MODULATING CONTROLS
Controller
The standard method of operation is based on the Landis & Staefa RWF40 Universal Controller,
which has been designed for use on gas fired installation, where it provides temperature or pressure
control of modulating burners with continuously adjustable fuel throughput.
The control output of the RWF40 is a potential free 3-position switch, which is used for the control of
reversible motors. The control signals for the open (Y1) and closed (Y2) are indicated on the
controller face by light emitting diodes.
When the boiler control calls for heat, the modulating servomotor will travel to the high flame position
and interlock the control circuit. An air pre-purge will take place at this position for a predetermined
period, at the end of which the burner sequence controller will stop until the modulating servomotor
has travelled to the low flame position and interlocked the control circuit again. The sequence
controller will now recommence its operational cycle and the burner will light and remain at low flame
until the high flame release signal is given by the sequence controller.
The modulating servomotor will now move to high flame and remain at this position until the desired
boiler temperature/pressure is attained. From this stage the modulating unit will commence to move
towards the low flame position but, depending on the temperature/pressure, will stop in any
intermediate position between low and high flame.
Commissioning Controls
Two switches, Hand/Auto and Inching, are included in the burner panel. In auto mode the burner will
respond to the demand of the boiler via the RWF40 modulating controller. In Hand mode the RWF40
controller is disconnected from the burner modulating servo. This servo can now be ‘inched’ towards
high or low flame by operating the 3-position bias inching switch, thus allowing combustion settings to
be made at these points. Whilst in Hand mode, care must be exercised when the burner is in a high
firing range so that the boiler demand is not exceeded. It is imperative that the burner control circuit
operating and limiting instruments are fitted and functioning correctly.
Temperature Detector
The immersion temperature detector type QAE20.1 is used in all hot water boiler applications. The
detector has a plastic casing to IP42 with a snap-on cover and an immersion stem. The connection
terminals can be accessed after removal of the cover. Cable entry is made via a cable entry gland.
In all applications an immersion pocket with a flat seal is supplied.
The detector should be installed in an elbow such that the pocket points against the direction of flow.
With all detector versions, the immersion length must be a minimum of 60mm.
Pressure Detector
The pressure detector type QBE620 is used in all steam boiler applications. The detector has a
plastic casing to IP42. It is necessary to mount the water trap pipe supplied.
General
The detector must not be covered by lagging.
Mounting instructions are printed on the packing.
MDFL 3300 & MDFL 4000 Issue 2 08/08
Page 23
Summary of Contents for MDFL 3300
Page 16: ...MDFL 3300 MDFL 4000 Issue 2 08 08 Page 15 VALVE PROVING SYSTEM LDU 11 Standard fitting...
Page 30: ...MDFL 3300 MDFL 4000 Issue 2 08 08 Page 29 MODULATING CAM BOX...
Page 43: ...Electrode Setting Details MDFL 3300 MDFL 4000 Issue 2 08 08 Page 42 All dimensions in mm...
Page 48: ...NOTES MDFL 3300 MDFL 4000 Issue 2 08 08 Page 47...
