Midco F400-33 - Manual (Page 8)

■ B) Insert the switch stem through the blower opening
until it just contacts the actuator disk. Then push in slow-
ly. The switch should "click" and the actuator spring
should compress approximately
1 Ú 8 " before the bracket
arms are seated. If conditions A and B are not met reset
switch location in the mounting bracket.
■ In both cases above check the results with an electri-
cal continuity test. The circuit across terminals C and NC
should be open when the blower is idle and closed when
the blower is running.
■ When shaft location of blower wheel is disturbed, re-
assemble with a 1 Ú 16 " clearance as shown in Figure 6.
XI GAS PRESSURE REGULATOR
The main gas pressure regulator is used to automatically
reduce and maintain constant gas pressure at the burn-
er. The regulator furnished as standard is suitable for a
maximum inlet pressure of 14.0"W.C. The springs in-
stalled provides for an adjustable outlet pressure range
of 2.0" to 5.0"W.C. and are factory set for 3.0"W.C. This
regulator is not of the Òtight shut-offÓ type and, conse-
quently, when the burner is on standby, the outlet pres-
sure will build up to equal the full inlet line pressure. Out-
let pressure settings must be checked while the main
gas is flowing.
■ To adjust the outlet pressure, remove the seal cap for
access to the adjusting screw. Turning the screw clock-
wise will increase outlet pressure, counter-clockwise will
decrease outlet pressure.
■ When the gas supply pressure is over 14.0"W.C.,
special regulators are required. See Section VI.
■ The vent in the upper diaphragm case normally
breathes only air, but must be connected to the outside
air to prevent escape of gas into the building in case of a
ruptured diaphragm. The vent line must be of sufficient
diameter, otherwise the restriction of air flow may cause
sluggish opening of the regulator. The effect can be
checked by comparing main flame start-up time with the
vent line connected and disconnected. The vent must
never be connected to the burner combustion cham-
ber.
■ When the regulator is to be installed, or replaced take
care not to crush the body casting. Apply wrench only to
the heavy body section adjacent to the pipe thread.
XII SOLENOID GAS SAFETY VALVES
(Main and Redundant Main; Standard Construction.)
When the valve operators are electrically energized the
plungers lift the valve disk off the valve seats, allowing
gas to flow. When the current is broken the valves close.
They will normally require no service. However, dirt or
foreign matter on the valve seats could cause leakage.
If leakage is detected or if the operator malfunctions re-
-8-
FIGURE 6 Motor, Blower, and Interlock Assembly
place the entire valve. After replacement check for leak-
age. If the valve is removed from the piping do not use
the operator assembly as a lever to turn valve. Apply
wrench on the valve body flat adjacent to pipe being re-
moved.
XIII OPTIONAL MOTORIZED MAIN
AUTOMATIC VALVE
(Employed with Redundant Solenoid Valve.)
■ Motorized Main On-Off, 2-Step, and Full Modulating
Valves, are available on special order. The redundant
and solenoid valve may be omitted if the motorized valve
includes optional "Proof of Closure Switch".
■ When the actuator is energized, hydraulic fluid is
pumped from a reservoir to a metal bellows. The bellows
transfers the resulting pressure through the drive stem to
open the valve. A separate spring return drive arm
operates the blower shutter.
■ For general service, the valve should be checked for
operation. The valve actuator may be removed from the
valve body, however, do not disassemble actuator; if
malfunction occurs, replace entire actuator assembly.
The valve body is also not field reparable. If leakage is
detected the entire valve body must be replaced.
XIV FLAME SAFEGUARD
WARNING: Explosion hazard. Do not use any
electronic device if it gets wet. It can malfunction
and cause serious injury or death. Replace any
device that has been wet.
■ Standard F400-33 and 400-33 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 XV 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 LEDÕs (light emitting
diodes) are provided to display sequence information.
Refer to the Honeywell RM7895 literature for detailed
operating information, configuration requirements,
testing, and service.