Checking and adjusting the pneumat-
ic system brake valve and its actua-
tor.
The pneumatic actuator of the trailer
brakes is provided with a brake valve.
For normal operation of the brake valve
and brakes of trailers unitized with a
tractor, check the brake valve operation
and, if necessary, adjust it.
The adjustments shall be performed at
a free position of the tractor brake con-
trols after adjustment of the working and
parking brakes.
For a single-line pneumatic actuator:
1. Attach a pressure gauge with the
scale of at least 10 kgf/cm
2
to the
connection head of the tractor pneu-
matic drive.
2. Turn the compressor on and pressur-
ize the air bottle to the value of 7.7-
8.0 kgf/cm
2
against air pressure indi-
cator located on the tractor dash-
board. The pressure gauge attached
to the connection head shall display
at least 7.7 kgf/cm
2
. If it is below the
given value, proceed as follows:
• Check the presence of the gap “a”
between the pin (5) and the upper
edge of the slots of the levers (7 and
8). The gap shall be 1-2 mm;
• If there is no gap, unsplint and re-
move the pin (5) and adjust the rod
length by rotating the rod end (4).
3. Check and adjust, if necessary, the
preliminary compression of the spring
(3) to the size of 36-38 mm by rotat-
ing the nuts (2), after which lock the
nuts.
The preliminary compression of the
spring is adjusted so that when step-
ping on the service brake pedal or
applying the parking brake, first the
brake valve plunger would move to
the stop and then the spring would be
compressed.
4. If necessary, adjust the brake valve.
The pressure in the pneumatic line,
i.e., pressure on the gauge attached
to the connection head, is adjusted
by rotating the nut located under a
rubber boot (8).
To perform the adjustment, discon-
nect the rod (1) from the lug (9), re-
move the boot (8), unscrew the lug
by 2-3 turns and adjust the air pres-
sure to minimum 7.7 kgf/cm
2
(for
Hungary and Germany – 5.3-6.0
kgf/cm
2
) by turning the nut. Screw
the lug into the nut to the stop and
lock it. Put on the boot and attach
the rod.
If the brake valve actuator and the
valve are adjusted properly, when
moving the blocked brake pedals to
the full travel or applying the parking
brake to fixation at the 2
nd
or 4
th
tooth, the pressure as indicated by
the pressure gauge attached to the
connection head shall decrease to
zero.
Disconnect the pressure gauge from
the connection head.
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