A standard trailer brake control valve is used to control the brakes of a semi-trailer when a similar tractor system is activated. In addition, he is responsible for the automatic operation of the brakes in the event of a critical pressure drop in the line. The drive of this unit is a combined type (single and two-wire). Consider the design features, device and connection devices.
Short description
The trailer brake control valve consists of the following elements:
- A paired control valve and similar single element.
- Two disconnecting taps.
- A pair of connecting heads.
The valve is responsible for controlling the brakes of the semi-trailer, directs compressed air from the input source to subsequent consumers, working both synchronously and separately. Two conclusions are given a command to increase the pressure in the line, and the reverse action is applied to one analogue, which affects the decrease in pressure when the air mixture is released by means of a manual lever.
Check valve
The trailer brake control valve is equipped with a main valve, which consists of three sections, a large and a small piston with springs. The middle piston element has an inlet valve, which compresses the spring to the seat.
The remaining components of the part in question:
- Diaphragm.
- Discharge port.
- Stock.
- Adjusting screw.
In the disinhibited position, compressed air is constantly supplied to the output parts. It acts on the diaphragm and piston, holds it together with the rod in the lower position. This contributes to the increased diaphragm area. At the top, the piston group is located in the extreme upper position, and the exhaust valve is separated from the seat. The intake analog is in a closed state under the influence of a spring. One of the terminals connects the brake control line to the atmospheric outlet by means of discharge openings and a rod.
Valve operation during braking
The valve of the KamAZ trailer brake control valve during braking delivers compressed air from the sections of the device to the terminals. From the other outlet of the air reservoir, the compressed mixture enters the control terminal, after which it is sent to the main part. There, air acts on the piston until it is balanced under the upper pressure from below. The upper piston operates under the force of air pressure and a spring. In this case, the middle piston should also be balanced under the influence of identical factors. In principle, a common follow-up action occurs.
During disinhibition, compressed air is discharged through the atmospheric opening of the valve from the filled compartments. Pistons under pressure of the spring and air mixture become in the upper position, and the piston rod moves down. The valve is detached from the seat and connects the internal and external inputs.
Suitable compressed air forces the piston rod to move separately upward, and the large and small piston element downward. Subsequent operation of the brakes occurs according to a similar principle.
When the truck’s spare or parking system is activated, compressed air is supplied through an atmospheric opening in a manual reverse valve and exits. The degree of pressure above the diaphragm decreases, reducing the force exerted on the working elements. The saddle abuts the valve, separating the output terminal with the atmosphere. Then the valve opens, communicating between itself the output and the main line.
Features
In the trailer brake control valve, the main pressure is pumped up until the force acting on the piston from below is balanced with the action applied to the diaphragm. This ensures follow-up operation of the valve.
When the compressed air mixture simultaneously approaches the working terminals, and the pressure in the compartment connected to the line, and the pressure exceeds the same value in the control terminal (20-100 kPa), the leading action of the brakes is carried out. The value of the required pressure indicator is adjusted using the adjusting screw, 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 decrease in this indicator in the supply line of the semi-trailer. In addition, it prevents the leakage of compressed air from the system during an emergency decrease in pressure in the vehicle’s drive, which prevents unauthorized braking of the hitch.
A single valve is adjusted for 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, she goes to the exit of the main highway. The value of the required pressure indicator is carried out by the adjusting screw.
Uncoupling tap
This part is involved in the operation of the trailer brake control valve as follows:
- It, if necessary, closes the pneumatic line, aggregating the tractor with a towing device.
- If you install the handle of the device along the axis of the crane, the pusher with the rod will be in the lower position, and the valve will be open. The compressed air through it and the corresponding output goes from the car to the semi-trailer.
- When placing the handle across the core, the rod and diaphragm move upward under the influence of air pressure and the spring. The valve blocks the conclusions, sitting in the saddle. The air mixture flows 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 accessories.
- a - the device is not active;
- b - the position of the open crane;
- 1 — output to the control valve of the tractor’s air cylinder through a single protective valve;
- II - The main conclusion of the trailer brake system ;
- III - atmospheric output;
- 1 - spring mechanism;
- 2 - valve;
- 3 — aperture with a rod;
- 4 - return spring;
- 5 - a pusher with a handle.
Palm Connection Heads
It is these parts of the KamAZ trailer brake control valve that are also used in MAZ and Ural systems. The elements serve to combine the highway of the double-circuit pneumatic drive of the vehicle TC and the semi-trailer. They are valveless heads; a rubber seal is used to seal the butt joints. The design of the assembly also includes clamps, which are responsible for holding the parts in an adhered state.
