750-204
Profire D/LND
1-11
1.9 — Gas System
1.9.1 — Main Gas Train Components
Depending on the requirements of the regulating authority, the gas control system and gas train may consist of
some, or all, of the following items:
FIGURE 1-10. Gas Train Components
Component Description
Gas Volume Valve The butterfly type valve is positioned by linkage from the modulating motor and
controls the rate of flow of gas.
Main Gas Valves Electrically operated safety shutoff valve(s) that open to admit gas to the burner.
Standard UL burners include:
• Models D42: One motorized gas valve and one solenoid valve.
• Models D54-105: One motorized gas valve w/closure interlock and one sole-
noid valve.
• Models D145-420: Two motorized gas valves and one w/closure interlock.
Main Gas Regulator Regulates gas train pressure to specified pressure required at the inlet to the gas
train. Input is set by main gas pressure regulator adjustment.
Main Gas Cocks For manual shutoff of the gas supply upstream of the pressure regulator. A sec-
ond shutoff cock downstream of the main gas valve(s) provides a means of test-
ing for leakage through the gas valve(s).
High Gas Pressure Switch A pressure actuated switch that remains closed when gas pressure is below a
pre-selected setting. Should the pressure rise above the setting, the switch con-
tacts will open causing main gas valve(s) to close. This switch requires manual
reset after being tripped.
Low Gas Pressure Switch A pressure actuated switch that remains closed when gas pressure is above a
pre-selected setting. Should the pressure drop below this setting, the switch
contacts will open, causing main gas valve(s) to close. This switch requires
manual reset after being tripped.
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