M-Series Technical Manual
93
Cambridge Air Solutions
IGNITER (IG)
The hot surface igniter is the ignition
source for lighting the gas in the
burner. It is made of silicon carbide
which is very fragile. Care should be
used in handling. It operates on 24
Volts and the current ranges from 1.3 to 1.7 amps. It will
reach temperatures in excess of 2400˚F during the
ignition trial. It is furnished with a sleeve for shock
mounting and sealing the igniter in the mounting tube.
INTERIOR LIGHT(S)
Available for the heater cabinet, electrical
control enclosure,
and/or gas train
enclosure. Light switches are located inside
the heater’s electrical enclosure. Furnished
with safety guards. 100 watts maximum,
each. A separate electrical supply
source is required.
LEAK TEST FACILITY (SW4)
The leak test facility is provided on
all heaters over 400,000 Btu/hr and
consists of a momentary switch for
the first safety shut-off valve in the
gas train and a gauge port between
the first and second safety shut-off
valve. By holding the gas valve
momentary switch closed, the first
gas valve is energized which allows
gas pressure to build on the seat of the second gas valve.
The gauge port between valves is used to determine if
the first gas valve seat is properly sealed.
MODULATING VALVE (MV)
The modulating valve responds
to a 4 to 24 Volt DC signal
from the amplifier to modulate
the flow of gas to the burner. On
the Maxitrol M511 or M611
valve, the minimum fire adjusting
screw is located on the far side
of the valve under the dust cover. On the Maxitrol
MR212 valve, the minimum fire adjusting screw is located
under the large dust cover. The MR212 modulating valve also
serves as the manifold pressure regulator to control the
burner manifold pressure. The MR212 is rated for 5
PSIG.
COMBINATION VALVE
The combination valve serves as a
manifold pressure regulator and redundant
gas shut-off valve. This control is typically
used for gas capacities below 400,000 Btu/hr.
The valve operates on 24 Volts AC power.
The combination valve is rated for a
maximum gas supply pressure of 14 inches WC.
MANIFOLD PRESSURE REGULATOR
The manifold pressure regulator
controls the burner manifold pressure.
When the MR212 valve is used, this
modulating valve also serves as the
pressure regulator. The maximum gas
supply pressure rating is normally
determined by the exposed pressure
rating of the regulating device. The RV61 and RV81 are
rated at 1 PSIG; and the MR212 is rated at 5 PSIG. (For
make-up air heaters rated at 400,000 Btu/hr or below, see
the combination valve above.)
MOTOR STARTER (MS), OVERLOAD (OL),
& AUXILIARY CONTACT (AX, AX1)
The motor starter assembly consists of a
motor starter, overload relay and auxiliary
contact. The overload relay protects the
motor from excessive current or single
phasing. If the overload relay trips, it must
be reset manually. The auxiliary contacts
are used in the gas valve safety circuit as
an indication the blower is operating,
and as an optional exhaust fan contact for interlocking
other equipment with the operation of the heater.
