In this article, we will consider the pneumatic actuator of the trailer brakes, i.e., the interaction and malfunctions of devices installed on the tractor and on the trailer

First, consider the option of connecting the brake systems of the tractor and. trailer on a two-wire drive.

If the trailer tank does not fill with air, first check the correct connection of the supply and control lines.

Let's look at malfunctions that cause no air supply to the sight cylinder, and how to detect these malfunctions.

After disconnecting the connection heads in the supply line and opening the disconnect valve, no air comes out of the connection head on the tractor

After connecting a pressure gauge to the control valve on the parking brake cylinder, check the air pressure in the cylinder.

If the pressure in the cylinder is less than 5.4-5.6 kgf / cm2, the single protective valve does not let air into the supply line - you need to find out the reason why the pressure does not rise above the specified value

Even if the pressure in the cylinder is more than 5.6 kgf / cm2, air ducts may be blocked, incorrect adjustment or malfunction of the single protective valve, malfunction of the disconnect valve.

When the disconnect valve is open, air flows from the connecting head in the supply line of the tractor, but after connecting the heads of the tractor and the trailer, air does not enter the supply inlet of the air distributor

The reason for this is blockage of air ducts or heavy pollution, and in winter, icing of the main filter.

If air is supplied to the air distributor, but does not enter the cylinder, the air distributor is faulty or the air line from the device to the cylinder is clogged.

When the road train brakes, the brakes on the tractor are applied, but not on the trailer.

Disconnect the "Palm" heads of the control line, open the disconnect valve, press the brake pedal.

If compressed air does not come out of the head, then the trailer brake control valve with a two-wire drive is faulty.

It is also possible to block the lines from the parking brake cylinders to the trailer brake control valve or from the valve outlet to the release valve and the connecting head of the control line.

If air escapes from the Palm head of the tractor control line when braking, then the drive on the trailer is faulty, the pipelines do not let air through, the main filter is clogged or iced over, the air distributor, solenoid valve or brake force regulator are faulty .

Faults can be determined more accurately by successively shutting down pipelines and devices.

First, the control line from the connecting head to the air distributor is checked, and then the supply line from the air distributor to the brake chambers.

When the road train is released, the wheels of the tractor are released and the trailer remains in the braked state

Close the disconnect valve in the control line, if after that the air from the line escaped into the atmosphere through the atmospheric outlet of the valve, and the trailer braked, then the trailer brake control valve with a two-wire drive is faulty.

The valve does not release air into the atmosphere when released due to jamming of the upper piston or piston rod in the middle part of the device.

If, when the release valve is closed, air is not released into the atmosphere through the valve, since it has already escaped into the atmosphere through the trailer brake control valve, the air distributor, solenoid valve or brake force regulator are faulty.

Air is expelled from the atmospheric outlet of the 2-wire trailer brake control valve when the service or parking brake is applied

In this case, the sealing rings or the valve in the device itself are leaking.

After releasing, air continues to flow out of the atmospheric outlet of the two-wire valve.

Faults are possible in the device itself (valve sleeve seals), in the trailer brake control valve with a single drive drive (rod seals in the piston or piston in the guide), in the air distributor (upper piston pusher seal).

To find a faulty device, disconnect the Palm heads of the control line, if the air leakage from the two-wire valve has stopped, and is observed from the trailer head, then the air distributor is faulty.

If the faulty device is not found at this stage of the test, close the disconnect valve in the control line and disconnect the control line at the two-wire valve.

Atmospheric outlet of the 2-wire valve continues to leak, which means it is defectiveen.

Air leak has started from a disconnected line —► the single-wire trailer brake control valve is faulty.

If air leaks from the atmospheric outlet of the air distributor during braking, the device itself is faulty (the exhaust valve is leaky).

If air leaks from the atmospheric outlet of the air distributor after releasing the brakes, the malfunction may be both in the device itself and in the solenoid valve.

You can detect a faulty device by disconnecting the line between the air distributor and the solenoid valve, if the leakage through the air distributor continues - the air distributor is faulty, it started from the disconnected line - the solenoid valve.

Malfunctions that occur when the trailer brakes are controlled by a single-wire drive

The road train is disengaged and the trailer tank is not supplied with air

The reason may be a malfunction or incorrect adjustment of the single safety valve, a blockage in the pipelines through which air is supplied to the trailer brake control valve with a single-line actuator, a malfunction of this valve or a disconnect valve.

It is also necessary to bear in mind the following: if the trailer brake control valve with a two-line actuator does not bleed air from the control line after releasing the brakes, then the trailer brake control valve with a single-line actuator does not resume air supply to the single-line line.

To check the completeness of air discharge from the control line, disconnect the heads in this line, close the disconnect valve and apply the parking or service brake on the tractor, and then release the brakes.

After that, open the disconnect valve in the control line, if the air does not come out of the Palm head, the trailer brake control valve with a two-wire drive is in good condition and ensures complete air release when released.

If, when the tractor is unbraked, air comes out of the type “A” coupling head, the tractor’s single-wire line is OK.

The reason for the lack of air in the trailer cylinder must be sought on the trailer itself: it is necessary to check the condition of the main filter, dual-line valve, air distributor, pipelines.

So, for example, if the sealing washer in a two-line valve is leaking, air will pass through the valve into the supply line, and through the atmospheric outlet of the closed disconnect valve in this line it will escape into the atmosphere.

After braking, air escapes from the atmospheric outlet of a single-line valve - the valve itself is faulty (the diaphragm is broken or the upper thrust ring of the pusher or air distributor is broken).

A breakage is easily detected when disconnecting the heads of a single-wire line or closing the disconnect valve.

If the one-way valve continues to leak after this, the valve is faulty. In case of leakage from the head with "B" or through the atmospheric outlet of a closed disconnect valve, the air distributor must be repaired.

Let's consider the case when, when braking a road train operating on a single-wire drive, the trailer brakes are applied with a delay and only after a significant amount of air has been discharged from the atmospheric outlet of the single-wire valve.

The reason is the inconsistency between the pressure regulation in the single-wire actuator (the screw on the bottom of the single-wire valve) and the equalizing valve (the screw on the air distributor).

In this case, the closing pressure of the balancing valve is less than the pressure in the single-line line and in the trailer tank.

During braking, the air from the trailer's tank escapes until the equalizing valve closes, and the trailer brakes only after the valve is closed.

If the closing pressure of the equalizing valve is greater than in a single-line line, then after switching from a two-line drive to a single-line drive, the pressure in the trailer cylinder will remain higher than in a single-line line, and such a trailer can only be braked after the pressure in the cylinder is reduced using condensate drain tap.