To diagnose the pneumatic drive of brake systems, you must have at least one control pressure gauge and use the control output valves available on the car

Working with a single pressure gauge is very laborious, and using only standard control output valves makes troubleshooting a number of devices much more difficult.

Therefore, for an in-depth check of the pneumatic drive performance, you should use a set of control pressure gauges, as well as a set of fittings, adapters and connecting heads that allow you to measure the pressure in any line.

At the beginning, the lamps and buzzer are checked for proper operation. When you press the button in the block, the control lamps should light up.

The lamps are on if the pressure in the respective cylinders is below 4.8...5.2 kgf/cm2. The buzzer works if at least one lamp is on.

Next, after starting the engine, fill the pneumatic actuator with compressed air.

At an engine speed of 2200 rpm, a serviceable compressor pumps the brake system (lights go out) in 8 minutes.

If the filling time is longer, then the pneumatic drive may be leaking, the filter in the regulator is dirty or frozen, or the valves in the compressor are faulty.

If the cylinder-piston group is worn out, then, having a low capacity, the compressor, together with air, will supply oil to the pneumatic drive, which accumulates together with condensate in the cylinders and is thrown out of the pressure regulator.

When the pressure in the system reaches 7.0...7.5 kgf/cm2, the pressure regulator is activated, and the air from the compressor continuously exits through the atmospheric outlet. Press and release the brake pedal several times.

The pressure in the pneumatic actuator will decrease to 6.2...6.5 kgf/cm2.

The unloading valve in the pressure regulator will close, and the compressor will again increase the pressure in the pneumatic drive to 7.0...7.5 gf/cm2.

The opening and closing pressure of the valve in the pressure regulator is controlled by a two-pointer pressure gauge in the cab or by a pressure gauge connected to the control outlet valve on the condensate bottle.

Regulate the air pressure in the pneumatic drive with a screw on top of the pressure regulator.

Deviations in the operation of the pressure regulator: a sharp release of air during the filling of the system, the opening of the valve at low or high pressure and the inability to adjust it - indicate a malfunction of the device and the need for its repair.

Check the pneumatic brake actuator for leaks

When the compressor is not running and the consumers are off (the brake pedal is released, the parking brake is on), the pressure drop over 30 minutes of testing should be less than 0.5 kgf/cm2.

When the consumers are switched on (the brake pedal is depressed, the parking brake is off), the pressure drop over 15 minutes of testing must also be less than 0.5 kgf/cm2.

To check the operation of the safety valves, connect a pressure gauge to the control valve on the parking brake cylinder.

Bleed air from the front axle bottle using the condensate drain valve.

In this case, only the upper arrow of the standard pressure gauge should show the pressure drop.

The pressure in the rear bogie and parking brake cylinders should not change.

If the pressure decreases in the rear bogie cylinders, then the triple safety valve is faulty, and the pressure drop in the parking brake cylinders indicates a malfunction of the double or single safety valve (depending on the layout of the pneumatic drive) that feeds this circuit.

In order to check the operation of the pneumatic service brake actuator, you need to connect pressure gauges to the test output valves on the pressure limiter and on the rear of the frame above the rear axle.

The readings of these pressure gauges correspond to the pressure in the front brake chambers and the brake chambers of the rear bogie.

When you press the brake pedal all the way down, the pressure on the two-pointer pressure gauge should decrease by no more than 0.5 kgf / cm2 (air from the cylinders entered the brake chambers and the pressure dropped), the pressure in front brake chambers should increase to 7.0 kgf / cm2 and become equal to the upper scale of the pressure gauge in the cab.

The pressure in the rear brake chambers also increases to 2.5 ... 3.0 kgf / cm2 for an empty car.

If you lift up the vertical rod of the brake force regulator drive by the amount of static deflection of the suspension, then the pressure in the rear brake chambers should increase to 7.0 kgf / cm2 (indication the lower scale of the pressure gauge).

The static suspension deflection during loading depends on the stiffness of the springs, so for basic models it is respectively: KamAZ-5320 - 40 mm, KamAZ-5410 - 42 mm, KamAZ-5511 - 34 mm.

