Smith 8 series Installation And Operating Instructions Manual page 13

8 SERIES BOILER INSTALLATION AND OPERATING INSTRUCTIONS
PROBE LOW WATER CUT-OFF
Two different probe low water cut-offs are used on the
8-Series steam boilers as standard equipment. The
Hydrolevel model CG450-2060 is used on models
without the tankless coil, the CGT450-2060 probe
low water cut-off is used on models with the tankless
coil. The probe low water cut-off senses water level by
sending an electrical current through a metallic probe
mounted in the water jacket of the boiler. If water is
surrounding the probe the current will travel through
the water to the metal casting and back to the control.
The control will then enable the boiler to run. Hydrolevel
recommends cleaning the probe yearly using a nylon-
cleaning pad.
Hydrolevel has developed a "CycleGuard" feature that
uses a timer to shut the boiler down at regular intervals
for a "still water test". The still water test allows time for
foam and condensate to settle before determining the
true water level. This feature prevents foam and wave
action from generating a false high water level. The
Hydrolevel CG450-2060 control is used on all 8-Series
steam boiler that are not equipped with the tankless
coil. The 2060 suffi x in the part number refers to the
CycleGuard timing. This timing will allow the boiler to
run for 20 minutes and then will provide a 60-second still
water test. It is the CycleGuard feature, which in many
situations is instrumental in protecting boilers during low
water conditions. Foaming is the most diffi cult problem to
overcome with a probe low water cut-off because it has
the same electrical properties as water. Lab experience
has shown that many boilers can have a severe foaming
situation even though the sight glass remains still and
crystal clear. To make matters worse, the generation
of foam often increases as the water level drops and
approaches the top of the crown sheet. The still water
test cycle has a minimum effect on the boiler heating
capacity. The boiler will resume a full rolling boil within 3
to 5 seconds of completing the still water test.
Water levels may fl uctuate below the minimal safe level
momentarily as a result of waves generated by the boiling
action. There is a timer delay function programmed into
the control that prevents the boiler from shutting off
unless the low water condition lasts longer than 10-12
seconds. This allows enough time to eliminate nuisance
shutdowns and yet the duration is short enough to
prevent damage to the boiler in the event of a real low
water condition.
The Hydrolevel control used on the 8-Series steam
boilers has another feature called the SmartCycle. This
feature allows the timer to be reset at the start of each
call for heat to provide a full 20 minute run time between
still water testing. Without this option a boiler with a 2060
control timing that ran for 18 minutes on one call for heat
will only run for 2 minutes on the next call for heat before
shutting down for the still water test. This can appear
to be a "boiler short cycling problem" when in fact the
control timer is just fi nishing up the 20-minute cycle.
The Hydrolevel control is constantly testing for low water
even during standby when the boiler is idle. Testing is not
limited to the still water test period. Therefore every call
for heat essentially starts with a low water test. Through
testing it was determined the 8-Series boiler could run
for 20 minutes without needing a still water test. To utilize
this option an orange wire is connected from the burner
to the Hydrolevel control at the "Burner" terminal. This
wire sends a signal to the control each time the burner is
energized resetting the CycleGuard timer. This allows
the boiler to run a full 20-minute cycle on each call for
heat, or until the call for heat is satisfi ed.
For steam boilers equipped with a tankless coil there
is another SmartCycle feature that suspends the still
water test until the demand for domestic hot water is
satisfi ed. Normally after the still water test the boiler
is back to a full boil in a few seconds, but cold water
fl owing through the tankless coil during this test period
can cause the boiler water temperature to drop. On
smaller boilers the burner output may not be enough
to allow the water temperature to rebound and still
produce domestic hot water. Steam boilers sold with
the tankless coil are provided with a control with a "T"
in the part number. The CGT450-2060 control will have
two extra pairs of terminals. There is a pair of terminals
labeled "Low Limit". These terminals connect to an
aquastat that measures the boiler water temperature
near the tankless coil. The second set of terminals
labeled "Thermostat" will connect to the T-T terminals on
the burner in parallel with the building thermostat. This
feature will suspend the still water test whenever the low
limit aquastat determines that the boiler is being used
to produce domestic hot water. This will help assure the
boiler maintains suffi cient temperature for the tankless
coil to produce the hot water required.
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