Trailer brake control valve: operating principle, connection

The standard trailer brake control valve serves to control the semi-trailer brakes when a similar tractor system operates. In addition, he is responsible for the automatic activation of the brakes in the event of a critical drop in pressure in the main. The drive of this node is a combined type (one and two-wire). Consider the design features, device and connection of the device.

Short description

The trailer brake control valve consists of the following elements:

• Pair control valve and similar single element.
• Two disconnection cranes.
• A pair of connecting heads.

The valve is responsible for controlling the brakes of the semitrailer, directs the compressed air from the input source to the subsequent consumers working both synchronously and separately. To the two terminals, a command is given to increase the pressure in the pipeline, and a reverse effect acts on one analog, which affects the pressure drop when the air mixture is released by means of a hand lever.

Check Valve

The trailer brake control valve is equipped with a main valve, which consists of three sections, a large and small piston with springs. The middle piston element has an inlet valve that presses the spring against the seat.

The remaining parts of the part in question are:

• Diaphragm.
• Discharge opening.
• Stock.
• Adjusting screw.

In the disinhibited position, compressed air is constantly supplied to the output parts. It acts on the diaphragm and piston, keeps it together with the stem in the lower position. This is facilitated by the increased area of the diaphragm. At the top, the piston group is located in the extreme upper position, and the outlet valve is separated from the seat. The inlet analog is in the closed state under the influence of a spring. One of the pins connects the brake control line to the atmospheric outlet by means of unloading holes and a rod.

Valve operation during braking

The valve of the brake control valve of the KamAZ trailer at braking supplies compressed air from the device sections to the terminals. From the other outlet of the air tank, the compressed mixture enters the control terminal, and then goes to the main section. There, the air acts on the piston until it is balanced from below under the upper pressure. The upper piston operates under the force of air pressure and a spring. In this case, the average piston must also be balanced under the influence of identical factors. In principle, there is a general tracking effect.

When disinhibited, air in a compressed state is discharged through the atmospheric opening of the valve from the filled compartments. The pistons under the pressure of the spring and air mixture become in the upper position, and the rod with the piston moves downward. The valve opens from the landing socket and connects the internal and external input.

Suitable compressed air causes the rod with the piston to move separately, and the large and small piston element down. The subsequent work of the brakes takes place according to a similar principle.

When the spare or parking truck system is activated, the compressed air is supplied through the atmospheric port in the hand-operated return valve and exits outwards. The degree of pressure above the diaphragm decreases, decreasing the force of action on the working elements. The saddle rests against the valve, separating the output terminal with the atmosphere. Then the valve opens, communicating the output and the main line.

Features

In the trailer brake control crane, the main pressure is pumped until the force acting on the piston from below is equalized with the action applied to the diaphragm. In this case, the servicing of the valve is ensured.

When an air compressed mixture approaches simultaneously to the working terminals, and the pressure in the compartment connected to the pipeline, and the pressure exceeds the analogous value in the control terminal (20-100 kPa), the brakes are advanced. The value of the required pressure index is adjusted by means of an adjusting screw, by twisting or unscrewing it.

Single safety valve

This element serves to maintain pressure in the air tank of the tractor in the event of a critical reduction of this index in the supply line of the semitrailer. In addition, it prevents the leakage of compressed air from the system when the pressure in the vehicle's drive drops abruptly, which prevents unauthorized braking of the trailing device.

A single valve is adjusted to the air bypass when the outlet pressure reaches 550 Pa. The compressed mixture enters through the outlet into the working niche under the diaphragm, then into the cavity in front of the valve. From there it goes to the main road exit. The value of the required pressure index is made by an adjusting screw.

Isolation crane

This part participates in the operation of the trailer brake control valve as follows:

• It, if necessary, overlaps the pneumatic main, the aggregating tractor with a towing device.
• If you place the handle of the tool along the crane's axis, the pusher with the stem will be in the lower position and the valve will open. Air in a compressed state through it and the corresponding output is sent from the car to the semitrailer.
• When the handle is placed across the frame, the rod and diaphragm move upward under the influence of air and spring pressure. The valve blocks the terminals by sitting in the saddle. The air mixture comes from the connecting system to the atmosphere, which makes it possible to disconnect the connecting heads.

Below is a schematic representation of the crane, as well as the main designations and components.

• A - the device is not active;
• B - open crane position;
• 1 - exit to the control valve of the air tank of the tractor through a single safety valve;
• II - Trunking the braking system of the trailer;
• III - atmospheric conclusion;
• 1 - the spring mechanism;
• 2 - the valve;
• 3-diaphragm with stem;
• 4 - a returnable spring;
• 5 - pusher with handle.

Connection head "Palm"

It is these parts of the KAMAZ trailer brake control valve that are also used in MAZ and Ural systems. Elements serve to combine the dual-circuit pneumatic drive of the truck's TC and semi-trailer. They are heads without valvular type, a rubber seal is used to seal the butt joints. The design of the assembly also includes fixators, which are responsible for retaining the parts in the engaged state.

