Midco Unipower G-Series - Manual (Page 13)

X Blower and Motor
Continued
XI Gas Pressure Regulator
XII Main Automatic Valves
1. Diaphragm Main
Automatic Valve
2. Motorized Main
Automatic Valve
13
■ ■ Proof of blower operation is provided by the diaphragm air switch, which must close its contacts and
maintain them closed when the blower is running. In case of malfunction, the air switch should be
r e p l a c e d .
■ ■ The gas pressure regulator is used to automatically reduce and maintain constant gas pressure to the
burner. To vary 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.
■ ■ Maximum and minimum allowable gas pressures are shown in Table 1. Because these regulators are
of the low pressure type with metal seats, leakage through the seat will cause outlet pressure to rise
equal to inlet pressure during burner shutdown. Therefore do not subject the burner to inlet pressures
above those listed (14" W.C.). For higher inlet pressure, See Section VI P i p i n g for instruction on
installing alternate regulators.
■
■ The vent in the upper diaphragm case normally breathes air but should be vented to the outside for
protection in the event of a punctured diaphragm. See Section VI P i p i n g for proper venting procedures.
Never connect the regulator to the diaphragm valve vent.
■ ■ When the regulator is to be installed or replaced, take care not to distort the body casting. Apply
wrench only to the heavy body section adjacent to the pipe thread.
N o t e : All burners are equipped with dual valves. Select the type you have and reference. Burner
construction for special codes and/or insurance requirements such as Factory Mutual or Industrial Risk
Insurers may require alternate construction. (Refer to Section XIV Special Equipment.)
Employed with Redundant Solenoid Valve.
■ ■ The Honeywell V48A diaphragm valve supplied on standard On-Off and Full Modulating Unipower
burners is of the slow opening, fast closing type and requires venting to the bleed connection on the
burner box. Closing force combines a gas pressure differential, diaphragm weight and spring.
■ ■ When the controller is not calling for heat, the coil is de-energized. The plunger of the three way
actuator is in the down position, so that the bleed is closed and the supply port is open. Gas flows to
the top diaphragm, causing the gas pressure and spring to hold the valve closed.
■ ■ With a call for heat, the flame safeguard energizes the coil. This pulls the plunger to the up position,
opening the bleed valve and closing the supply port. The gas then bleeds off the top of the diaphragm,
allowing the gas pressure below to lift the diaphragm, allowing the gas pressure below to lift the
diaphragm and open the valve. When all the gas has bled off the top of the diaphragm, the valve is fully
opened. In the event of a power failure during operation, the valve will close. Normal operation will
resume upon restoration of power.
■ ■ For general service, tests for gas tightness and proper operation will suffice. If leakage is observed,
replace valve. If the valve will not open, make sure that normal gas pressure is available at the valve, the
bleed line is unobstructed and power is available at the terminals.
■ ■ 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 a malfunction is found to be caused by the valve operator head, the
entire valve must be 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.
Employed with Redundant Solenoid Valve, or Second Motorized Valve.
■ ■ Motorized Main On-Off Valves are available on special order. A 2-Step actuator combined with a
characterized guide is standard on 2-Step Unipower burners.
■ ■ 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 if burner is supplied as On-Off, Low Fire Start, or as a 2-
S t e p .
Figure 14: Drawer Assembly