BELARUS-920.4/952.4 Operating manual
32
Air is taken to the pneumatic drive from the engine intake manifold through the line 8
(Figure 2.6). The air is compressed in the compressor 9 and delivered to the cylinder 13 through
the pressure regulator 11 maintaining required pressure in the cylinder. From the cylinder, com-
pressed air goes to the brake valves 3 and 16 and to the supply line 7 with the coupling head 4
(with red cap) that is always under pressure. The brake valve 3 is connected through the control
manifold 2 with the coupling head 1 (with yellow cap). There is no pressure in it. The brake valve
16 is connected through the connecting line 6 with the coupling head 5 (with black cap).
Brakes of trailers and agricultural machines are controlled in two modes: direct and auto-
matic.
When connecting a trailer with a single-wire pneumatic drive, the trailer head is connected
to the coupling head 5 (Figure 2.6) and air goes to the trailer pneumatic drive. When the brake pe-
dal is pressed on or the park brake is engaged, compressed air through the brake valve 16 is vented
from the connecting line 6 to atmosphere.
The air distributor operates on the trailer, supplying compressed air from the trailer cylin-
ders to the brake chambers, and the trailer stops. If the trailer is disconnected in case of emergency,
the coupling heads are disconnected, air from the trailer line is vented to atmosphere, and the trail-
er stops automatically.
Direct control of the brakes is performed due to pressure drop in the connecting line 6 up to
0 MPa when the tractor decelerates. In such a case, delivery of compressed air to the trailer pneu-
matic system stops.
Automatic control of the brakes (automatic braking) is performed in case of a break of the
coupling and disconnection of the trailer due to pressure drop in the trailer connecting line.
When a trailer with a two-wire pneumatic drive is used, the trailer coupling heads are connect-
ed to the coupling heads 4 (Figure 2.6) with red cap and 1 with yellow cap, i.e. to the supply line 7 and
to the control manifold 2. At that, compressed air constantly flows to the trailer through the supply line
7. When the brake pedal is pressed on or the park brake is engaged, compressed air through the brake
valve 3 and the control manifold 2 is supplied to the trailer. The air distributor operates on the trailer,
supplying compressed air from the trailer cylinder to the brake chambers, and the trailer stops.
Direct control of the brakes is performed due to pressure rise in the control manifold 2 up
to 0.65...0.8 MPa when the tractor decelerates. In such a case, the supply line 7 remains under
pressure, and delivery of compressed air to the trailer pneumatic system is preserved.
Automatic control of the brakes (automatic braking) is performed in case of a break of the
coupling and disconnection of the trailer due to pressure drop in the trailer supply line.
In the pneumatic drive, the valve coupling heads 1, 4, 5 are installed. The coupling head
valves prevent air loss in case of use of the pneumatic drive without a trailer (for example, for tire
inflation) and in case of an emergency disconnection of a trailer. When the trailer brake lines are
connected with the tractor lines, the coupling head valves open, ensuring passage of compressed
air from the tractor pneumatic drive to the trailer. At that, it is recommended to connect the pneu-
matic lines when there is no pressure in the cylinder 13 of the tractor.
Air pressure in the cylinder 13 is monitored with the air pressure indicator and the red
emergency air pressure lamp (installed on the instrument panel), the air pressure sensor 14 and the
emergency air pressure sensor 15.
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