Faults in pneumatic drive power devices

When servicing the pneumatic brake drive of a car, you must first of all make sure that the system is tight

Particular attention should be paid to the tightness of the connections of pipelines and flexible hoses, since air leaks most often occur here

Points of strong air leakage are determined by ear, and weak ones - with the help of a soap emulsion.

Air leaks from pipeline connections and brake system devices are eliminated by tightening them, and leaking pipelines and flexible hoses are replaced.

It must be remembered that on vehicles manufactured since March 1986, pipeline connections are sealed using rubber rings, so the tightening torques of the fittings should be less (table 1).

If the air cylinders of the pneumatic drive of the brakes are not filled, and the pressure regulator releases air into the atmosphere, then there may be several reasons:

  • - the pipeline between the regulator and safety valves is blocked;
  • - the pressure regulator is faulty - most often the filter element is clogged with oil or ice crystals.

If the air tanks fill slowly and the air pressure does not reach the nominal value, then either the compressor or the pressure regulator is faulty.

An increased oil content in the condensate indicates a malfunction of the piston-cylinder group of the compressor.

The cylinders of a separate circuit are often poorly filled. The air in each circuit of the brake system passes through the section of "its" protective valve.

Probably, the safety valve does not let air into the cylinder or the air supply pipe to this circuit is clogged. It is also possible that the regular two-pointer pressure gauge is faulty.

Malfunctions of the service brake system

Inefficient braking of the car when the brake pedal is pressed occurs if the brake valve drive is misaligned or the two-section brake valve is faulty.

If, during braking, the pressure in the brake chambers is nominal, then the wheel brake mechanisms are misadjusted or faulty.

If, when braking with a service brake, the pressure is below normal only in the brake chambers of the front axle, then either the lower section of the brake valve or the pressure limiter is faulty.

If the pressure in the brake chambers is normal, but the braking is not effective, then the stroke of the brake chamber rods is more than normal, or, for example, the brake linings are oiled.

When you press the brake pedal, the braking of the wheels of the rear bogie is ineffective or does not occur at all (the front wheels brake normally).

In the pneumatic part of the drive, the upper section of the brake valve or the brake force regulator may be faulty. In the mechanical part, the brake mechanisms or the drive of the brake force regulator lever are faulty or misadjusted.

If, after releasing the brake pedal, all the wheels of the car do not brake, then the two-section brake valve is faulty (the pusher or upper piston is jammed). It is possible that the drive of the brake valve is out of adjustment (there is no free play of the brake pedal).

If air does not escape from the rear brake chambers after releasing the brake pedal, the brake force regulator or the upper section of the brake valve is faulty.

These malfunctions lead to a delay in the discharge of air from the front brake chambers.

If, when releasing air, only the front brake chambers do not release air, then the pressure limiter or the lower section of the brake valve is faulty.

Air leaks from the atmospheric outlet of the pressure limiter or brake force regulator during braking indicate a malfunction of these devices.

The reason for air leaks from the atmospheric outlet of a two-section brake valve can be not only sealing rings and valves in the valve itself, but also other devices of the brake system.

If air leakage from the atmospheric outlet of the brake valve is observed when the pedal is released and the parking brake is applied, then the brake valve is faulty.

When the engine is not running, using a regular two-needle pressure gauge, you can accurately determine which section of the valve is leaking: if the upper arrow of the pressure gauge falls, the lower section of the valve is leaking; the lower arrow falls - the upper section is leaking.

If air leakage from the atmospheric outlet of the brake valve is observed only when the parking brake is released, and stops when it is turned on, then the trailer brake control valve with a two-wire drive or one of the energy accumulators is faulty.

You can identify a faulty device by supplying air to the power accumulators from the emergency release circuit: if the brake valve continues to leak when the emergency release valve button is pressed, then the seal of the pusher in the battery housing is leaking, and if there is no leakage, then the diaphragm in the trailer brake control valve is faulty.

Air leakage from the atmospheric outlet of the brake valve during braking indicates leakage of valves or sealing rings in the device itself.

Faults in the pneumatic drive of the parking brake system and the emergency release circuit

If, when the parking brake is released, the wheels of the rear bogie are not released, then the reason for this may be a malfunction in the parking brake valve, in the accelerating or dual-line valves, in the energy accumulators.

It is possible that one of the pipes in the parking brake circuit is clogged, frozen, or pinched.

In the parking brake valve, a broken plastic guide plate or unreliable fastening of the rod to this plate leads to non-braking of the parking brake.

In the relay valve in winter, the most likely cause of non-release is the freezing of condensate in the cavity above the piston.

