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SECTION 4 PRINCIPLES OF OPERATION
4.1
GENERAL
The
Stearn-l
t
cooker consists
of
a cooking
compartment
into
which
pans
of food
are
loaded
through
an
inward
opening
door.
The
compartment
is filled
with water
(for steam
generation)
which
is heated
by gas burners
located
under
the
cooking
compartment.
The
gas burners
are ignited
by a
pilotless,
direct
spark
(electrode)
ignition
system
which
is
electrically
controlled
by
the
ignition
control
board.
Internal
compartment
pressure
is
regulated
by the
exhaust
system
which
is
mounted
at the top rear
of
the
cabinet.
The
pressure
may
be monitored
(by the operator)
by viewi ng the pressure
gauge
which
is con-
nected
in
the
steam
pressure
line. Cooking
cycles
are
controlled
by
a 60-minute
electric
timer
which
is
mounted
on
the lower
front
panel.
4.2 DETAILED
OPERATION
With electrical
power
applied,
gas supply
valve
open and
the timer
set
to
the
desired
cooking
time,
the
electrical
control
circuits
are
activated.
The
exhaust
valve
closes
automatically
and
the
burner
electrodes
are
energized.
Gas
passes
through
the
gas
regulator
and
valve
body
to
the
burners
where
the gas
is
ignited
by the
direct
spark
ignition
electrodes.
The
gas
flame
on
the
main
burner
heats
the water
in
the
cooking
compartment
and
within
a few
minutes,
steam pressure
begins to build
up.
4.3
STEAM CIRCUIT (Figure 4·1)
The steam
circuit
consists
of the steam
pressure
gauge,
steam
trap
assembly,
pressure
switch,
steam
exhaust
valve
assembly
(including
an
exhaust
valve
silencer),
a 15
psi
pressure
relief
valve
and
associated
steam
circuit
fittings.
These
are
shown in Figure
4·1.
4.3.1 Steam Trap
As the pressure
builds
up in the
cooking
compartment,
cold
air is forced
out of the
compartment
through
the
thermostatic
steam
trap
located
in the collar
at the
top
rear of the Steam·lt.
The air will continue
to
escape
as pressure
builds
up and the steam
trap
will close
after
all
the
air
has been
forc-
ed out
of
the cooking
compartment
4.3.2 Pressure
Switch
When
the pressure
reaches
9 to 10 psi
(the
Steam-It
is
set
to operate
at
15
psi)
of
pressure
the
contact
on
low
pressure
switch
(Close on Rise) will close, thereby
closing
the
circuit
to the
clock motor and starting
the ac-
tual
cooking
time
period.
When the pressure
in
the
cooking
compartment
reaches
15
psi,
the contacts
on high
pressure
switch
will
open
These
contacts
being
wired
in series
with the
cycling
coil of the
gas valve
(through
the ignition
control
board),
will shut off gas
to the main
burner when
they
are
open,
caus-
ing the pressure
to
stop
rising.
When
the
cooking
compartment
cools
and the pressure
drops
to
13
psi, the
con-
tacts
on
the
high pressure
switch
(Open on
Rise)
will
close,
gas
will
flow
to
the
main
burner
and be
reignited
by the
electrodes.
Any
number
of such
"OFF"
and
"ON"
cycles
might
occur
during
the
selected
cooking
time.
4.3.3 Steam Pressure
Gauge and Safety
Relief
Valve
Located
at the top
rear
of
the Steam-It
and
mounted
into
the forward
face of the flue
for
visibility,
the
Steam
Gauge
registers
the
pressu re
within
the
Steam-It
cooking
compartment.
The
Safety
Valve
is set to
automatically
relieve
the
cooking
compartment
of
ex·
cessive
pressure
buildups
by opening
at a
point between
151/2
psi
and 16
psi.
4.3.4 Steam Exhaust
Valve and
Silencer
The steam
exhaust
valve is located
in the
collar
at the top rear of the Steam-lt
and it
lets the pressure
escape
from the cornpart-
ment
when
the
timer
is shut
off. When
the
timer is turned
on this valve is closed
permit-
ting the pressure
to build
up.
To overcome
objectionable
noises,
the
exhaust
valve
is equipped
with
an exhaust
silencer
which
will permit
the exhaust
valve
_
to release steam at the end of the cooking
cv-
cle without any objectionable
noises.
4·1
S2127
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