12
a. Setting The Differential
On the far left side of the pressuretrols is the
differential indicating scale labeled "DIFF". Turn the
differential adjusting screw until the indicator aligns
with the desired differential. A minimum differential
will maintain the boiler pressure closer to the set
point. A larger differential will help prevent rapid on
and off cycling of the boiler.
4. Limit
The limit switch is similar in operation to the controller
but has a slightly higher set point. If the controller fails
to shut off the boiler and the steam pressure continues
to rise, the limit switch will shut down the boiler. The
controller is an operating switch; the limit serves as an
auxiliary safety cut-off. The limit switch is supplied with
a manual reset function. If the steam pressure trips the
high limit switch, the limit locks in the off position. The
limit switch will not reset until the manual reset lever is
pressed.
a. Setting The Limit
This is done using the same procedure as for the
controller. The limit setting will be slightly higher than
the controller's set point.
Low pressure boilers (less than 15 psi): Set the limit
switch 4 psi higher than the controller and 3 psi
lower than the safety valve setting.
High pressure boilers (greater than 15 psi): Set the
limit switch at least 10 psi higher than the controller
and 5 psi lower than the safety valve setting.
5. Night Operating Pressure Switch
A third pressure switch may be supplied as an option.
This switch allows the boiler to operate at low pressure
at night for heating the building. Set the night operating
pressure switch at approximately 10 psi.
6. Example
Boiler with a 100 psi safety valve. Set the controller at 80
psi with an 8 to 10 psi differential. Set the limit switch at
90 psi. Turn on the boiler, burner will fire. When the
steam pressure reaches 80 psi, the controller shuts
down the burner. When the pressure drops to 70 to 72
psi the burner restarts. The boiler continues to cycle to
maintain 80 psi. If for some reason the steam pressure
should rise to 90 psi, the limit switch shuts off the boiler.
The manual reset on the limit switch must then be reset
before the boiler will operate again.
10. More Information
For any additional information on the Honeywell
Pressuretrols, refer to the Honeywell product sheet in
the back of this manual.
O. Start Up of Standard Burners
CAUTION:
All work performed on gas fired equipment
or gas train components must be done by qualified
personnel.
1. Spark-Ignited Pilots (Diaphragm or Motorized
Gas Valves)
a. Turn boiler switch OFF
b. Purge gas line
c. Turn OFF the main burner supply gas cock
d. Turn ON the pilot supply gas cock
e. Turn the boiler switch ON
f. Ignition transformer with spark and light the
pilot
g. Main gas valve will energize and open but will
not fire because main gas cock is closed
h. Check pilot for adequate flame signal (2.0 mV
minimum)
i. Slowly open main burner supply gas cock to
allow burners to light
j. If everything is normal, then adjust the main
gas pressure regulator for proper pressure
(4.25” w.c.)
k. Turn OFF boiler switch
l.
Turn ON boiler switch
m. Check for proper ignition and cycle several
times
2. Spark-Ignited Pilots (Combination Gas Valves)
a. Turn boiler switch OFF
b. Attach pilot tubing and red ignition wire if not
previously installed
c. Purge gas line
d. Position control knob on combination gas valve
to ON
e. Turn boiler switch ON
f.
Pilot should spark, causing pilot to light
