Ignition inhibiting gas water heater

Details Ignition inhibiting gas water heater Ignition inhibiting gas water heater

2001-03-14

2002-07-16

Wilson, Gregory (Department: 3749)

Liquid heaters and vaporizers

Stand boiler

And condition responsive feature

C122S013010, C122S504000, C122S017100, C126S350200

Reexamination Certificate

active

06418883

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to arrangements to make gas fired water heaters safer for use.
BACKGROUND OF INVENTION
The most commonly used gas-fired water heater is the storage type, generally comprising an assembly of a water tank, a main gas burner to provide heat to the tank, a standing pilot burner to initiate the main burner on demand, an air inlet adjacent the burner near the base of the jacket, an exhaust flue and a jacket to cover these components. Another type of gas-fired water heater is the instantaneous type which has a water flow path through a heat exchanger heated, again, by a main burner initiated from a pilot burner flame. For convenience, the following description is in terms of storage type water heaters but the present invention is not limited to this type. Thus, reference to “water container,” “water containment and flow means,” “means for storing or containing water” and similar such terms includes water tanks, reservoirs, bladders, bags and the like in gas-fired water heaters of the storage type and water flow paths such as pipes, tubes, conduits, heat exchangers and the like in gas-fired water heaters of the instantaneous type.
A particular difficulty with many locations for water heaters is that they are also used for storage of other equipment such as lawn mowers, trimmers, snow blowers and the like. It is a common procedure for such machinery to be refueled in such locations.
There have been a number of reported instances of spilled gasoline and associated fumes being accidently ignited. There are many available ignition sources, such as refrigerators, running engines, electric motors, electric light switches and the like. However, gas water heaters have sometimes been suspected because they often have a pilot flame.
Any vapors from spilt or escaping flammable liquid or gaseous substances in a space in which an ignition source is present, provides a potential for ignition. “Fumes,” “extraneous gases” or “extraneous fumes” is sometimes hereinafter used to encompass gases, vapors or fumes generated by a wide variety of liquid volatile or semi-volatile substances such as gasoline, kerosine, turpentine, alcohols, insect repellent, weed killer, solvents and the like as well as non-liquid substances such as propane, methane, butane and the like. Many inter-related factors influence whether a particular fuel spillage does lead to ignition. These factors include, among other things, the quantity, the nature and physical properties of the particular type of spilt fuel. Also influential is whether air currents in the room, either natural or artificially created, are sufficient to accelerate the spread of fumes, both laterally and in height, from the spillage point to an ignition point yet not so strong as to ventilate such fumes harmlessly, that is, such that air to fuel ratio ranges capable of enabling ignition are not reached given all the surrounding circumstances.
One surrounding circumstance is the relative density of the fumes. When a spilt liquid fuel spreads on a floor, normal evaporation occurs and fumes from the liquid form a mixture with the surrounding air that may, at some time and at some locations, be within the range that will ignite. For example, that range for common gasoline vapor is between 3% and 8% gasoline with air, for butane between 1% and 10%. Such mixtures form and spread by a combination of processes including natural diffusion, forced convection due to air current draughts and by gravitationally affected upward displacement of molecules of one less dense gas or vapor by those of another more dense. Most common fuels stored in households are, as used, either gases with densities relatively close to that of air (eg. propane and butane) or liquids which form fumes having a density close to that of air, (eg. gasoline, which may contain butane and pentane among other components is very typical of such a liquid fuel).
In reconstructions of accidental ignition situations, and when gas water heaters are sometimes suspected and which involved spilt fuels typically used around households, it is reported that the spillage is sometimes at floor level and, it is reasoned, that it spreads outwardly from the spill at first close to floor level. Without appreciable forced mixing, the air/fuel mixture would tend to be at its most flammable levels close to floor level for a longer period before it would slowly diffuse towards the ceiling of the room space. The principal reason for this observation is that the density of fumes typically involved is not greatly dissimilar to that of air. Combined with the tendency of ignitable concentrations of the fumes being at or near floor level is the fact that many gas appliances often have their source of ignition at or near that level.
The present invention aims to substantially lower the probability of ignition in typical fuel spillage circumstances.
SUMMARY OF INVENTION
The invention provides a gas water heater including a water container adapted to be heated by a gas burner; an enclosure surrounding the burner and the water container, the water heater being characterized by having at least one opening adapted to allow air for combustion or extraneous fumes to enter the enclosure without igniting flammable extraneous fumes outside of the enclosure.
Preferably the at least one opening includes an aperture which is covered by a flame trap, which prevents the burner igniting extraneous fumes outside of the enclosure; and an air inlet through which air for combustion purposes is drawn.
Preferably the opening is remote from the gas burner and includes a duct for passage of air to the burner.
Preferably the opening and the aperture are collocated or are a single item.
Preferably the at least one opening is covered by a flame trap.
Preferably the aperture is in the enclosure.
Preferably the aperture is positioned close to a lower end of the enclosure.
Preferably the aperture is positioned in a lower end of the enclosure.
Preferably the aperture is positioned below the burner.
Preferably the aperture is positioned to allow air and fumes outside of the water heater to enter into an air passage leading to the burner.
Preferably the aperture allows air and fumes to enter the lowest point of the air passage.
Preferably one of or a combination of: a light detection or sensitive device; a flame detecting or sensitive device; a temperature sensitive or detecting device; a heat detecting or sensitive device; and an oxygen depletion sensitive or detection device, is located in the water heater to detect flame from the fumes if they have been ignited inside the enclosure.
Preferably the at least one opening includes an air inlet which is not covered by a flame trap, the air inlet having its lowest opening at a height of not less than about 500 millimeters or about 20 inches or more from the bottom of the enclosure.
Preferably the at least one opening is located at or adjacent to the highest point of the enclosure, if the enclosure has a height of about 500 millimeters or greater, from the bottom of the enclosure.
Preferably a snorkel device is provided to extend the at least one opening to a height above the highest point of the enclosure.
Preferably the flame trap includes a heat resistant permeable material having high thermal capacity.
Preferably the flame trap includes a screen selected from either woven or knitted mesh.
Preferably the flame trap is made of metal.
Preferably the flame trap is made of one of: steel, stainless steel, copper and aluminum.
Preferably a lint trap is included to wholly cover the aperture and the flame trap.
Preferably the lint trap is formed by mesh placed in the path of lint or dust to travelling to the flame trap means.
Preferably the water heater includes a gas shut off means which shuts off the gas supply to the burner and or a pilot burner if the air and fumes are ignited after entering the enclosure.
Preferably the gas shut off means includes a heat sensitive means.
Preferably the gas shut off means includes a flame sensitive switch.
Preferably the gas shut off me

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