Gas Terms

Methane:

A hydrocarbon gas with formula CH4, one carbon atom linked to four hydrogen atoms. The principal component of natural gas.

Combustion Air:

Air supplied in an appliance specifically for the combustion of a fuel gas.

Injection:

Drawing primary air into a gas burner by means of a flow of fuel gas.

D.M.S.:

Drill Manufacturer's Standard equivalent to Standard Twist Drill or Steel Wire Gage numbers.

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.

Dewpoint:

The temperature at which a vapor will start to condense into its liquid form.

Liquefied Petroleum Gases:

The terms "Liquefied Petroleum Gases", "LPG" and "LP Gas" mean and include any fuel gas which is composed predominantly of any of the following hydrocarbons, or mixtures of them: propane, propylene, normal butane or isobutane and butylenes.

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.

Specific Gravity:

The weight of one cubic foot of gas compared to one cubic foot of dry air, at a common pressure and temperature. The specific gravity of a gas determines whether it will rise or fall when released into air. Air is given a specific gravity rating of 1.0. Since natural gases have a specific gravity of 0.4 to 0.8, it will rise when released into the air. Propane gas, however, with a specific gravity rating of 1.5 and butane gas 2.0 both will fall when released into air.

3. Mixer Throat:

(Venturi) That portion of the mixer which has the smallest cross-sectional area, and which lies between the mixer head and the mixer tube.

Soot:

A black substance, mostly consisting of small particles of carbon, which can result from incomplete combustion and appear as smoke.

Infrared Burner (Radiant Burner):

A burner, which is designed to operate with a hot, glowing surface. A substantial amount of its energy output is in the form of infrared radiant energy.

Universal Orifice:

A combination fixed and adjustable orifice designed for the use of two different gases, such as LPG and natural gas.

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.

Pressure Regulator:

A device for controlling and maintaining a uniform outlet gas pressure.

Vent:

A device, such as a pipe, to transmit flue products from an appliance to the outdoors. This term also is used to designate a small hole or openingfor the escape of a fluid. (such as in a gas control or regulator)

Soft Flame:

A flame partially deprived of primary air such that the combustion zone is extended and inner cone is ill-defined.

Manufactured Gas:

A fuel gas that is artificially produced by some process, as opposed to natural gas, which is found in the earth. Sometimes called "town gas".

Natural Gas:

A fuel which is derived from the earth consisting primarily of Methane (CH4). Natural gas is considered non-toxic and non-poisonous. Natural gas has little or no odor in its refined state. Odorants are added, such as mercaptan and sulphur compounds, to aid in leak detection.

Mixed Gas:

A gas in which the heating value of manufactured gas is raised by co-mingling with natural or LPG (except where natural gas or LPG is used only- for "enriching" or "reforming")

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.

Flashback Arrestor:

A gauze, grid or any other portion of a burner assembly used to avert flashback.

Butane:

A hydrocarbon fuel gas heavier than methane and propane and a major constituent of liquefied petroleum gases.

Propane:

A hydrocarbon gas heavier than methane but lighter than butane. It is used as a fuel gas alone, mixed with air or as a major constituent of liquefied petroleum gases.

Rich Mixture:

A mixture of gas and air containing too much fuel or too little air for complete combustion of the gas.

Venturi:

A section in a pipe or a burner body that narrows down and then flares out again.

Inches of Mercury Column:

A unit used in measuring pressures. One inch of mercury column equals a pressure of 0.491 pounds per square inch.

Inches of Water Column:

A unit used in measuring pressures. One inch of water column equals a pressure of 0.578 ounces per square inch. One inch mercury column equals about 13.6 inches water column.

Water Column:

Abbreviated as W.C. A unit used for expressing pressure.

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.

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.

Lean Mixture:

An air-gas mixture, which contains more air that the amount needed for complete combustion of the gas.

Flashtube:

An ignition device, commonly used for igniting gas on range top burners. An air-gas mixture from the burner body is injected into the end of ashort tube. The mixture moves along the tube, is ignited by a standing pilot flame at the other open end of the tube and the flame travels backthrough the mixture in the flashtube to ignite the gas at the burner ports.

Orifice:

An opening in an orifice cap (hood), orifice spud or other device through which gas is discharged, whereby the flow of gas is limited and/or controlled. (See also universal orifice)

Floating Flames:

An undesirable burner operating condition, usually indicating incomplete combustion in which flames leave the burner ports to "reach" for combustion air.

Flashback:

An undesirable flame characteristic in which burner flames strike back into a burner to burn there or to create a pop after the gas supply has been turned off. Flashback occurs when gas-air flow velocity is less than burning speed at some point near a burner port. Flashback is a condition where gas ignites within the burner. Any factor, which increases burning speed, tends to promote flashback, and any factor decreasing flow velocity from the ports will contribute to flashback. Flashback is more prevalent with faster burning gases. Natural gas is a relatively slow burning gas hence flashback is less likely. Reducing primary air is the usual cure for flashback.

Lifting Flames:

An unstable burner flame condition in which flames lift or blow off the burner port(s). Excessive primary air can cause flames to lift and blow off the burner ports, which can be noisy as well as inefficient. More importantly, however, is the production of dangerous carbon monoxide under this condition. Any factor, which reduces burning speed, promotes lifting flames. Also, any factor, which increases flow velocity from ports, contributes to lifting flames. Over-firing of burners is also a cause. The normal cure for lifting flames is the reduction of primary air input to the burner.

