Riello DB 4 SM CO1 A0 FS1 T150 Installation, Use And Maintenance Instructions page 37

5.3 Servomotor adjustment
1 - 4 : Limit switch cam (max. air damper opening)
2 : Limit switch cam (air damper closed)
3 - 5 : Minimum delivery (and ignition) position cam
6 : Positioning reading indicator
7 : Servomotor release
The servomotor contemporarily regulates, by transmission, air delivery
and pressure and delivery of the fuel being used.
It is fitted with a number of adjustable cams that action the same
number of selector switches.
Cam pos.1: limits maximum opening of the servomotor.
Cam pos.2: limits servomotor limit switch in the 0° position.
When the burner is off, the air damper is completely
closed.
Cam pos.3: fixes the minimum modulation position.
It is set in the factory at approx. 20° (just one type of fuel).
Cam pos.4: limits maximum opening of the servomotor (for mixed burners working with gas).
Cam pos.5: limits minimum delivery. It is set in the factory at approx. 20° (for mixed burners working with gas).
Cam rest: available.
Important: the position of 130° must not be exceeded for limit switches (cam 1 - 4).
5.4 Air/fuel adjustment
Fuel/combustion air is synchronized by means of a servomotor that, connected to a variable-profile cam, operates the outlet air
dampers and, by means of suitable linkage, the combustion head and gas butterfly valve.
To reduce pressure loss and to have a wider adjustment range, it is best to set the servomotor to the maximum output used, as
near to maximum opening (130°) as possible.
On the gas butterfly valve, the fuel's partial setting adjustment based on required output, with the servomotor fully open, is made
by using the pressure stabilizer on the train.
When setting the air/fuel ratio for the gas burners, the air and gas variable profile cams must be used, Fig. 22.
Fig. 22
CHAPTER
1 2
3
4
D1499
5
Preparation for start up
1 Cam
2 Adjustment screws
3 Fixing screws
4 Variable profile
D1500
Fig. 21
15