Retractable Tag Axle (Optional); Preheating System - PREVOST H3-41 Manual

RETRACTABLE TAG AXLE
Operation of the tag axle is controlled by a valve
located on the right lateral console. The valve can
be switched to either the WHEELS UP or
WHEELS DOWN position.
automatically raised or lowered by air pressure
according to the valve position. Refer to "Controls
& Instruments" section.
The tag axle service brakes and parking brakes
operate only when the tag axle is in the WHEELS
DOWN position. Never lower the tag axle while
the coach is moving. When the tag axle is in the
WHEELS UP position, the corresponding indicator
light will illuminate, and a beep will sound to alert
the driver to the tag axle position. The tag axle
can be raised in tight manoeuvring areas like in a
parking lot or to make it easier to turn a short
corner. The tag axle shortens the wheelbase and
allows tighter turning.
transfers extra weight and additional traction to
the drive wheel providing improved control on
slippery roads.
CAUTION: ALWAYS RAISE THE TAG AXLE
BEFORE RAISING THE COACH TO PREVENT
DAMAGE TO THE SUSPENSION.
CAUTION: NEVER LOWER THE TAG AXLE
WHILE COACH IS MOVING.
TAG LOAD REALEASE SYSTEM (TLR)
This standard system allows automatic unloading
of the tag axle air springs, without raising the axle,
whenever coach speed drops to less than 8 mph
(13 km/h) and steer angle exceeds 22.5° (1 1/4
turns of the steering wheel). The system transfer
automatically the tag axle load to the drive axle.
It reduces tag wheel shearing to convey shorter
turning radius for tighter cornering and remarkable
agility in close-quarter manoeuvring, whether
backing up or moving forward.
The axle will be
Raising the tag axle

PREHEATING SYSTEM

The auxiliary preheating system is used for
preheating and retaining the heat of water-cooled
engines. It can be used before starting the engine
to facilitate starting and to provide rapid operation
of the interior heating system. It can also be used
during engine running to maintain coolant heat
and to maintain the interior heating temperature.
Refer to "Controls & Instruments" section under
"Water Heater Timer" of the "L.H. Control Panel".
The heater operates independently of the engine.
It is connected to the cooling system, heating
circuits, and to the coach fuel and electrical
system.
Switching On the Heater
The pilot lamp turns on when the heater is
switched on. Combustion air flows in to flush out
the combustion
circulation pump begins operating.
metering pump delivers fuel in precise amounts to
the combustion
combustion air form a combustible mixture which
is ignited by the glow plug.
Once the flame sensor has signalled to the control
unit that combustion has taken place, the glow
plug and ignition coil are switched off.
The hot combustion gas is diverted at the end of
the flame pipe.
through the indirect heating surfaces of the heat
exchanger. The heat exchanger transfers the
heat to the water passing through the heat
exchanger.
The heater is thermostatically controlled and
operates intermittently (i.e., the switched-on time
of the burner varies depending on the heat
requirement). The water temperature is controlled
by the setting of the built-in water thermostat.
The water circulation pump remains in operation
as long as the heater is operating; even during
the regulated intervals and during the delayed cut-
out of the switched-off heater. The pump can also
be operated independently of the heater by means
of an appropriate circuit.
switched on at any time (i.e., during the delayed
cut-out period).
delayed cut-out time expires.
4-9
OTHER FEATURES
chamber, and the
The fuel
chamber, where fuel
The hot gas is then forced
The heater can be
Ignition takes place after the
water
and