Preferred FlexFit 110 - Field Selectable Flex Sequence Option; Servo Checks; Automatic Fuel SSOV Leak Test; Lockout and Alarm History

Description – Features 1-3
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
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Field Selectable Flex Sequence Option
The ex sequence is an optional set of parameters that gives the commissioning engineer more exibility and options related
to burner ignition and gas valve leak testing. When the "Flex Sequence Option" is enabled, the various pilot ame and main ame
timings and whether direct spark ignition is used are set by the subsequent parameters. If the "Flex Sequence Option" is disabled,
the default timing sequence will be used. For more information, see "Flame Safety > Flex Sequences" on page 4-62. The "Flex
Sequence Option" must also be enabled if gas valve leak testing is to be used.
Servo Checks
Servos are stroke tested from minimum to maximum position during every burner startup. A detailed message will be displayed
to facilitate servo troubleshooting. Parameter "P2.5.6 FGR Servo Check Mode" on page 4-70 allows the setup engineer to choose
the desired action of the FGR damper servo during the servo test – "Closed Then Open" or "Open Then Closed".
Automatic Fuel SSOV Leak Test
Safety shutoff valve leak testing can be performed automatically. See "Gas Valve Leak Test Option" on page 4-64 for more
information.
Lockout and Alarm History
The LCD display has a large historical memory that stores the most recent 10 lockouts with a snapshot of boiler/burner variables
at the time of each lockout.
MAF and PAF Safe Start Checks
Unless the FD Fan is in running manually (in hand), the non-recycling and purge interlock inputs must be deenergized at the start
of a cycle, indicating that these switches are operable and not bypassed. There is a nuisance delay timer of 60 seconds before a lockout.
High Flue Gas Temperature Shutdown
The FlexFit can monitor ue gas temperature, and if it exceeds a user-dened setpoint (see parameter "P1.2.5 Lockout SP, Flue
Temp" on page 4-62), the FlexFit initiates a trip. This serves as additional protection against ring a "dry" boiler.
Fuel Selection and Flexibility
The desired fuel is selectable via eld contact inputs. The burner will light-off only if a single fuel is requested. If the requested
fuel is changed when not in standby or lockout, the burner will lockout.
Any two of light oil, heavy oil, natural gas, waste gas, propane, and/or renewable fuel ring are supported by the FlexFit. Fuel
ring exibility offers the opportunity to save fuel cost by ring the fuel that is most economical. The FlexFit will use the appropriate
combustion curve for the selected fuel.
FD VSD to VSD Bypass Changeover
There are two separate combustion curves for forced draft fan operation – Variable Speed Drive (FD VSD) and xed speed
(VSD bypass or xed-speed fan). The operator shuts down the burner, selects FD VSD or VSD bypass via the VSD controller, and
restarts the burner. The FlexFit will use the appropriate combustion curve for the selected mode of operation. Two sets of fuel/air
ratio curves can be stored for each fuel. If using only a xed-speed fan, then only one set of curves is necessary.
Pilot Test Hold
Pilot test hold can be turned on before the pilot ame has been proven so a pilot turndown test can be performed. See section
"Pilot Test Hold" on page 3-51 for more information.
Flame Scanner/Relay
The FlexFit can be congured for multiple styles of scanner/relays, including UV, UV self-checking, and IR. The scanner/relay
must be a listed device and have a dry contact 120 VAC ame-on/ame-off output. The FlexFit provides a power supply and the
analog inputs for the ame intensity relay display. Preferred Instruments ame scanners are intended for monitoring all gas, oil, and
waste gas red burners. All essential circuits are supervised. Two LEDs indicate scanner status.
Fuel/Air Position "Pacing Logic"
The key to efcient boiler operation is accurate, repeatable positioning of the fuel and air servos and VSDs. When the ring
rate is changing, the FlexFit moves all servos and VSDs simultaneously. However, because different servos can move at different
rates, the FlexFit ensures all servos and VSDs move at the same rate. Twice per second, the FlexFit measures the current position
of each servo and VSD, calculates a new target position/speed for each servo and VSD, based on the curves, and moves all outputs
simultaneously. This feedback measurement compensates for output position or speed deviations. When the fuel valve is not changing,
all outputs (servos and VSDs) will settle at each output's curve value.