Navien LCB700-21RS Installation & Operation Manual page 31

Double Pipe Sub-Gravity Feed System
With the storage tank outlet below the burner, a two pipe system should be used. The return pipe should be at the same level in the tank
as the supply pipe, both being 75 to 100 mm above the base of the tank. The pipe ends should be a sufficient distance apart so as to
prevent any sediment from being disturbed by the return entering the supply pipe.
Make sure that the bottom of the tank is more than 3.5 m below the burner.
A non-return valve should be fitted in the supply pipe together with the filter and fire valve. A non-return valve should be fitted in the
return pipe if the top of the tank is above the burner.
The pump vacuum should not exceed 0.4 bar. Beyond this limit gas is released from the oil.
For guidance on the installation of top outlet fuel tanks and suction oil supply sizing, see OFTEC technical book 3.
Oil
Pump
Boiler
Head
0 m
-0.5 m
-1.0 m
-1.5 m
-2.0 m
-2.5 m
-3.0 m
-3.5 m
Min. 1 m
Φ10
50 m
45 m
40 m
30 m
25 m
20 m
15 m
10 m
Non-
Return
Valve
Oil
Storage Tank
Oil Strainer and
Water Separator
Oil
Filter
Max. Oil Pipe Length
Φ12
100 m
30 m
95 m
80 m
65 m
50 m
35 m
20 m
Connecting the Oil Supply 31