CHAPTERS
K.
HIGH
LIMIT
TEMPERATURE
CONTROL
(Hot
Water)
Set
the
"cut-out" (burner off) temperature on
the
scale using
the
adjusting screw.
This
control will
break the circuit
and
lock out on a rise
in
water
temperature above
the
setting. The setting should
be
sufficiently above
the
operating limit tempera-
ture
to
avoid unnecessary shutdowns.
On
a 30
lb.
hot
water boiler,
the
setting
is
not
to
exceed
240°
F.
The control requires manual resetting after
tripping on a temperature increase.
To
reset,
allow water temperature
to drop below
the
cut-
out setting less differential,
and
then
press
the
manual reset button.
L. LOWWATERCUTOFF.
DEVICES
(Steam
and Hot
Water)
No
adjustment
is
required since these controls
are
· preset
by
the
original manufacturer. However, if
water level
is
not maintained
as
shown
in
Figure
2-3, inspect these devices immediately and
replace
as
required.
M.
COMBUSTION
AIR
PROVING
SWITCH
Air pressure against
the
diaphragm actuates
the
switch which, when closed, completes a circuit
to prove the presence
of
combustion
air.
Since
the
pressure
of
the
combustion air
is
at
its
mini-
mum
value when
the
damper
is
full
open,
the
switch should
be
adjusted under
that
condition.
It should
be
set slightly below
the
minimum
pressure, but
not
so
close
as
to
cause nuisance
shutdowns.
750--150
ADJUSTMrnNTPROCEDURES
The run/test switch on
the
program relay should
be
set to TEST. Tum
the
burner switch on. The
blower will start (provided that all limit circuits
are
completed)
and
the
programmer will proceed
through the prepurge portion
of
the
sequence,
stopping at
the
low fire prepurge position.
NOTE:
On
an
oil fired boiler,
the
atomiz-
ing air proving switch (AAPS)
must also
be
closed.
On a combination fuel fired
burner,
the
fuel
selector switch
could
be
set
at
"gas" to eliminate
the
atomizing air proving switch
from
the
circuitry.
To
have the modulating damper motor drive
to
high fire (damper open), remove
the
cover
from
the
motor
and
remove
the
wire
from
terminal
W.
Slowly tum down
the
·air
switch adjusting screw
until
it
breaks the circuit. At this point
the
programmerwilllockout
and
it
must
be
manually
reset before it can
be
restarted.
Add
a half tum or
so
to
the
adjusting screw to remake
its
circuit.
Recycle the program relay
to
be
sure that normal
operation
is
obtained. Replace
the
wire on ter-
minal
Wand
reinstall
the
cover. Return
the
test
switch to the
RUN
position.
N.
ATOMIZING
AIR
PROVING
SWITCH
Air pressure against
the
diaphragm actuates
the
switch which, when closed, completes a circuit
to prove the presence
of
atomizing air. Since
the
pressure
of
the
atomizing air
is
at
its
minimum
value when there
is
no
fuel
present
at
the
nozzle,
adjustment
of
the
switch should
be
done while
the
unit
is
running but not firing. The control
should
be
set slightly below
the
minimum
pres~
sure,
but
not
so
close
as
to
cause nuisance shut-
downs.
CHAPTER
5~9
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