Roberts Gorden MGB Series Wartungshandbuch PDF herunterladen (Seite 50)

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CABINET HEATERS INSTALLATION, COMMISSIONING, OPERATION AND SERVICE MANUAL

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control ensures the safe start and stop sequence

and also monitors the safe presence of a flame and

burner air pressure.

10.3.5 Sequence of Operation - Two-Stage

Burner

1. With the external controls on calling for heat,

and the pressure switch at rest, the burner fan

will switch on after the control does a "self

check".

NOTE: If the pressure switch contacts (normally

closed) are open, the heater will not start.

2. The combustion air fan turns on and the pres-

sure switch contacts close within the next 5

seconds to indicate sufficient combustion air or

lockout will occur.

3. The sequence continues with a purge period

with the burner fan running.

4. The electrical ignition switches ON at the end of

the purge period.

5. The main gas valve opens and once a flame

has been established, this remains open until

close down. The flame probe is now continu-

sly monitoring for the safe presence of flame.

6. Three seconds later, the electric ignition turns

off, leaving the gas flame to be proved as sta-

ble.

7. The control is now in its normal run position.

8. If the flue becomes blocked during the units

operation, the unit will deactivate and the lock-

out indicator light will activate.

After setting the minimum burner input and

combustion, the following check must be made:

Run the heater on low fire for a minimum of 15

minutes. Check the flue gas temperature. If the flue

gas temperature falls below 125° C, increase the low

fire gas setting until the temperature reaches 125° C,

otherwise condensation may form.

10.4 Motor Starter and Thermal Overload

On belt-driven models, the motor is controlled by a

direct on-line contactor starter fitted with thermal

overload protection. If the thermal overload

operates, the main fan will not run. To reset, press

the reset button on the o

verload unit.

NOTE: For models with a 5.5 kW motor or larger, the

direct on-line starter will be replaced by an

automatic starter.

The overload should be set to indicate

approximately 0.2 A above the normal running

current of the heater. See Page 11, Section 4.4.

10.4.1 Burners

For details of the packaged burners, see the

manufacturer's instructions and Page 11, Section

4.5 through Page 14, Section 4.8. When reading the

data tables, ensure that the correct table for the

burner and gas valve installed is being used. The

data tables are listed under a burner reference letter

which can be found on the heater data plate.

10.5 Gas Valves

Dungs Combination Gas Valve

All model 015 - 030 gas-fired burners operate as

direct main flame ignition and have no separate start

gas train. All other models operate with a first stage

start gas flame supplied from a start gas train

containing a start gas pressure regulator and two

safety shut-off valves, for all gas types.

The main gas is released at the second stage, and

the combination main gas valv

e block contains a

main burner pressure regulator and two safety

shutoff valves, for all gas types. See Page 44, Figure

19. Please refer to the manufacturer's instructions

for setting the controls.

Figure 19: Gas Train Circuit for Dungs Gas Valves (all models)

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