The combined brake valve consists of two sections combined in one housing and is designed to control the pneumatic drive of the brakes of a tractor and a trailer (semi-trailer)

The mechanical drive of both sections is carried out by a pair of levers.

The lower section controls the brakes of the tractor vehicle, while the upper section controls the brakes of the trailer or semi-trailer.

ZIL-131 combined brake valve

Both sections have unified valves and diaphragm followers.

Two double cone valves, together with inlet seats and return springs 13, are installed in the faucet covers 18.

Two follower diaphragms 9, together with guide cups and seats 10 of the exhaust valves, are sandwiched between the valve body 8 and covers 18.

A balance spring is installed in each section, providing a follower, i.e. proportional dependence of the compressed air pressure supplied by the brake valve on the force applied to the valve drive lever.

The balancing spring 5 of the trailer section is mounted on the rod 7; its pretension is adjusted by moving the rod guide 6.

The balancing spring 20 of the tractor section is mounted in the glass 21; its preload is adjusted by shims.

Using lever 17, connected to the handbrake drive, only the trailer section can be actuated, followed by braking the vehicle with the handbrake.

The operation of the combined crane is as follows

When the pneumatic system is filled with compressed air, the latter, with the outlet valve 12 closed, through the open inlet valve 15 of the trailer section, enters the connecting line of the trailer.

When the set pressure is reached, the spring 5 is compressed and the inlet valve 15 closes the trailer line.

Then both the trailer section valves and the tractor section outlet valve remain closed.

When braking, the force from the pedal is transmitted to the drive lever 4; first, the exhaust valve 12 of the trailer section opens, while the compressed air from the trailer line is released into the atmosphere.

Then the exhaust valve closes and the inlet valve of the tractor section opens and compressed air enters the brake chambers of the tractor.

When braking, the load is removed from the drive lever 4, the exhaust valve closes, the inlet valve of the trailer section opens, and compressed air from the air cylinders enters the trailer line; at the same time, the intake valve closes, the exhaust valve of the tractor section opens, and the compressed air from the brake chambers of the tractor is released into the atmosphere.

Maintenance of the brake valve consists of periodic inspection, checking for tightness, checking the operation of the valve and cleaning it from dirt.

It is necessary to monitor the condition of the protective rubber cover and the density of fastening of the covers to the body, since the ingress of dirt into the faucet on the rubbing surfaces can lead to its failure.

It is also necessary to carefully monitor the cleaning of air in the brake system from water and oil vapors, since oil on the rubber parts of the brake valve can damage them.

For TO-2, it is necessary to check the tightness of the brake valve using a soapy emulsion.

Air leakage through the exhaust port in the braked position indicates a leak in the exhaust valve of the trailer brake control section or the inlet valve of the vehicle brake control section.

When braking, air must escape from the trailer line through the exhaust port; if air continues to escape 1-2 seconds after pressing the pedal, this indicates a leak in the intake valve of the section that controls the trailer brakes, or the exhaust valve of the section that controls the brakes of the car.

If air leakage continues after two or three repeated braking, these valves should be removed and inspected.

After 50,000-70,000 km of run, it is necessary to remove the brake valve, disassemble it, rinse the rubbing surfaces with clean kerosene, wipe them with a soft cloth and lubricate with a thin layer of grease 158 according to MRTU 12N 3 139-64.

TsIATIM-201 lubricant can be used as a substitute. In this case, lubrication must be done after 20,000-25,000 km of run, but at least once a year.

Then reassemble the brake valve, having previously checked the ease of movement of the guide cups of the diaphragms, the stem of the cups, the balancing spring and the levers.

After assembly, using guide 6 of the stem (Fig. 1), in the braked state, the air pressure in the section that controls the trailer brakes must be adjusted within 4.8-5.3 kg / cm² (pressure increases when the guide is screwed in).

After adjusting the pressure, the position of the stem guide must be fixed with a lockingnut 22.

Disassembly, cleaning and adjustment of the brake valve must be carried out by a qualified mechanic and only in a workshop.

ZIL-131 brake valve adjustment

When installing conical valves, check and, if necessary, adjust using gaskets 4 (Fig. 2) the opening of the inlet valve.

At the full stroke of the brake valve lever, the intake valve stroke should be 2.5-3.0 mm.

The opening value of the inlet valve can be measured as follows: disconnect the pipeline supplying air from the air cylinder to the brake valve, unscrew the connecting fitting from the plug 1, press the brake pedal to the full or pull lever 4 (see Fig. 1) of the brake valve (if the brake valve is removed from the car), and then with a ruler or depth gauge through the hole in plug 1 (Fig. 2) measure the stroke of the inlet valve.

Air leakage along the connector plane of the brake valve body and its covers indicates damage to the diaphragm or leaks in the parts of the valve at the point of their mating with the diaphragm. A damaged diaphragm should be replaced.


UAZ vehicles are equipped with three types of mechanical three-shaft gearboxes:

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