If one of the energy accumulators does not work when moving the parking brake valve handle, then mechanical damage to this device is possible: dents in the case or jamming of the pusher.

It is also possible to block the pipeline through which air is supplied to a non-working energy accumulator.

If the rods of the brake chambers come out when the energy accumulators are turned on, and the car does not brake efficiently enough, then it is necessary to check the stroke of the rods (it should not exceed 40 mm) and the serviceability of the brake mechanisms of the wheels.

Brake pads must not be worn or oily.

The most common malfunctions in the parking brake circuit, as in the entire pneumatic drive, are compressed air leaks due to malfunctioning sealing rings, cuffs.

It is important to determine the cause of the leak, to find the faulty device.

A leaky stem seal in the guide leads to air leakage from under the parking brake valve handle when releasing the brakes.

This seal is the fastest to fail because the stem reciprocates and rotates and the O-ring diameter is small.

The cause of air leakage from the atmospheric outlet of the parking brake valve is not always the leakage of seals in the valve itself. It is possible that the trailer brake control valve with a two-wire drive is faulty.

How to identify a faulty device? Fill the pneumatic drive with compressed air, turn on the parking brake, disconnect the control line from the valve, if air leakage from the atmospheric outlet continues, then the parking brake valve is faulty; if a leak is observed from a disconnected control line, then the trailer brake control valve is faulty.

If air leaks from the atmospheric outlet of the relay valve both during braking and when the parking brake is released, the sealing ring of the atmospheric outlet of the valve is leaking.

Air leakage through the atmospheric outlet of the device when braking with a parking brake is caused by the loss of tightness of the inlet valve, and when released, the exhaust valve. In the latter case, the release of the rear wheels is not provided.

Sometimes air leakage through the relay valve is observed when the parking brake is applied and the brake pedal is simultaneously depressed.

In this case, one of the energy accumulators is faulty - air from the brake chamber through the seal of the pusher pipe goes into the energy accumulator and then through the accelerating valve into the atmosphere.

During operation in power accumulators, the piston seals in the cylinder and the pusher pipes in the housing wear out and fail.

When the parking brake is released, compressed air from under the piston through a leaky seal enters the cavity above the piston and through the connecting hose from the side of the device under the diaphragm of the brake chamber, and from there into the atmosphere through the drain hole.

When the parking brake is applied, the leakage stops.

If the seal of the pusher pipe in the energy accumulator housing fails, then when the parking brake is turned off, compressed air from under the piston enters the cavity above the diaphragm and escapes into the atmosphere through the brake force regulator.

If the regulator lever is "tied" in the up position or the car is fully loaded, then the air is released into the atmosphere through the atmospheric outlet of the brake valve.

To detect a faulty energy accumulator, after releasing the parking brake, one by one disconnect the pipelines supplying compressed air to the rear brake chambers: for a faulty device, compressed air will come out of the brake chamber cavity.

Springs in energy accumulators can be compressed mechanically using the screws located on top.

When the screw is turned out, the force is transmitted through the thrust bearing to the piston, and the spring is compressed.

If the threaded connection of the screw and the boss are not lubricated, and the screw is not tightly screwed into the boss, and moisture gets into the threaded connection, the thread rusts, it becomes difficult, and sometimes impossible, to unscrew such a screw.

You can brake the power accumulators using the emergency brake release circuit.

When the emergency release valve button is pressed, compressed air from the service brake cylinders is supplied through a two-line valve to the energy accumulators.

If, when the valve button is pressed, the energy accumulators are not released, and after it is released, a small portion of compressed air comes out of the atmospheric outlet, then the pipeline section between the valve and the two-line valve is blocked.

If, after releasing the valve button, there is no air outlet from the atmospheric outlet, then the valve itself is faulty.

If, when the tap button is pressed, air escapes into the atmosphere through the accelerating valve, the two-way valve is faulty, the sealing washer is leaking in it.

Air leakage from the atmospheric outlet of the emergency brake release valve may be due to a malfunction of both the valve itself and the two-line valve.

If air leakage is observed regardless of the position of the parking brake valve handle, then the valve itself is faulty.

And if the leak occurs only when the parking brake is released, and stops when braking, then the two-way valve is leaking.

In both cases, it is forbidden to plug the atmospheric outlet in the emergency brake release valve with a plug, as this will cause spontaneous release of the vehicles parking brake and the emergency brake will not work satisfactorily.

This is explained by the fact that when the emergency or parking brake is turned on by turning the handle of the parking brake valve, air is not always released from the energy accumulators.

