work independently of each other. This ensures that a massive vehicle such as a trolleybus, bus or truck will be stopped effectively.
By the way, in addition to the listed brake systems, some vehicles are also equipped with an emergency brake release system. It allows the vehicle to move when it is braked automatically, for example due to a large air leak. The energy accumulator mechanically creates a tension force. The emergency brake release system works by releasing the battery springs if they are activated automatically.
The back-up brake release system is useful when a stationary vehicle needs to be removed from a dangerous area in an emergency. For example, from a railway crossing.
The back-up brake release system can work not only pneumatically, but also mechanically. It is controlled by an emergency tap that supplies compressed air to the spring brake actuator. It mechanically unscrews the bolt from the spring brake actuator and thus releases the spring. But, this process takes quite a long time.
The pneumatic brake actuator consists of a common part of the compressed air supply and separate, mutually independent compressed air lines (circuits). The general part of the compressed air supply consists of a compressor, a pressure regulator, a condensate freeze fuse, a double safety valve, a triple safety valve and a condensate cylinder.
Safety valves direct compressed air to separate circuits. The most common are five circuits. Each circuit operates independently of the other circuit, even in the event of a fault. The picture shows the actuator of a "separate" air brake system, showing the compressor, pressure regulator, anti-freeze, double safety, valve, triple safety valve, air cylinder for moisture condensation, condensate drain valve, first circuit air cylinder, second circuit air cylinder, third circuit air cylinder, pressure drop sensors, check valves, auxiliary brake valve, tap to release energy accumulators (parking brakes), fuel cut-off control cylinder, exhaust pipe closing control cylinder, two-section brake valve, pressure gauge, brake chambers, pressure relief valve, parking and reserve brake valve, accelerator valve, brake chambers with spring energy accumulators, "two-line" bypass valve, trailer dual-pipe brake system control valve, "single" safety valve, control valve of trailer "one-pipe" braking system, disconnecting taps, connecting heads, "stop" signal sensor, brake force regulator, air intake valve, parking brake activation sensor and trailer brake electromagnetic valve activation sensor.
The purpose and structure of the five circuits
The pneumatic brake actuator, together with the general part of the compressed air supply, consists of compressed air lines - contours.
First circuit
Controls front axle service brakes and trailer brakes. It consists of a part of a triple safety valve, an air cylinder with a condensate discharge tap and a pressure drop sensor (a measuring device for measuring and transmitting physical quantities). Also includes two-point gauge part, two-section brake valve lower part, control valve, pressure relief valve, two brake chambers and trailer dual-pipe brake system valve, trailer single-pipe brake system control valve, isolating valve and connecting heads, brake mechanism in front wheels and pipes and hoses between these parts.
Second circuit
Controls the service brakes of the intermediate and rear axles and the trailer. It consists of a part of a triple safety valve, two air cylinders with a condensate drain tap and a pressure drop sensor in the cylinders, a part of a two-point pressure gauge, an upper part of a two-section brake valve, a brake force regulator, four brake chambers, a control valve for the trailer's two-pipe brake system, and other parts in the first circuit.
Third circuit
Controls the parking (spare) brake of the car and the trailer brakes. It consists of a part of a double safety valve, air cylinders with a condensate drain tap and a pressure drop sensor in the cylinders, a manual brake valve, an accelerating valve, a part of a two-line valve, four chambers with spring energy accumulators, a control valve for the trailer's two-pipe brake system, a single safety valve, a control valve for the trailer's single-pipe brake system, a shut-off valve, a connecting head (there are two types of heads: one type of head is for trailers with a dual pipe brake system and another type of head is for trailers with a single pipe brake system), a pneumatic sensor (for the stop signal), tubes and hoses connecting these parts. Please note that the sensor in the circuit is installed in such a way that it activates the "stop" signal when the vehicle is stopped with the service brake and the handbrake, as well as when one of the circuits fails.
Fourth circuit
Controls auxiliary brakes and supplies air to other mechanisms (window wipers, pneumatic horn, control of transmission units). It consists of part of double safety valve, pneumatic control valve, exhaust pipe flap control cylinder, fuel cut-off control cylinder. Compressed air for this circuit is supplied from a condensing cylinder.
Fifth circuit
Releases the parking or emergency brake. This circuit does not have its own balloon and executive parts. It consists of a part of a triple safety valve, a pneumatic control valve and a part of a "dual line" valve.
Control system
In addition to brakes, vehicles are also equipped with electrical devices that monitor the operation of the pneumatic brake system. A car with a trailer is equipped with brake system elements that control the trailer's brake system. The control system can consist of two parts: electrical devices (in the instrument panel) and control inputs, to which the connected control devices determine the state of the pneumatic brake actuator.
The information is prepared based on motofocus.lt