Port:

Any opening in a burner head through which gas or an air-gas mixture is discharged for ignition.

Products of Combustion:

Carbon dioxide and water vapor formed in burning plus the nitrogen in the reactants that entered with the combustion air.

Secondary Air:

Combustion air externally supplied to a burner flame at the point of combustion. It is the remaining air required for complete combustionbesides primary air.

Incomplete Combustion:

Combustion in which the fuel is only partially burned. A poorly vented appliance restricts flow of air into an appliance. Lack of ventilation around an appliance may lower oxygen content in the surrounding air. This can be a result of spillage of combustion products into the room as well. These conditions can cause incomplete combustion and poor performance of an appliance. Adequate, but not excessive ventilation is a must and cannot be over emphasized.

Combustion Products:

Constituents resulting from the combustion of a fuel gas with the oxygen in air, including the inert, but excluding excess air.

Downdraft:

Excessive high air pressure existing at the outlet of chimney or stack, which tends to make gases flow downward in the stack.

Updraft:

Excessively low air pressure existing at the outlet of a chimney or stack which tends to increase the velocity and volume of gases passing up the stack.

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.

Flame Temperature:

Maximum is reached when perfect combustion is achieved. Flame Velocity: The speed at which a flame travels through a fuel-air-mixture.Burning speeds vary with types of gases, and the amount of air mixed with the gas. This air to gas ratio is very important in that it is directly related to flame stability.

Utility Gases:

Natural gas, manufactured gas, liquefied petroleum gas-air mixtures or mixtures of any of these gases.

Inerts:

Non-combustible substances in a fuel, or in flue gasses, such as nitrogen or carbon dioxide.

Overrating:

Overrating is the operation of a gas burner at a greater rate than it was designed for.

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.

Vent gases:

Products of combustion from gas appliances plus excess air, plus dilution air in the venting system above a draft hood.

Ignition Temperature:

Temperature at which an air-gas mixture will initiate and support combustion.

Mixer:

That portion of a burner where air and gas are mixed before delivery to the burner ports.

2. Mixer Head:

That portion of an injection type burner, usually enlarged, into which primary air flows to mix with the gas stream

4. Mixer Tube:

That portion of the mixer, which lies between the throat and the burner head.

1. Mixer Face:

The air inlet end of the mixer head.

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.

Flue Gases, Flue Products:

The combination of combustion products and excess air leaving the combustion area. Since water is produced as a vapor in the burning of thegas, it is also present in the flue products. If the flue products and vent system remain hot enough, this vapor is harmlessly discharged. If not, the vapor can reach the dew point and condense into water, which can accumulate in the system.

Primary Air:

The combustion air introduced into a burner, which mixes with the gas before it reaches the burner port. Usually expressed as a percentage of air required for complete combustion of the gas. Ideal burning conditions generally is 10 cubic feet of air per cubic foot of gas.

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.

Manifold:

The conduit of an appliance, which supplies gas to the individual burners.

Input Rating:

The gas burning capacity of an appliance in BTU per hour as specified by the manufacturer. Appliance input ratings are based on sea level operation and need not be changed for operation up to 2 000 feet elevation. For operation at elevations above 2 000 feet, input ratings should be reduced at the rate of 4 percent for each 1 000 feet above sea level.

Manifold Pressure:

The gas pressure in an appliance manifold, upstream of burner orifices.

Flue Loss:

The heat lost in flue products exiting from the flue outlet of an appliance.

Port Loading:

The input rate of a gas burner per unit of port area, obtained by dividing input rate by total port area. Usually expressed in terms of BTU per hour per square in of port area.

Natural Draft:

The motion of flue products through an appliance generated by hot flue gases rising in a vent connected to the furnace outlet.

Primary Air Inlet:

The opening or openings through which primary air is admitted into a burner.

Flue Outlet:

The opening provided in am appliance for the escape of flue gases.

Combustion Chamber:

The portion of an appliance within which combustion normally occurs.

Atmospheric Pressure:

The pressure exerted upon the earth's surface by the weight of atmosphere above it.

Viscosity:

The property of a fluid to resist flow.

Input Rate:

The quantity of heat or fuel supplied to an appliance, expressed in volume or heat units per unit time, such as cubic feet per hour or BTU per hour.

Combustion:

The rapid oxidation of fuel gases accompanied by the production of heat or heat and light.

Air-Gas Ratio

The ratio of combustion air supply flow rate to the fuel gas supply flow rate.

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.

Yellow Tipping of Flames:

Too severe a reduction in primary air also causes its problems. Yellow tipping is one of them. Flames will eventually become all yellow if no primary air is supplied. Glowing carbon particles in the flame cause these yellow tips. Soot will form if these yellow flames impinge on cooler surfaces. Here again, carbon monoxide can be produced. Yellow tipping is corrected by the injection of more primary air.

Limits of Flammability:

Upper and lower ranges of gas in the air-gas mixture that will support combustion. Low amount of fuel makes mixture lean. High amount of fuel renders mixture rich.