Brake valve of MAZ car

Remove and disassemble the brake valve (Fig. 1) in the following order:

• - remove the brake pedal release spring and disconnect the brake pedal rod from the lever;

• - disconnect all pipelines from the brake valve;
• - disconnect the brake valve bracket mounting bolts and remove the brake valve;

• - unscrew the bolts and remove the base plate 32 together with the body 7 of the lever and the lever 1, remove the pusher 6;
• - remove the upper piston 30 with the balancing element as an assembly;
• - remove spring 12;
• - unscrew the bolts and separate the upper case 33 and the lower case 25;
• - remove the large piston 28 and the small piston 15 as an assembly, then remove the small piston from the large one, remove the spring 26;
• - remove the retaining ring 22 and take out the seal, the support ring, the spring 24 and the body with the valve 17 of the lower section;
• - remove the retaining ring and take out the outlet window, support ring and upper section valve assembly;
• - remove the lever 1 of the brake valve, for which remove the axle;
• - when installing the upper piston, measure the distance "C" (Fig. 2), the protrusion of the small piston shank above the valve. Using the adjusting screw on the upper piston, set the distance d = C + 0.8 mm

• - install the upper piston 30 (see Fig. 1);
• - assemble the crane with base plate and lever;
• - put on a protective cover.

After assembly, the operation of the brake valve must be checked on the stand at an air pressure in the system of 687 kPa. The scheme for testing is shown in fig. 3.

The order of checking is as follows:

• —connect piping to pins 11* and 12*. Press the lever several times until it stops (stroke S, min = 31.2 mm).

The passage of air through the terminals must be good.

With the lever released, check terminals 21*, 22* and 3* for tightness using soapy emulsion;

connect terminals 21, 22 to the cylinders. When the lever is pressed smoothly, the first circuit should operate after the lever stroke (5.7 + 1.5) mm, which corresponds to the pusher stroke (2.3 + 0.6) mm.

The initial pressure jump in the primary circuit should not exceed 20 kPa;

when the pressure in the primary circuit reaches 50 kPa, the pressure in the second circuit must be at least 245 kPa.

The advance of the pressure in the primary circuit in relation to the pressure in the second circuit can be maintained over the entire pressure range, but not exceed 25 kPa.

The initial pressure jump in the secondary circuit should not exceed 20 kPa;

• - the stroke of the lever up to a pressure of 294 kPa in the primary circuit should be (17.2d: 1.7) mm, which corresponds to the stroke of the pusher (6.9±0.7) mm;
• - the stroke of the lever up to a pressure of 687 kPa in the first and second circuits should be (24 ± 2.4) mm, which corresponds to the stroke of the pusher (9.6 ± 1) mm;
• - the total stroke of the lever to the stop should be (34.6 ± 3.5) mm, which corresponds to the stroke of the pusher (13.9 + 1.4) mm;
• - when the lever is smoothly pressed, after the initial jump, in each circuit, the pressure should gradually increase, and when released, it should gradually decrease. The pressure reduction steps must not exceed 294 kPa;
• —in case of failure of the first or second circuit, the remaining circuit must remain fully operational;
• — check the valve for leaks in the inlet position.

The crane is installed on the car in the reverse order of removal. It is possible to install a brake valve (Fig. 4).

Crane of brake modification No. 2

Remove and disassemble the brake valve (Fig. 4) in the following order:

• - raise the car cab;
• - disconnect all pipelines from the brake valve;
• - unscrew the bolts 27 and remove the brake valve, preventing the pusher 1 from falling out;
• - take out the upper piston 25 with the elastic element 26 as an assembly;
• - remove spring 7;
• - unscrew the bolts and separate the upper case 28 and the lower case 20;
• - remove spring 21, large piston 23 assembled with small piston 10, and then remove small piston from large;
• - remove the retaining ring 17 and take out the atmospheric outlet housing 18 with sealing rings, the support ring 14, the spring 19 and the valve of the lower section 12;
• - remove the retaining ring and take out the seal, support ring 9, spring 8 and valve of the upper section ii 24.

Assemble the crane in the reverse order of disassembly.

Before installing the upper piston, measure the distance "C" (Fig. 2) - the protrusion of the small piston shank above the valve.

Using the adjusting screw on the upper piston, set the distance d = c + 0.8 mm and fix the adjusting screw.

After assembly, it is necessary to check the operation of the brake valve on the stand at an air pressure in the system of 0.7 MPa (7.0 kgf / cm²).

Scheme for testing is shown in fig. 5.

The order of checking is as follows:

• - connect pipelines, plug unused outputs. Press the pusher three times until it stops.

With the pusher released, check terminals 21,22 and 23 for tightness using soapy emulsion;

• - connect pins 21 and 22 to the cylinders and gently press the pusher.

The first circuit (upper) should operate after the pusher stroke of 1.9-3.0 mm. The initial pressure jump should not exceed 0.02 MPa (0.2 kgf/cm²);

• - when the pressure in port 21 reaches 0.05 MPa (0.5 kgf/cm²), the pressure in port 22 must be at least 0.025 MPa (0.25 kgf/cm ²).

The advance of the pressure in port 21 relative to the pressure in port 22 can be maintained over the entire pressure range, but not exceed 0.025 MPa (0.25 kgf/cm²).

The initial pressure surge at port 22 must not exceed 0.02 MPa (0.2 kgf/cm²).

• when a pressure of 0.3 MPa (3.0 kgf/cm²) is reached in outlet 21, the stroke of the pusher should be (5.8—8.0) mm;
• when a pressure of 0.75 MPa (7.5 kgf/cm²) is reached in outlet 21, the stroke of the pusher should be (8.4—10.8) mm;

the total stroke of the pusher to the stop should be (12.5-15.7) mm;

• - when the pusher is smoothly pressed, after the initial jump, in each circuit, the pressure should gradually increase, and when released, it should gradually decrease;
• — check the tightness of the tap with the pusher pressed all the way;
• - check the tightness with the pusher of the first circuit pressed all the way down in the absence of pressure in the second circuit, and then the tightness of the second circuit in the absence of pressure in the first.

Installing the faucet in reverse order.