109
When depressing the brake pedal, the effort is transferred through the levers and drive
rods system on the lever 1 of the valve and further via pusher 6, disk 8 and resilient member to
follow-up piston 25. Lowering down, the piston 25 first closes the valve 24 outlet hole of the
brake valve upper section, and then opens up the valve 24 from the seat in the upper part 11,
opening the passage for the compressed air from the outlet V
1
to the outlet Z
1
and further to the
operation units of one of the contours. The pressure in the outlet Z
1
increases till the effort of
pressing on the lever 1 gets balanced by the force created by the pressure acting on the upper pis-
ton 25. Thus, the follow-up action in the brake valve upper section is carried out.
At the same time with the pressure increase in output Z
1
, the compressed air via opening
«
а
» gets to the cavity above the big piston 23 of the brake valve lower section. Lowering down,
the big piston closes the outlet of the valve 17 and separates it from the seat in the lower part 15.
The compressed air from the outlet V
2
goes to the outlet Z
2
and further to the operation units of
the second circuit of the service brake.
At the same time with the pressure increase in output Z
2
, the pressure under pistons 14
and 23 rises, as a result of which the force acting on piston 23 from above, gets balanced. Owing
to this, the pressure is set in the outlet Z
2,
corresponding to the effort on the brake valve lever.
Thus, the follow-up action in the brake valve lower section is carried out.
At the brake valve lower section failure, the upper section operates as described above.
Two-section brake valve maintenance consists in its periodical inspection, cleaning from
dirt, checking for tightness.
Pay attention to the condition of the protective rubber boot of the valve and to its tight
fitting to the housing, because dirt on the pusher and friction surfaces of the valve causes the
brake valve failure.
The brake valve tightness is checked by means of the soapy emulsion in two positions:
breaks applied and brakes released. Air leakage through the atmospheric output of the brake valve
when the brakes are released indicates that the inlet valve of one of the sections is non-tight, and
the air leakage when the brakes are applied indicates that the outlet valve of one of the sections of
the brake valve is non-tight. Replace the brake valve in case of leakages.
5.5.2.5 The Four Circuit Brake Valve (Fig. 89) is intended to divide one supply line in-
to two main and two additional circuits; to cut off the circuit automatically in case of its damaging
or untightness; to keep the reserve of compressed air in the undamaged circuits; to keep the com-
pressed air in all circuits in case the supply line is damaged.
Compressed air supplied to the outlet I, goes through “a” and “d” throttle openings,
opens return valve 15 and comes to the circuit outlets II, III and two additional circuits through
“b” and “c” side openings in the valves 3,13.
Initially, the pressure in the circuits increases slowly as air passes throttle and side open-
ings slowly. Having passed the throttle openings, air presses on diaphragms 4,12 and overcoming
spring 6,10 force air opens valves 3 and 13 at full extent. The pressure in outlets II and III be-
comes equal to the outlet I pressure.
Throttle openings in valves 3 and 13 ensure brake drive circuits filing up with air at a
very small pressure in outlet I.
