Air System; Brakes; Air Reservoirs; Optional Wet Tank Automatic Drain Valve - PREVOST H3-41 Maintenance Manual

SECTION 12: BRAKE AND AIR SYSTEM

2. AIR SYSTEM

The basic air system consists of an air
compressor, reservoirs,
interconnecting lines and hoses. It provides a
means for breaking, operating controls and
accessories and suspension (refer to Section 16,
"Suspension", for complete information on
suspension description and maintenance). An
air system schematic diagram is annexed in the
technical publications box provided with the
vehicle for better understanding of the system.

3. BRAKES

This vehicle uses both the service brake and
emergency/parking brake. The service brake air
system is divided into two independent circuits to
isolate front brakes from rear brakes, thus
providing safe braking in the event that one
circuit fails. Front axle brakes operate from the
secondary air system, while brakes on both the
drive axle and tag axle operate from the primary
air system.
NOTE
The tag axle service brake operates only when
the axle is in normal ride position (loaded and
down).
Furthermore, the brake application or release,
which is speed up by pneumatic relay valves (R-
14), will start with the rear axles and will be
followed by the front axle, thus providing uniform
braking on a slippery road. The vehicle is also
equipped with an Anti-Lock Braking System
(ABS), which is detailed later in this section.
The drive is provided
emergency/parking brakes, which are applied
automatically whenever the control valve supply
pressure drops below 60 psi (413 kPa). The
optional emergency/parking
system allows the driver to release spring
brakes, and to move the vehicle to a safe
parking place, such as in the case of a self-
application of these brakes due to a drop in air
pressure.
8 PA1621 Maintenance Manual All Series | Revised June 2020
valves, filters and
with spring-loaded
brake overrule

4. AIR RESERVOIRS

The air coming from the air dryer is first
forwarded to the wet air tank, then to the primary
(for the primary brake system), secondary (for
the secondary brake system), and accessory (for
the pneumatic accessories) air tanks (Figure 2
and Figure 3).
Additional air reservoirs may be installed on the
vehicle: the kneeling air tank, emergency/
parking brake overrule air tank and I-Shift
transmission air tanks.
4.1 OPTIONAL WET TANK AUTOMATIC
DRAIN VALVE
The optional wet tank automatic drain valve
(Figure 1) is designed to remove liquids from the
wet tank each time the brake is applied as the
solenoid is connected to the stop light circuit. A
built-in heater prevents freeze-ups and keeps
the air system clean in all temperature.
4.1.1

Installation

1. Make sure that there is no pressure in the
wet tank (emptied tank).
2. Fit the automatic drain valve to the wet tank.
Tighten valve finger tight and then tighten an
additional 1 ½ turns, do not over tighten.
3. Connect the power cable to the valve
connector.
4. Charge the air system and make sure there
is no leakage. Also check functioning of the
drain valve by applying the service brake.
FIGURE 1: WET TANK AUTOMATIC DRAIN VALVE