Brake System

Page 33

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Volvo Bus Service and Maintenance Manual

 Air dryer
60 Disassemble and clean the air dryer. Change the desiccant (twin-tower type change interval 24 months).
 Line filter in brake system (water separator)
 (B10M without air dryer)
61 Depressurize the brake system. Disassemble and blow clean the filter.
 Anti-icing reservoir (buses without air dryer)
62 If necessary top-up the reservoir to 2/3 with anti-icing fluid.
 Load-sensing valve
63 Check that the ventilation hole in the cap is not blocked (concerns early prod. valve 475 700...).

Air dryer

WARNING! The compressed-air system must be pressureless before disassembling is commenced. Over and above draining the wet tank, the air dryer feed line should also be slackened to evacuate any pressure in the air dryer.

If the desiccant contains oil, the air compressor must be overhauled or replaced. Oil impairs the desiccant so that it cannot absorb the moisture. Replace the desiccant when cleaning the air dryer. If possible, do this in the summer, about three months before the cold weather sets in.

Note that all desiccant in the replacement package must be packed into the container. Not enough granules in the container will cause them to shake loose and perhaps break up and thereby lose their absorbing capacity.

Also check that the heating element in the bottom of the air dryer is functioning. The single tower type dryer has an output of approx. 60 W and the twin-tower type approx. 100 W.

It should engage automatically below approx. +10°C and cut-out above approx. +30°C.

Air dryer, twin tower type
Air dryer, twin-tower type, desiccant container (d)
Air dryer, single-tower type, filling with desiccant
Air dryer, single-tower type, filling with desiccant

Anti-icing reservoir

At increased engine speed, air bubbles should flow through the fluid when the air compressor charges.

Load-sensing valve

Pressure in kgf/cm2 at 6 kgf/cm2 ingoing brake pressure.
Wabco no.Bellows
Outgoing brake
Volvo P/N
475 700 25103.3 to 6.04.0 to 6.0 
475 700 24600.6 to 4.23.8 to 6.01191569
75 700 14102.0 to 4.84.2 to 6.0 
75 711018/0382.8 to 6.85.0 to 6.03031393
475 711 019/0391.8 to 5.24.8 to 6.03031392
475 711 020/0401.2 to 4.84.0 to 6.03031391

Concerning the load-sensing valve for the B6FA, refer to separate instructions.

Load sensing valves