Roberts Gorden MGB Series Manual de servicio descargar pdf (Pagina 48)

COMBAT

CABINET HEATERS INSTALLATION, COMMISSIONING, OPERATION AND SERVICE MANUAL

42 of 85

10.2.1 Fire the Burner for Dungs Combination

Gas Valves

1. Open the gas isolating valve.

2. Connect a suitable pressure gauge to the

burner pressure test point.

3. Reset the lockout button of the control box and

the burner should now fire. If lockout should

occur when the main gas valve energises,

repeat 3 or 4 times. If after several attempts the

burner does not fire, then turn the main gas

governor adjusting screw 3 turns clockwise.

See Page 41, Section 10.2 and repeat until the

burner fires.

10.2.2 Set Gas Rate

1. S witch on again and allow the burner to fire and

to settle for a few minutes.

2. Adjust the main gas burner pressure to the

value given in the relevant Data Table for the

model concerned using the Main Gas Regula-

tor (accessed under the swivel cover).

The results of setting the gas flow rate by using

burner pressure only can lead to quite wide

variations in heat input due to the nature of the

burners used.

NOTE: If the correct burner pressure cannot be

reached, then check the inlet pressure to the valve,

with the burner firing. See Technical Data Tables on

Page 11, Section 4.5 for inlet pressure

requirements.

Do not continue to adjust the regulator if the

pressure is not changing.

If the inlet pressure is too low to allow the correct

burner pressure setting, then the gas inlet pressure

must be corrected before completing the

commissioning.

10.2.3 Check Gas Rate

It is important to check that the gas rate set during

the commissioning is within ± 5% of the requ

ired

flow rate.

This may be achieved by checking the gas flow to

the heater wherever possible by using the gas meter

and timing the flow through the meter. The results

should be compared with the requ ired flow rate for

the model given in the Data Tables, adjusting the

burner pressure to correct for any error. Checking

the gas rate must be carried out with all other

appliances including any pilots, turned off.

1. A ft e r b urner pressure adjustment, allow the

heater to operate for at least 15 minutes and

then re-check settings.

2. Remove the manometer and refit all covers to

the valve and tighten the screw of the outlet

pressure tap.

3. Check gas flow rate at gas meter.

10.2.4 Control - Gas-Fired Heaters

Refer to the burner manufacturers instructions for

further detail. Gas bu

rners have two pressure

switches, one is configured to cover combustion air

and reaction to increases in combustion chamber

pressures. The second pressure switch is used for

monitoring the incoming gas supply pressure.

NOTE: The low gas pressure switch should be set at

50% of the recorded inlet working gas pressure.

10.2.5 Description of Gas-Fired Heater Control

The gas-fired burner fitted to all cabinet heaters is

controlled by a full sequence plug-in control. This

control ensures the safe start and stop sequence

and also monitors the safe presence of a flame and

burner air pressure.

10.2.6 Sequence of Operation - Single 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 t

urns 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-

ously 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.

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Roberts Gorden MGB Series Manual de servicio Pagina 48

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