Air release is prevented by a dual-line valve, and a faulty emergency release valve creates enough air pressure in the power accumulators to release the parking brake.

The following are the most likely malfunctions that a driver can detect and fix without using diagnostic equipment

If the air reservoirs are not filled, and the pressure regulator vents air into the atmosphere, then there may be several reasons for this malfunction:

  • - the pipeline between the regulator and safety valves is blocked;
  • - the pressure regulator is faulty - most often the filter element is clogged with oil or ice crystals (in winter).

If the receivers fill slowly and the pressure in them does not reach the nominal value (in the absence of leaks), then either the compressor or the pressure regulator is faulty.

If the receivers of a separate circuit are poorly filled, then, first of all, you should pay attention to the safety valve section of this circuit.

Inefficient braking of the car by the service brake occurs if the drive is misaligned or the two-section brake valve is faulty.

If, during braking, the pressure in the brake chambers is nominal, then the brake mechanisms are out of adjustment or faulty.

If, when braking with a service brake, the pressure is below normal only in the brake chambers of the front axle, then either the lower section of the brake valve or the pressure limiter may be faulty.

If the pressure in the brake chambers is normal, and braking is inefficient, then the cause of this malfunction may be a large stroke of the brake chamber rods or, for example, oily brake pads.

If, when the brake pedal is depressed, the braking of the wheels of the rear bogie is ineffective or does not occur at all, while the front wheels brake normally, then the upper section of the brake valve may malfunction in the pneumatic part of the drive or the brake force regulator is faulty. In this case, violations of the adjustments of the brake mechanisms or the drive of the brake force regulator are possible.

If, after lowering the brake pedal, all the wheels of the car do not brake, the two-section brake valve may be faulty (the pusher or upper piston is jammed) or the brake valve drive is misaligned (there is no pedal free play).

If, after releasing the brake pedal, air does not come out only from the rear brake chambers, then it is possible that the brake force regulator or the upper section of the brake valve is faulty.

These malfunctions lead to a delay in the discharge of air from the front brake chambers. If, when releasing, air is not released only from the front brake chambers, then the pressure limiter or the lower section of the brake valve is faulty.

The cause of air leaks through the atmospheric outlet of a two-section brake valve can be not only sealing rings and valves in the valve itself, but also other devices of the brake system.

If a leak is observed when the pedal is released and the parking brake is on, then the brake valve is faulty.

According to the regular two-needle pressure gauge, you can accurately determine which section of the valve is leaking: if the upper arrow of the pressure gauge “falls” when the engine is not running, then the lower section of the valve is leaking; the lower arrow “falls” - the upper section is leaky.

If air leakage through the atmospheric outlet of the brake valve is observed only when the parking brake is released, and stops when it is turned on, then the trailer brake control valve with a two-wire drive or one of the energy accumulators is faulty.

It is possible to identify a faulty device by supplying air to the energy accumulators from the emergency braking circuit: if the brake valve continues to leak when the emergency release button is pressed, then the pusher seal in the energy accumulator housing is leaking, and if there is no leakage, then the membrane in the trailer brake control valve is faulty .

If the wheels of the rear bogie do not release when the parking brake is released, then the cause of this malfunction may be the parking brake valve, accelerator or dual-line valve and energy accumulators.

It is possible that one of the pipes in the parking brake circuit is clogged, frozen, or pinched.

If one of the energy accumulators does not work when moving the parking brake valve handle, then the cause may be dents on the body or jamming of the pusher.

It is also possible to block the pipeline through which air is led to a non-working energy accumulator.

If the rods of the brake chambers come out when the energy accumulators are turned on, and the car does not brake efficiently enough, then it is necessary to check the stroke of the rods and the serviceability of the brake mechanisms and wheels.

The most common malfunctions in the parking brake circuit, as in the entire pneumatic drive, are compressed air leaks due to damage to the sealing rings and cuffs.

A leaky stem seal in the guide leads to air leakage from under the parking brake valve handle when releasing the brakes.

The cause of air leakage from the atmospheric outlet of the parking brake valve is not always the leakage of seals in the valve itself.

For example, there may be a leak due to a defective 2-wire trailer brake control valve.

To determine the faulty device, fill the pneumatic drive with compressed air, turn on the parking brake, disconnect the control line from the valve.

If, at the same time, air leakage from the atmospheric outlet continues, then the parking brake valve is faulty; if a leak is observed from a disconnected pipe, then the trailer brake control valve is faulty.

If air leaks from the atmospheric outlet of the relay valve during braking and when the parking brake is released, then the sealing ring of the atmospheric outlet of the valve is leaking.