KAMAZ two-section brake valve drive

The drive of the brake force regulator is adjusted by changing the length of the vertical rod and changing the length of the regulator lever.

The length of the rod is set in such a way that on an empty car with the brake pedal fully depressed, the pressure in the rear brake chambers is not lower than 2.5 kgf / cm2.

The length of the governor lever is set constant for this model:

KamAZ-5320—105 mm, KamAZ-5410—105 mm, KamAZ-5511—95 mm. After releasing the brake pedal, the air from the brake chambers should exit without delay and completely.

If the nominal pressure (7.0 kgf/cm2) is not provided in the front and rear brake chambers when the pedal is fully depressed, then it is necessary, first of all, to check the correct adjustment of the mechanical drive of the brake valve (Fig. 1).

The drive has two adjustment forks: on the pedal rod and on the intermediate rod, access to the first adjustment fork is provided when the front lining is raised.

By shortening the pedal rod, we raise the pedal in the cab, the full pedal travel increases, it should be equal to 100 ... 140 mm.

When fully depressing the pedal, the lever stroke of the two-section brake valve is 31 mm.

In operation, there are cars that have a long release time, often this is due to the lack of free play of the brake pedal, which is regulated by a fork on the intermediate rod and should be 20 ... 40 mm.

If the maximum pressure in one of the service brake circuits is not ensured, and the pressure in the other is normal, then it is necessary to connect a pressure gauge to the outlet of the corresponding section of the brake valve: to the upper one - in case of poor operation of the rear bogie circuit, to the lower one - in case of poor operation of the front bogie circuit bridge.

Pressure gauges must be connected to the side (along the vehicle) outputs instead of "stop" sensors - signals on dump trucks or pipelines going to a two-wire valve on tractor vehicles.

When pressing the pedal, it is necessary to compare the pressure at the outlet of the brake valve and in the brake chambers.

When the pedal is fully depressed, the pressures at the outlet of the brake valve and the pressure limiter should be equal.

The pressure in the rear brake chambers depends on the position of the brake force regulator lever: in the lower position "empty" - 2.5 kgf/cm2, in the upper position "laden" - 7.0 kgf/cm2

Comparing the readings of pressure gauges and knowing the characteristics of the devices, you can easily find which one is faulty.

When braking with a service brake, check the stroke of the brake chamber rods.

For KamAZ-5320, 5410, 55102 cars, it is 20 ... 30 mm, KamAZ-5511, KamAZ-53212, 54112 - 25 ... 35 mm. the difference in the course of the rods of the brake chambers on one bridge is allowed - 2 ... 3 mm.

To test the operation of the parking brake circuit, you must connect a pressure gauge to the test outlet valve on the frame at the rear and check the pressure in the power accumulators.

When the parking brake valve handle is in the vertical position, the car is braked by the force of the springs in the energy accumulators, the pressure in them is atmospheric.

If you move the valve handle to a horizontal position, then the air from the parking brake cylinders will flow through the accelerating valve into the energy accumulators, the springs will compress, and the car will brake.

The pressure on the control pressure gauge should increase to 7.0 kgf/cm2.

Check the operation of the spare brake by smoothly moving the parking brake valve handle to the vertical position.

When the handle is turned up to 30°, the pressure in the energy accumulators should decrease to 5.0...4.5 kgf/cm2, and the rods of the rear brake chambers should start moving down.

Further smooth turning of the parking brake valve handle causes a synchronous decrease in pressure in the energy accumulators and extension of the rods.

When the parking brake valve handle is turned at 60...70˚, the pressure should drop to zero. If this does not happen, then it is necessary to replace the faulty parking brake valve.

When checking the function of the emergency braking circuit, apply the parking brake (atmospheric pressure in the energy accumulators).

By pressing the button of the emergency brake release valve, we bypass the air from the service brake cylinders to the energy accumulators.

When the pressure in the energy accumulators reaches 4.8...5.2 kgf/cm2, the flashing light goes out in the control lamp unit.

It takes 6...8 seconds to completely release the brakes. On manometer in the cab, the pressure drop during brake release should be no more than 0.8 kgf / cm2.

After the valve button is released, the air from the energy accumulators is completely released through the valve into the cab, the parking brake is activated.

