Profire V Burner Chapter 2
750-177 2-7
D. GAS SYSTEM
Gas is introduced into the combustion zone from a circular manifold through multiple ports in the manifold.Firing rate
is determined by the size and number of ports, by manifold pressure, and by combustion zone pressure. The firing
rate is regulated by a rotary, butterfly-type throttling valve at the manifold inlet. The valve is actuated by adjustable
linkage from the modulating motor. Depending upon specific requirements, one or two gas safety shutoff valves are
provided for installation in the gas train upstream of the butterfly valve. Safety shutoff gas valves are wired into the
programming control to automatically open and close at the proper time in the operating sequence.
MAIN GAS TRAIN COMPONENTS
Depending upon the requirements of the regulating authority
, the gas control system and gas train mayconsist of
some, or all, of the following items:
Gas Volume Valve The butterfly type valve is positioned by linkage from the modulating motor and controls the gas flow rate.
Main Gas Valves Electrically operated safety shutoff v
alve(s) that open to admit gas to the burner.lowfire Standard UL burn-
ers include:
• Models V13-25: diaphragm gas valve & sol
enoid valve
• Models V30-50: one (1) motorized gas valve w/proof of closure or two (2) safety shutoff valves
• Models V55-120: one (1) motorized gas valve w/proof of closure and one (1) safety shutoff valve
• Models V126-168: two (2) motorized gas valves (two moto
rized gas valves can be optionally provided
on all models)
Main Gas Regulator Regulates gas train pressure to specified pressure required at the
burner manifold.Input is set by main gas
pressure regulator adjustment.
Main Gas Cocks Used for manual shutoff of the gas su
pply upstream of the pressure regulator. A second shutoff cock
downstream of the main gas valve(s) provides a means of testing for leakage through the gas valve(s).
High Gas Pressure Switch
(Mo
dels V30-168)
A pressure actuated switch that remains closed when gas pressure is below a selected setting. Should the
pressure rise above the setting, the switch contacts will open causing the main gas valve(s) to close. This
switch requires manual reset after being tripped.
Low Gas Pressure Switch
(Mo
dels V30-168)
A pressure actuated switch that remains closed when gas pressure is above a 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.
OPERATION: Metered gas flows through the main gas shutoff cock, through the pressure regulator to the automatic
gas valves and butterfly valve to the gas manifold.
The butterfly gas valve modulates flow to burner input demand
. The butterfly valve is positioned through mechanical
linkage by the modulating motor. The air control damper is positioned simultaneously by the modulating motor.
The automatic gas valve(s) cannot be energized unles
s the combustion air proving switch is closed. The low and high
gas pressure switches must be closed to prove proper gas pressure.
A normally open vent valve, if required, is located between the
two automatic gas valves. This valve is shut when the
automatic gas valves are open. When the automatic valves are closed, the vent valve is open for venting gas to the
outside, should any be present.
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