Description – Combustion Control System 1-9
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
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CC
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Gas Valve Leak Test Option (Flex Sequence Option Only)
If enabled, when possible, the leak test is performed after the completion of post purge. If the recycling or non-recycling trips
open during the leak test, the leak test is postponed and done during the next start-up, after prestart and before purge. Optionally, the
leak test can be performed both after post purge and pre-purge. See "Gas Valve Leak Test Option" on page 4-64 for more information.
Lockout
The FlexFit reverts to the lockout state whenever an unsafe or undesirable condition has been detected. The operator must
reset the FlexFit before a burner restart can be attempted. Refer to the "Section 5 – Troubleshooting" for an overview of the lockout
messages and their meanings.
Interlock Groups
Call for Heat
Call for heat means a burner start request has been made by a local source, a remote source (T17 or Modbus), or a setpoint
deviation.
Recycling Limits
Should the recycle limit circuit open at any time during a normal sequence, the FlexFit will conduct a shutdown and revert to
the standby state. The burner will automatically restart when the recycle limit closes.
Fuel Select
Changing the fuel selection should only occur when the burner is in standby or lockout (recycle limits are not made). If there
is a problem with the selected fuel (selected fuel changes during operation, both fuels are selected, or neither fuel is selected), the
burner will lockout.
Non-Recycling Limits
Should the non-recycle limit circuit open from the end of prestart to the start of post purge, a lockout will result.
Purging
Purging indicates that the purge/high re limits are made. Should the purge limit circuit open for longer than 30 seconds (cumu-
lative) during purge, the FlexFit will lockout.
Ignition
Ignition indicates that the low re start interlock is made and, if necessary, the draft damper is open. The FlexFit will not attempt
to light a ame until the ignition interlock is made.
False Flame
If a ame is detected during the standby, safe start, prestart, or purge states a lockout will result. A false ame is ignored for
120 seconds after the fuel valves close and for the rst 30 seconds during prestart.
Flame Failure
A lockout occurs if no ame is detected during PTFI, MTFI, release to modulate, or ALFCO.
Fuel Valve Proof of Closure Switches (POCS)
The POCS indicate to the BMS that the fuel valves are closed. If they are shut during MTFI, release to modulate, or ALFCO or
open at other times, a lockout will occur. If allowed by code, POCS can be disabled for smaller burners.
Fan Speed
If the operator changes the xed fan speed versus variable fan speed input T26 in any of the FlexFit states (except standby or
lockout), the burner will lockout.
Combustion Control System
The primary objective of a combustion control system (CCS) is to ensure that the fuel/air ratio of the burner is maintained at
the commissioned levels. This is accomplished by maintaining all servos, VSDs, control valves, and air dampers at predetermined
positions based on curves set up during commissioning – a control type called parallel positioning.
The secondary objective of a CCS is to modulate the ring rate to provide a continuous supply of steam or hot water at the
desired pressure or temperature. Based on PID control action or a remote ring rate demand signal, the FlexFit-CC can modulate
the burner to maintain the process variable at a predetermined setpoint.
Other FlexFit options available, that can be used to enhance the performance of the CCS, are as follows:
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