Single wire system
Unlike a two-wire trailer brake control valve, this design consists of a control valve, an uncoupling analogue and a connecting L-shaped head.
The brake control valve with a single-wire actuator operates through a single line, which is used as a supply and control system. It is worth noting that the valve operates to lower the pressure in the main line, with the possibility of bringing the indicator to an atmospheric parameter. When the pressure decreases, the braking intensity of the hitch increases. Other parts of the crane include: a pusher with a diaphragm, a piston of a stepped type, valves (inlet and outlet). Between themselves, they aggregate by connecting rod. There is also a lower piston.
Work in disinhibited condition
In the inactive position, the compressed air enters 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 the power spring, the diaphragm and pusher are located in the lower position. The exhaust valve remains closed, and the inlet analog works open, passing air 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 the fact that the area of the stepped piston is larger, it moves up to the stop. When the pressure in the chamber of the trailer brake line is about 500-520 Pa, the lower piston goes down and blocks the intake valve. In the uninhibited state, the system automatically maintains a pressure level of 500 Pa, which is slightly lower than the same parameter in the pneumatic drive of the truck.
How does the system function when braking?
When the tractor brakes are activated, compressed air from a double-circuit valve enters the valve of a single-wire MAZ trailer brake control valve. The mixture fills the plane below the diaphragm. After overcoming the spring force, the diaphragm moves upwards along with the pusher, the intake valve closes, the exhaust element opens. Air escapes into the atmosphere, bypassing a special outlet, pusher and hole in the lid.
A stepped piston carries out a follow-up action. If the pressure at the outlet and in the cavity decreases, the force of action on the piston from the bottom 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, entraining the pusher, which closes the outlet window with its saddle. A subsequent increase in pressure causes the complete release of the air mixture from the main brake design of the semi-trailer. The pusher is at the same time in the lowest position, the intake window is blocked, the exhaust element is open.
Variable mode
The connection of the trailer brake control valve implies the normal operation of all components of the device. The single-wire version, when the tractor brakes are relaxed, interacts with the atmosphere through the provided valve hole of the two-wire drive. The pressure in the working cavity decreases, and the diaphragm with the pusher moves to its original position, blocking the exhaust valve and opening the inlet element. Compressed air enters the outlet and trailer coupling system, releasing it.
The L-shaped coupling head aggregates with the single-wire drive line, automatically closing the truck's coupling system in case of spontaneous separation of the heads, which can happen when the trailer is uncoupled. The head is equipped with a valve that is 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 crane
It is with such designs that trailers are connected that are connected to machines of the MAN, DAF, and Volvo brands. There are several modifications of cranes. Consider the features of the node with the ability to set the lead.
Working braking of the assembly consists in supplying air through the connecting head. Power passes through the tap outlet to the receiver of the semi-trailer. Synchronously, the piston, under spring pressure, goes down with the valve. Opening the outlet that connects to the work leads. After the tractor brakes are activated, the compressed air mixture enters through the connecting head into the piston chamber.
Crane brake control trailer "MAN" delivers after closing the outlet air from the receiver through the outlets to the cylinders. At the same time, the mixture enters a special chamber, which forms a force on the valve. After pumping up the limiting pressure, the valve opens towards compression by the spring. As a result, air enters the storage compartment, loading the lower part of the piston. After the summed pressure in all chambers reaches the set limit, the piston is fed up.
Auto braking
The brake control valve of the Volvo trailer, when the supply line breaks, gets a sharp decrease in pressure, as a result of which the piston is relieved of stress. Under the force of the spring, the piston moves up, and the valve blocks the outlet. The piston part with further movement releases the inlet window.
Through the findings, the pressure from the receivers fully flows to the brake cylinders. When the main line breaks, the Daf trailer brake control valve operates according to a similar scheme, which is described above. This is due to the fact that the pressure in the supply structure of the crane also decreases due to leakage of the unit after the tractor starts braking.
Malfunctions
There are a number of problems that can reduce the effectiveness of the brakes. A repair kit for the trailer brake control valve may be needed in the following cases:
- After the heads are disconnected in the main highway and the uncoupling valve is opened, air from it does not enter the tractor.
- When the uncoupling valve is open, the air mixture flows from the head to the tractor line, but after connecting the tractor elements and the trailer distributor, the flow stops.
- When brakes are activated, the brakes on the car work, but not on the semi-trailer.
- In the case when air comes out of the head during braking.
- In the process of disinhibition, the tractor wheels react, and on the towing device remain in a locked state.