When the parking brake is applied, a flashing light comes on in the control lamp unit.

Before checking the auxiliary brake start the engine and then press the brake valve button.

The engine should stop, as turning the lever on the high pressure fuel pump will cut off the fuel supply and close the dampers in the exhaust pipes.

The engine stop lever and dampers are actuated by pneumatic cylinders.

During auxiliary braking, air is also supplied to the normally open sensor that controls the solenoid valve on the trailer.

The valve works and passes compressed air from the trailer cylinder to the brake chambers.

The pressure in the brake chambers of the trailer is set to a constant value of 0.6. ..0.8 kgf/cm2, it is adjusted by a screw on the bottom of the solenoid valve.

To check the operation of the devices that control the trailer, it is necessary to connect a pressure gauge to the Palm head of the supply line and open the disconnect valve. In this case, the pressure gauge should show a pressure of 6.2...7.5 kgf/cm2.

Then we connect the pressure gauge to the head with the "Palm" of the control line and open the uncoupling valve.

When the tractor is disengaged, the pressure in this line is atmospheric.

If you brake the car with a service or parking brake, the pressure should increase synchronously in accordance with the angle of rotation of the parking brake valve handle or the force on the pedal from zero to 6.2...7.5 kgf/cm2

You can check the correct adjustment of the two-wire valve by locking the brake force regulator lever in the “laden” position.

In this case, the pressure in the rear brake chambers with a working regulator will be equal to the pressure in the upper, control section of the two-wire valve.

Comparing the readings of the pressure gauge measuring the pressure in the control line of the trailer and the pressure gauge measuring the pressure in the rear brake chambers with the regulator lever raised, you can determine the excess pressure.

It should be 0.6 kgf/cm2 and adjusted at a pressure of 3-4 kgf/cm2.

When screwing in the screw inside the two-wire valve, the overpressure in the control line increases.

Check the brake light sensor. The sensor contacts must close and turn on the brake lights when the pressure in the trailer control line is 0.1...0.5 kgf/cm2.

To check the operation of the brakes on a single-wire drive, it is necessary to connect a pressure gauge to the head "A" of the single-wire line and open the disconnect valve.

With the tractor disengaged, the pressure in this line should be within 4.8. ..5.3 kgf/cm2. This pressure is adjusted by a screw on the bottom of the one-way valve.

When braking with a service, parking or spare brake, the pressure in a single-wire line should decrease at full braking from 4.8...5.3 kgf/cm2 to zero.

To check the brakes on a trailer, connect pressure gauges to the control outlet valve for checking the pressure in the rear brake chambers and to the test outlet valve on the trailer cylinder.

When the trailer brakes are operated by a two-wire drive, the pressure in the cylinder should be 6.2...7.5 kgf/cm2.

When the trailer is braked with a working or parking brake, the pressure in the brake chambers increases from 0 to 3.0 kgf/cm2 if the trailer is empty.

When the regulator lever is raised to the “laden” position, the pressure should increase to 6.2...7.5 kgf/cm2.

When the solenoid valve is turned on, the pressure in the brake chambers is set to 0.6..0.8 kgf/cm2.

After release of the brakes, the compressed air must be completely discharged into the atmosphere without delay.

To transfer the trailer to work on a single-wire drive, it is necessary to close the disconnecting valves in the supply and control lines of the tractor.

As soon as the disconnect valve in the supply line closes, the compressed air from the trailer cylinder will exit through the equalizing valve in the air distributor and then through the valve to the atmosphere.

The pressure in the trailer tank should drop to 4.8...5.3 kgf/cm2, and then the trailer brakes should turn on.

The pressure in the single-line line must be equal in magnitude to the pressure in the cylinder. If these values ​​are not equal, then the closing pressure of the equalizing valve should be adjusted using the screw on the air distributor.

Connect the trailer with a single wire drive.

When braking an empty trailer, the pressure in the brake chambers must benot less than 3.0 kgf/cm2, and when the regulator lever is raised, it will increase to 4.8 ... 5.3 kgf/cm2.

If, according to the results of the check, the pressure values ​​at the control points correspond to the specified values, the pneumatic drive of the brake systems of the tractor and trailer is serviceable and operational.