Midco Unipower A-Series - Manual (Page 11)

XI Blower and Motor
XII Gas Pressure Regulator
XIII Main Automatic Safety
Shut-Off Valve
V48 Diaphragm Gas Valve
(Not for use in Canada)
V5055 Valve Body
with Motorized Actuator
■ ■ ■ ■ No routine service is necessary on the blower system other than cleaning the blower wheel
when necessary.
■ ■ ■ ■ Blowers using three-phase motors will run in either direction depending on the connection of
the power supply. On new installations, motor replacement or power supply disturbance, the
rotation must be checked. Corrections can be made by interchanging any 2 wires of the three-
phase power supply.
■ ■ ■ ■ If replacement motors for standard burners are procured from a source other than Midco, they
should conform to the following specifications: 3450 RPM, Frame 56C, end mounted open motor
with ball bearings. Capacitor start and thermal overload protection if single phase.
■ ■ ■ ■ Proof of blower operation is provided by the diaphragm type blower air switch, which must
close its normally open contacts and maintain them closed when the blower is running. A check
for proper operation can be made by disconnecting the air pressure tube during burner
operation, which should result in burner shut-down. In case of malfunction, it is recommended
that the air switch be completely replaced.
■ ■ ■ ■ A three wire self-testing hookup of the air switch is used on burners equipped with flame
safeguards, such as the RM7840, which have a 120V air proving interlock circuit. The N.C.
contacts of the air switch are wired into the start interlock circuit, which prevents burner start-up
unless the air switch proves operational by returning to its normally off position after every burner
run. Failure of the burner to start may be caused by a faulty air switch.
■ ■ ■ ■ The gas pressure regulator is used to automatically reduce and maintain constant gas pressure
at the burner.
■ ■ ■ ■ To adjust the outlet pressure, remove the seal cap for access to the adjusting screw. Turning
the screw clockwise will increase outlet pressure, counter-clockwise will decrease outlet pressure.
■ ■ ■ ■ The vent in the upper diaphragm case normally breathes only air and 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 unconnected.
The vent must never be connected to the burner or combustion chamber
■ ■ ■ ■ Although regulators seldom require servicing, the most vulnerable part is the diaphragm.
Periodic service should be limited to a diaphragm inspection, which should be checked for
punctures of stiffness.
■ ■ ■ ■ The Honeywell V48A diaphragm gas valve is of the slow opening type with a maximum closing
time of 5 seconds. It requires a bleed tube which discharges into the combustion chamber
adjacent to the pilot. Closing force combines a gas pressure differential, diaphragm weight and
spring.
■ ■ ■ ■ For general service a check for gas tightness will suffice. Start the burner and observe through
at least one cycle to be sure the valve functions properly and that the main flame has
extinguished completely.
■ ■ ■ ■ Leak test per Section XVI Special Equipment. If leakage is observed, turn off the electrical
power and the main manual gas valve, remove the diaphragm case and make the following
checks: (1) the diaphragm must be pliable, free of holes and must have sufficient slack when set
in position; (2) the valve seat must be free of gum, tar or other dirt and must be free of cuts,
nicks and worn spots.
■ ■ ■ ■ If the valve fails to close, make sure power is off at the terminals and gas flow is in the
direction of the arrow on the valve body. When malfunction is determined to be caused by the
valve operator head, the operator head should be completely replaced.
■ ■ ■ ■ If the valve will not open, make sure normal gas pressure is available at the valve, the bleed
line is unobstructed, and power is available at the terminals.
■ ■ ■ ■ The Honeywell V5055 main valve body is of the slow opening, fast closing type and does not
require venting. It is powered by a motorized valve actuator which supplies the motive power for
opening and closing the valve. The V4055 Actuator is used for On-Off and Full Modulating
operation. The V4062 Actuator is used for both the On-Off control and to provide High-Low
firing rate control. The full open position should be reached in 26 seconds after energization, the
closed position in one second or less.
■ ■ ■ ■ For general service, the valve should be checked for gas tightness and proper operation. If
leakage is detected, the valve seat should be examined for dirt, damage or obstruction.
■ ■ ■ ■ For access to the valve for inspection and cleaning, turn off the electrical power and the main
manual gas valve, then loosen the two Allen setscrews in the actuator collar and remove the
actuator. Remove the valve bonnet assembly by removing the bolts holding it to the valve body.
Inspect the valve seat for dirt, cuts, nicks and other defects. Do not disassemble the valve bonnet.
The valve seat is not replaceable; if defective, the entire valve body should be replaced.
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