Gasmaster GMI 2M, Installation, Operation And Maintenance Manual

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IOM GMI 2M & 2ML Nov 2010.doc
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3.1 Sequence of Operation
3.1.1 Safety Loop
A: Components
Referring to Figure 2 (Control System Schematic) the safety loop includes the following
components:
I: High temperature cut off switch:
This is a manual reset switch and is normally
closed. It is installed on the outlet manifold. The desired high limit temperature
can be set by the owner and is usually 10
°
F above the maximum operating
temperature. In no event should this switch be set at above 210
°
F. If the outlet
temperature increases above the set temperature, this switch will open and the unit
will go into the “lock-out” mode. The unit will remain in this mode until the
operator manually resets the switch.
II: Operating temperature switch:
This contact normally closes when the actual value
is less than the set point and is embedded in the temperature controller unit. The
desired outlet temperature (desired set point) is also set by the owner on the same
temperature controller.
III: Low water cut off switch:
This switch in the safety loop is installed at the end of
manifold. The switch is normally open, and as soon as water level in the system
reaches the point where the switch is installed, it will close.
IV: Remote Enable/Disable Terminals:
There are “Remote Enable/Disable” terminals
in the control panel. These terminals can be used for the BMS connections, if
required.
V: Low gas pressure switch:
A manual reset low gas pressure switch is installed on
the gas train between the gas pressure regulator and the first safety shut off valve
(please see item #4 on the schematic diagram “Typical UL Schematic Gas Piping”
on page 9 of the Riello catalogue). If the line pressure drops below 8” wc, the
switch will open and the unit will immediately shut down.
VI: Air Pressure Switches:
One low air pressure switch is installed on the side of the
blower and measures air pressure entering the burner (for exact location of the
switch please see item #14 on the drawing presented on page 4 of the Riello
catalogue). If the combustion air pressure drops by more than 20% below the
nominal air pressure (minimum pressure of 0.4” wc), the burner controller will be
deactivated and the main gas valve will immediately close.
.