Single-wire system

Unlike the two-wire trailer brake control valve, this design consists of a control valve, an unlock analog and a connecting L-shaped head.

The brake control valve with a single-wire drive operates through a single trunk, used as a supply and control system. It should be noted that the valve functions to reduce pressure in the main line, with the possibility of bringing the indicator to the atmospheric parameter. When the pressure decreases, the braking rate of the trailer is increased. Other parts of the crane include: a pusher with a diaphragm, a piston of a step type, valves (inlet and outlet). They aggregate among themselves by means of a connecting rod. There is also a lower piston.

Work in the disinhibited state

In the inactive position, air in a compressed form comes from the cylinder of the parking brake system to the outlet, which is connected to the atmosphere by means of a control valve. Under the influence of a power spring, the diaphragm and the pusher are located in the lower position. The exhaust valve remains closed, and the inlet analog operates open, allowing air to flow to the terminal, which aggregates with the brake control line with a single-wire drive.

Synchronously compressed air is supplied to special cavities, the pressure in which remains equal. Given that the area of the stepped piston is larger, it moves up to the stop. When the pressure in the brake chamber of the trailer reaches 500-520 Pa, the lower piston goes down and blocks the intake valve. In the disinhibited state, the system automatically maintains a pressure level of 500 Pa, which is somewhat lower than the similar parameter in the pneumatic drive of the truck.

How does the system function during braking?

When the tractor brakes are activated, the compressed air from the dual-circuit valve comes to the valve of a single-wire MAZ trailer brake control valve. The mixture fills the plane under the diaphragm. After overcoming the force of the spring, the diaphragm is fed upward along with the pusher, the inlet valve closes, the outlet element opens. The air leaves the atmosphere, bypassing the special terminal, pusher and hole in the lid.

The stepped piston performs the follow-up action. If the pressure at the outlet and in the cavity decreases, the force of action on the piston from below decreases. In the upper part, this element is subjected to pressure from the corresponding cavity, identical to the force in the second compartment. The hub, in turn, perceives the force from the first cavity. As a result, due to the pressure difference, the piston moves downward, carrying the pusher, which closes the outlet window with its saddle. The subsequent increase in pressure causes a complete release of the air mixture from the main brake construction of the semitrailer. The pusher is in this case in the lowest position, the inlet window is blocked, the outlet element is open.

Variable mode

Connecting the brake control valve of the trailer implies normal operation of all components of the device. A single-wire version, when the brakes of the tractor is loose, interacts with the atmosphere through the provided valve opening of the two-wire drive. The pressure in the working cavity is reduced, and the diaphragm with the pusher moves to the starting position, blocking the exhaust valve and opening the inlet element. Air in a compressed state enters the output and the connecting system of the trailer, releasing it.

The L-shaped coupling head aggregates with the main line of a single-wire drive, automatically closing the truck's coupling system in case of spontaneous disconnection of the heads, which can happen when the trailer is uncoupled. The head is equipped with a valve, blocked by the action of the spring in the disconnected element, and opens in the connected head by means of a pin.

Wabco Trailer Brake Control Valve

It is these structures that are equipped with trailers, connected with the cars of the brand "MAN", "DAF", "Volvo". There are several modifications of the cranes. Consider the features of the node with the ability to set the lead.

The working braking of the unit is to supply air through the connection head. Power passes through the outlet of the crane to the receiver of the semitrailer. Simultaneously, the piston under pressure of the spring goes down together with the valve. Opening the outlet that connects to the working leads. After the actuation of the brakes of the tractor, the compressed air mixture flows through the connecting head into the piston chamber.

Brake control valve trailer "MAN" provides after the closure of the air outlet from the receiver through the outlets to the cylinders. Simultaneously, the mixture enters a special chamber, forming a force on the valve. After injection of the limiting pressure, the valve opens to the compression spring to compress. As a result, air enters the storage compartment, loading the lower part of the piston. After the total pressure in all chambers has reached the set limit, the piston moves upward.

Automatic braking

The brake control valve of the trailer "Volvo", when the supply line is broken, receives a sharp drop in pressure, which removes the load on the piston. Under the force of the spring, the piston moves upward, and the valve closes the outlet. The piston part with further movement releases the inlet window.

Through the terminals, the pressure from the receivers is fully applied to the brake cylinders. When the line breaks, the trailer brake control valve "Daf" works in the same way as described above. This is due to the fact that the pressure in the supply structure of the crane is also reduced due to leakage of the unit after the braking of the tractor has started.

Malfunctions

There are a number of problems that can reduce the effectiveness of the brakes. A repair kit for the brake control of the trailer may be necessary in the following cases:

• After disconnection of the heads in the main line and the opening of the disconnection valve, air from it does not reach the tractor.
• When the uncoupling valve is open, the air mixture from the head to the tractor's main line goes, but after connecting the tractor elements and the trailer dispenser, the supply stops.
• When the brakes are activated, the brakes work on the car, but there is no semi-trailer.
• In the case when air is released from the head during braking.
• In the process of disinhibition, the wheels of the prime mover are reacting, but on the trailer device they remain in the inhibited state.