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6.3
Depressurised systems
Depressurised systems (Fig. 11 and Fig. 12) have a negative fuel
pressure (depression) on intake to the burner.
Usually the tank is lower than the burner.
SYSTEM ONLY FOR ITALY:
Automatic shutoff device as per Ministry of Internal Affairs' regu-
lation no. 73 dated 7/29/71.
The installer must ensure that the supply de-
pression is not above 0.4 bar (30 cm Hg).
Above that level, gas leaks out from the fuel.
WARNING
The pipes must all be perfectly sealed.
20013962
Hydraulic system
H
meters
0
0,5
1
1.5
2
3
D9550
3.5
H
= difference of level;
L
= max. length of the suction pipe;
Ø i
= internal diameter of the oil pipe.
In the systems in Fig. 11 and Fig. 12, the table shows the maxi-
mum indicated lengths for the supply line, depending on the dif-
ference in level, length and the diameter of the oil pipes.
Fig. 11
6.3.1
Pump priming
On the systems in Fig. 11 and Fig. 12 it is necessary to start the
burner and wait for the priming.
Should lockout occur prior to the arrival of the fuel, await at least
20 seconds before repeating the operation.
In two pipe vacuum systems (Fig. 12) the return line should ter-
minate within the oil tank at the same level as the suction line. In
this case a non-return valve is not required.
D9551
Should however the return line arrive over the fuel level, a non-
return valve is required.
This solution however is less safe than previous one, due to the
possibility of leakage of the valve.
Fig. 12
14
GB
L meters
Øi
Øi
8 mm
10 mm
35
100
30
100
25
100
20
90
15
70
8
30
6
20
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