Midco Unipower G-Series User Manual
Page 14
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Unipower burners may feature a redundant solenoid gas safety valve. This valve is an On-Off (2
position) valve.
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When the valve operator is electrically energized, a plunger lifts the valve disk off the valve seat,
allowing gas to flow. When the current is broken the valve closes. It will normally require no service. If
the operator malfunctions or the valve leaks replace the entire valve. After replacement check for
l e a k a g e .
WARNING: Explosion hazard. Do not use this device if it gets wet. It can malfunction and
cause serious injury or death. Replace any device that has been wet.
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Standard Unipower G-Series burners are equipped with a Honeywell RM7895 microprocessor based
burner control, employing a flame rectification system of flame detection. Burner construction for special
codes and/or insurance requirements such as Factory Mutual or Industrial Risk Insurers (IRI) may require
alternate controls. Refer to Section XIV Special Equipment. A safe start and run control sequence is
provided with instantaneous response to presence or loss of flame signal. Flame failure response time is
3 seconds. Pilot Flame Establishing Period (PFEP) is field selectable from 4 or 10-seconds. The RM7895
features a pre-purge time (30-seconds for On-Off, 90-seconds for 2-Step or Modulating burners) and a
plug-in amplifier. An airflow circuit is also field selectable to allow either lockout or recycle upon loss of
airflow. Five LED's (light emitting diodes) are provided to display sequence information. Refer to the
Honeywell RM7895 literature for detailed operating information, configuration requirements, testing
and service.
INITIATE ("POWER" LED is lit).
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The RM7895 enters the I N I T I A T E sequence when it is powered. The I N I T I A T E sequence lasts for ten
seconds unless the voltage or frequency tolerances are not met (refer to Honeywell RM7895 literature
for criteria). When tolerances are met, the I N I T I A T E sequence will restart. If the condition is not
corrected and the hold condition exists for four minutes, the RM7895 will lock-out. Causes for hold
conditions in the I N I T I A T E sequence are in the Honeywell RM7895 literature.
STANDBY ("POWER" LED is lit).
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The RM7895 is idle in this state of sequencing. When the burner switch, limits, operating limit
controls and all microprocessor monitored circuits are in the correct state for the RM7895 to continue,
sequencing will advance to P R E P U R G E.
PREPURGE ("POWER" LED is lit).
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The RM7895 in this application features a prepurge time of 30-seconds for On-Off, 90-seconds for 2-
Step or Modulating burners.
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Once the S T A N D B Y sequence has a "CALL FOR HEAT" input, normal start-up prepurge will be
i n i t i a t e d .
A .
The blower motor is powered to start the prepurge sequence.
B .
The airflow interlock switch must close in ten seconds of prepurge or within the
specified purge card timing. Otherwise a recycle to the beginning of prepurge or
lockout will occur, depending on how the airflow switch selectable jumper is
configured. Refer to Honeywell RM7895 literature for configuration requirements.
IGNITION TRIAL
1 .
PILOT FLAME ESTABLISHING PERIOD (PFEP)
A .
The pilot valve and spark generator are energized.
B .
Flame must be proven by the end of the 4 or 10-second PFEP to allow the sequence to
continue. If flame is not proven by the end of PFEP, a safety shutdown occurs.
2 .
MAIN FLAME ESTABLISHING PERIOD (MFEP)
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After the ignition trials, and with the presence of flame, the main valve is energized.
("MAIN" LED will be lit.) If a flame-out occurs, the RM7895 will lockout or recycle within 3-
seconds, depending on "jumper" configuration. Refer to Honeywell literature for proper
c o n f i g u r a t i o n .
R U N
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The RM7895 is now in R U N mode and will remain in run mode until the controller input opens,
indicating that the call for heat has been satisfied or a limit has opened. Once this occurs the RM7895
will sequence back to the S T A N D B Y m o d e .
N o t e s :
1 .
During S T A N D B Y and during RM7895 sequencing the "P O W E R" LED will blink
every four seconds. This is normal.
2 .
The "A L A R M" LED will be lit in the event of any flame failure.
3 .
To maintain proper operation of this device it M U S T be electrically grounded. Refer
to Honeywell RM7895 literature for criteria.
XIII Flame Safeguard
XII Main Automatic Valves
Continued
3. Redundant Solenoid Gas
Safety Valve