Columbia CT-10, Installation, Operation And Maintenance Manual, Page: 22 / 56

COLUMBIA BOILER COMPANY, REV 2-17
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Low Water Cut-Off
The manual reset “probe” is used as a supplementary safety device for protecting the boiler
against damage from low water. It is designed to operate if the water level control low
water cut-off should fail to operate for any reason. This unit is set to operate at a water
level in the boiler lower than that of the water level control. See drawing CT-415 in the
appendix for installation of probe rod.
This unit consists of a circuit board design with one normally open (N.O.) non-powered
contact. When reset, it completes a circuit between the probe rod and the boiler drum,
through the water in the boiler. If the water level falls below the probe rod, the circuit is
broken causing the contact to open, breaking the circuit to the burner and energizing an
alarm circuit (if equipped).
NOTICE: This relay must be reset after a low water condition has been corrected or after
any interruption in the electrical supply.
DESCRIPTION OF OPERATING CONTROLS AND SAFETY DEVICES
Operating Pressure Control
This switch opens on pressure rise. It should be set at the maximum operating pressure
desired.
Do not set the operating pressure higher than 135 PSI. The differential deter-
mines when the burner will restart. The differential should be set at a value as large as pos-
sible to keep the unit from short cycling.
The pressure control must be level in order to operate accurately. It is level when the level-
ing indicator hangs freely with its pointer directly over the index mark inside the back cover
of the case.
The upper operating or cut-off pressure is determined by the main scale set point, while the
lower operating or cut-in pressure is determined by the main scale operating point minus
the differential.
Adjust the main scale set point for the desired operating pressure by turning the main scale
adjusting screw on top of the case until the main scale setting indicator is at the desired
pressure. Adjust the differential set point for the desired cut in pressure by turning the
adjusting screw on top of the case until the differential setting indicator is at the desired
setting.
Safety Limit Pressure Control
The Safety Limit operates essentially the same as the pressure control described previously
except this limit is equipped with a reset button and does not have a differential. The pur-
pose of the Safety Limit is to shut down the burner if the operating pressure control becomes
inoperable and steam pressure continues to climb. The burner will not start until the situa-
tion is corrected and the reset button is pushed. The high limit of the Safety limit must be
set above the operating pressure control setting.
NOTICE