Garland G Series, Техническое справочное руководство, Страница: 66 / 108

Part # GCTRM Rev 3 (12/10/09) Page 66
Gas Technician’s Glossary
Air-Gas Ratio: The ratio of combustion air supply flow rate to
the fuel gas supply flow rate.
Air Shutter: An Adjustable shutter on the primary air
opening of a burner, which is used to control the amount
of combustion air introduced into the burner body.
Atmospheric Pressure: The pressure exerted upon the earth’s
surface by the weight of atmosphere above it.
Automatic Gas Pilot Device: A gas pilot incorporating a
device, which acts to automatically shut off the gas
supply to the appliance burner if the pilot flame is
extinguished.
British Thermal Unit (BTU): Is the heat energy produced
when burning a fuel gas. It is defined as the quantity of
heat required to raise the temperature of one pound of
fresh water one degree F. An ordinary wooden match
produces approximately 1 BTU of heat.
Butane: A hydrocarbon fuel gas heavier than methane and
propane and a major constituent of liquefied petroleum
gases.
Combustion: The rapid oxidation of fuel gases accompanied
by the production of heat or heat and light.
Combustion Air: Air supplied in an appliance specifically for
the combustion of a fuel gas.
Combustion Chamber: The portion of an appliance within
which combustion normally occurs.
Combustion Products : Constituents resulting from the
combustion of a fuel gas with the oxygen in air, including
the inert, but excluding excess air.
Cubic Foot of Gas (Standard Conditions): The amount of gas
that will occupy 1 cubic foot when at a temperature of
60°F, and under a pressure equivalent to that of 30 inches
of mercury.
Density: The weight of a substance per unit volume. As
applied to gas, the weight in pounds of a cubic foot of
gas at standard pressure and temperature.
Dewpoint: The temperature at which a vapor will start to
condense into its liquid form.
D .M .S .: Drill Manufacturer’s Standard equivalent to Standard
Twist Drill or Steel Wire Gage numbers.
Draft Hood (draft diverter): A device built into an appliance,
or made part of a vent connector from an appliance. It is
designed to: 1) assure the ready escape of the products
of combustion in the event of no draft, backdraft, or
stoppage beyond the draft hood; 2) prevent a backdraft
from entering the appliance; 3) neutralize the effect of
stack action of a chimney or gas vent upon the operation
of the appliance.
Downdraft: Excessive high air pressure existing at the outlet
of chimney or stack, which tends to make gases flow
downward in the stack.
Excess Air: Air that passes through an appliance and the
appliance flues in excess of that which is required for
complete combustion of the gas. Usually expressed as a
percentage of the air required for complete combustion
of the gas.
Extinction Pop: This is merely flashback occurring when a
burner is turned off. It is usually instantaneous although
it can occur several seconds after the burner has been
turned off. What happens is that primary air continues
to flow into the burner even though the gas jet has been
cut off and does not inject air. The mixture in the burner
changes from the normal operating mixture to all air
and flow rate through the ports falls towards zero. Under
these conditions, it is possible for the flame speed to
exceed flow velocity at some instant and flashback may
occur. The result is a tiny explosion or pop. Increasing
primary air input will reduce the flashback tendency.
Fahrenheit: The common scale of temperature measurement
in the English system of units. It is based on the freezing
point of water being 32ºF and the boiling point of water
being 212ºF at standard pressure conditions.
Flame Speed: Speed at which the flame front moves toward
the air-gas mixture issuing from the burner port. It
depends on the quantity of air-gas mixture and type of
gas.
Flame Stability: Primary air, Flame speed, port size and
port depth are several factors affecting flame stability.
Flames on a burner tend to stabilize at a point where
flow velocity out and burning speed back are equal. This
balance of flow velocities and burning speed explain why
flames change when primary air or gas rate is adjusted.
Flame Temperature: Maximum is reached when perfect
combustion is achieved.