Webasto Thermo Top Z Shop Manual page 35

Thermo Top E and Z/C
8.6.2 Connection to Vehicle Fuel System
In vehicles with carburettor or fuel injection including a
return line the heater fuel system integration must be
according to Fig. 802.
Carburettor engines without return line must have the
heater integrated in the fuel system's fuel supply line
between fuel tank and vehicle fuel pump.
NOTE
A fuel supply line can normally be identified by the
installation of a fuel filter. If the degassing vessel is
included in the vehicle fuel system installation, the fuel tap
must be located upstream of the degassing vessel.
The following table lists the pressures permitted at the fuel
tapping location.
Permitted fuel feed
height (H) m
0.00
1.00
Permitted suction
height S (m)
0.00
0.50
1.00
Fuel tappings from the supply or return line may only use
the special Webasto fuel tap.
Fig. 804 Webasto Fuel Tap
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at max. permissible
overpressure (bar) in fuel line
–0.20
–0.11
at max. permissible negative
pressure (bar) in fuel tank
– 0.10
– 0.06
– 0.02
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The fuel tap is to be mounted so that air or gas bubbles
may escape towards the fuel tank.
Air or gas bubbles may build up in the vehicle fuel line
in case the carburettor or the fuel pump is leaking or if
ambient temperatures exceed the fuel evaporation
temperature.
The fuel tap should not be located near the engine, as gas
bubbles may build up due to the heat radiated by the
engine resulting in malfunctions of combustion operation.
When installing the heater in vehicles with fuel injection
system, the fuel pump location, internal or external of the
fuel tank, must be investigated.
With a fuel pump located inside the fuel tank, fuel may be
tapped only from the return line, ensuring that the return
line is routed almost all the way down to the fuel tank floor.
Otherwise the return line may be lengthened.
If the fuel return line is provided with a check valve, a
bypass must be provided.
With a fuel pump located outside of the fuel tank the fuel
tap may be located between tank and fuel pump.
8.6.2.1 Fuel Lines
Fuel lines may only be steel, copper, or plastic lines made
of unhardened, light and temperature stabilised PA 11 or
PA 12 (e.g. Mecanyl RWTL) according to DIN 73378.
As in most cases a permanently rising fuel line routing
cannot be ensured, the inner diameter must not exceed a
certain value. Starting from an inside diameter of 4 mm,
air or gas bubbles accumulate resulting in malfunctions
should the lines be descending or having sags. The
diameters specified in Fig. 803 ensure no disturbing
formation of bubbles.
A descending line routing from the dosing pump to the
heater should be avoided.
Loose fuel lines must be secured in order to avoid
sagging. The installation must ensure protection against
stone impacts and undue temperatures (exhaust line).
Hose clamps must be torque tightened to 1.0 + 0.4 Nm.
8 Servicing
NOTE
NOTE
803