Air leakage through the atmospheric outlet of this unit when braking with a parking brake is caused by the loss of tightness of the inlet valve, and when released, the exhaust valve. In the latter case, the release of the rear wheels is not provided.

Sometimes air leakage through the relay valve is observed when the parking brake is applied and the pedal is depressed at the same time.

In this case, one of the energy accumulators is faulty - air from the brake chamber enters the energy accumulator through the seal of the pusher pipe and then through the accelerator valve into the atmosphere.

During operation in power accumulators, the piston seals in the cylinder and the pusher pipes in the housing wear out and fail.

When the parking brake is released, compressed air from under the piston through a leaky seal enters the cavity above the piston and through the connecting hose on the side of the device under the brake chamber membrane, and from there into the atmosphere through the drain hole. In this case, when the parking brake is applied, the leakage stops.

If the seal of the pusher pipe in the energy accumulator housing fails, then when the parking brake is applied, compressed air from under the piston enters the cavity above the membrane and escapes into the atmosphere through the brake force regulator.

If the regulator lever is in the upper position, then the air is vented to the atmosphere through the atmospheric outlet of the brake valve.

To detect a faulty energy accumulator, after releasing the parking brake, one by one disconnect the pipelines supplying compressed air to the rear brake chambers: for a faulty device, compressed air will escape from the cavity of the brake chamber.

If and when the emergency release button is pressed; the energy accumulators are not released (at a pressure in the pneumatic drive of more than 500 kPa), and after it is released, a small portion of compressed air comes out of the atmospheric outlet of the pneumatic valve, which means that the pipeline section between the valve and the two-line valve is blocked.

If, after releasing the air outlet button, there is no atmospheric outlet, then the valve itself is faulty.

If, when the tap button is pressed, air escapes into the atmosphere through the accelerator valve, then the two-way valve is faulty.

Air leakage from the atmospheric outlet may occur due to a malfunction of both the tap itself and the two-way valve.

If air leakage is observed regardless of the position of the parking brake valve handle, then the valve itself is faulty.

But if the leak occurs only when the parking brake is released, and stops when braking, then the two-way valve is leaking

In both cases, it is forbidden to plug the atmospheric outlet in the emergency release valve with a plug, as this will cause spontaneous release of the parking brake, and the vehicles emergency brake will not work satisfactorily.

This is explained by those. that when the emergency or parking brake is turned on by turning the handle of the parking brake valve, it will be difficult or impossible to release air from the energy accumulators.

If, when the auxiliary brake valve button is pressed, the engine does not stop (the dampers in the exhaust pipes do not turn), and the trailer does not slow down, then there may be several reasons explaining this phenomenon: air is not supplied to the auxiliary brake valve, the pipeline is pinched or clogged , going from the crane to the pneumatic cylinders, the crane itself is faulty.

The malfunction is determined by successive disconnection of pipelines.

If the fuel does not turn off when the auxiliary brake is applied, and the dampers in the exhaust pipes operate, then you should check whether compressed air is supplied to the pneumatic cylinder on the fuel pump. A malfunction is also possible in the mounting of the pneumatic cylinder.

The damper mechanism and the pneumatic cylinders that control them operate in the most unfavorable conditions. Therefore, they fail more often than others, most often the dampers jam.

If this happens with both dampers, then the engine will not start, if with one, then the engine starts, but smokes and does not develop power.

There may also be malfunctions in the damper drive pneumatic cylinders, the most common of which is the loss of tightness of the piston cuff.

The trailer solenoid switch is located on the left side member of the frame inside, next to the clutch housing.

If the sensor or electrical wiring fails and when the auxiliary brake is turned on, the trailer does not brake, and the road train may skid and fold.

If, after releasing the button of the auxiliary brake valve, the air from the pneumatic cylinders and the sensor is not released, i.e. the auxiliary brake does not turn off, then you need to check the atmospheric outlet in the valve.

In winter, it often freezes over, a mud-ice plug forms in the atmospheric outlet, which does not allow air to escape from the circuit.

If in this case the inlet valve in the auxiliary brake valve loses its tightness, the brake will turn on spontaneously, and the engine will stop for no apparent reason.

If there is no air in the auxiliary brake circuit, the engine can be started, but after a few minutes it spontaneously stops due to the air supply through a faulty valve to the fuel shut-off air cylinder. Such a crane needs to be replaced.

If there is no spontaneous engine stop, but it does not start after the auxiliary brake valve button is released while the car is moving, then it is enough to clean the atmospheric outlet of the valve.