US2744517A - Gas fired heating system - Google Patents

Description

y 8, 1956 G. N. MILES 2,744,517

GAS FIRED HEATING SYSTEM Filed Oct. 20, 1951 lNVENTOR.

Unite GAS FKRED HEATING SYSTEM Application Uctober 20, 1951, Serial No. 252,268

3 Claims. (Cl. 126-110) This invention relates to improvements in heating systems, and particularly to an improved gas supply for a gas fired heating system.

In U. S. Patent 2,579,507 of C. D. MacCracken, there is described a heating system utilizing a combustible gas as a fuel. While not limited thereto, the present invention finds particular application in and will be described herein with special reference to a heating system of the type described in the foregoing copending application.

In practically all gas fired heating systems, the fuel supply line leading to the burner includes a main valve which is usually controlled by a thermostat or the like. Ordinarily, of course, it is anticipated that the control valve will function properly to shut off the gas supply when the valve is closed. However, it is always possible that this valve may fail to close properly, or that it will be open when cooperating parts of the system are inactive, with the result that some gas may flow to the burner when the, system is intended to be shut down, with possible attendant hazards.

In systems of the type described in the above-mentioned copending application, for example, the gas from the main burner normally is ignited by an electrical igniter or spark plug. Of course, when the system is shut down, the igniter Will not be energized. Under such conditions, gas leakage may build up an explosive concentration in the system that could he accidentally ignited withundesirable results. In systems wherein ignition of the gas is by means of a continuously lighted pilot burner, a similar situation may develop if the pilot flame goes out and the main burner valve fails to close tightly.

Aside from the danger of explosion, a leaking main control valve may also result in the seepage of raw gas into the rooms of the house or other enclosure being heated by the system. This is especially true in forced draft systems, and particularly where both combustion and ventilating air are supplied by a common blower as in the system of the above-mentioned copending application. In such systems, when the blower is shut off there is a more or less direct path from the burner back through the air inlet to the ventilating air ducts. Of course, the undesirable features of having raw gas escape into the rooms intended to be heated need not be explained.

It is, therefore, a general object of the present invention to provide an improved fail-safe gas supply for a gas fired heating system. A more specific object of the invention is to provide an improved arrangement for removing from a gas fired heating system any gas that may leak past the main control valve when the latter is intended to be closed. Another object of the invention is to provide a simple, automatic vent valve arrangement for a gas fired heater.

In accordance with the invention, the foregoing and other related objects of the invention are attained by the provision of an automatically valved gas supply control, downstream of the main control valve, that selectively directs gas either to the burner or to a bypass outlet lead- States Patent ing to the furnace flue. In accordance with a preferred embodiment of the invention, the control arrangement includes a Venturi fitting that directs the gas flow in response to the condition of a pressure actuated valve in a venting bypass line.

A more complete understanding of the invention, and of further objects and advantages thereof, can be had by reference to the following description of illustrative embodiments thereof when considered in connection with the accompanying drawing, wherein Fig. 1 is a schematic diagram of a gas fired heating system arranged in accordance with the invention, and

Fig. 2 is a partially schematic and partially cross-sectional diagram showing specific flow control means suitable for use, in accordance with the invention, in the system of Fig. 1.

Referring to Fig. 1 of the drawing, there is shown a gas-fired furnace generally similar to that shown and described in the above-mentioned copending MacCracken application. The furnace of Fig. 1 includes a burner 10 comprising a perforated cylindrical casing 12 defining a combustion chamber 14. A nozzle 22 at the end of a gas supply pipe 23 extends into a mixing tube 24. The mixing tube 24 leads to burner ports 26 in the inlet end of the casing 12. Adjustable air ports 28 may be provided at the inlet end of the mixing tube 24 to admit primary combustion air to the mixing tube, wherein the primary combustion air and gaseous fuel will be thoroughly mixed before passing through the burner ports 26. A spark plug 30 is provided in one wall of the casing 12 for igniting the gaseous fuel mixture.

A blower or fan 18 is provided in an air duct 19 leading to the burner to supply pressurized air both for the burner 10 and for ventilating purposes as explained hereinafter.

A cylindrical sleeve 21 surrounding the casing 12 is spaced therefrom to define a uniform inlet path for secondary combustion air to flow to the combustion chamber 14 through holes 20 in the casing 12. If desired, the mixing tube 24 can be omitted, in which case all of the combustion air will be supplied through the holes 20.

At the outlet end of the combustion chamber 14, heat exchange surfaces 33 of a heat exchanger 34 define a combustion gas passageway 32 leading to an outlet fiue 36.

Part of the pressurized air supplied by the blower 18 will flow through a duct 38 to pass in heat exchange relationship over the surfaces 33 in the heat exchanger and thence out to the space to be heated in the usual manner.

As thus far described, the heating system shown in Fig. 1 is more or less conventional. Certain features of the system should be noted, however, because of their special relation to the present invention.

There will normally be only a very slight draft in the flue 36 when the blower 18 is not operating. Such draft as may exist in the flue will be practically unnoticeable in the combustion chamber 14. Furthermore, when the blower 18 is off, there will be a relatively direct path from the combustion chamber 14 through the holes 21 into the duct 19 and thence through the duct 38 and the heat exchanger 34 into the space to be heated. Therefore, it can be seen that if any gas were to flow into the burner 10 when the blower 18 is not operating, one could not assume that such gas would pass harmlessly out the flue 36. In fact, it is'quite likely that the gas would fiow through the duct 33 and heat exchanger 34 into the space to be heated. If leaking gas did not pass out of the burner, then a concentration of raw gas might well be built up in the combustion chamber 14 that would be explosive.

In accordance with the present invention, provision is made in the gas supply system of the furnace to avoid the foregoing possibilities. As is usual, the supply system includes a gas inlet line 40 having a main control valve 42 therein. The control valve 42 may be any one of a number of different types of valves conventionally used for turning on and off the supply of combustible fuel to the burner. In the present instance, it will be assumed that the valve 42 is electrically operated, under the control of a thermostat (not shown) or the like. On the down-stream side of the control valve 42, a Venturi fitting 74 is provided to direct gas either through the line 23 leading to the gas nozzle 22 or through a bypass line 48 leading to the outlet fiue 36, depending on the setting of a valve 84 in the bypass line. Preferably, the valve 84 is controlled by the pressure in the casing 19, as sensed through a line 100.

As shown, the bypass line 48 can conveniently be connected to the outer hood of the conventional draft diverter 37. This arrangement has the advantage that any condensate forming in the flue 36 due to rapid temperature changes therein will not find its way into the bypass line 48.

One specific arrangement of parts embodying the invention, as shown in Fig. 2, includes a Venturi fitting 74 connected between the down-stream side of the main control valve 42, the feed line 23 and the bypass line 48. The Venturi fitting 74 comprises a casing having an inlet port 76, a first outlet port 78 and a second outlet port 89. A tapered nozzle 82 inside the casing 74 extends from the inlet port 76 to somewhat beyond the second outlet port 80.

in the bypass line 48, there is provided a pressure actuated valve comprising a hollow casing 84 having a diaphragm 86 therein dividing the interior of the casing 84 into upper and lower chambers, 88 and 90, respectively. 1 An inlet port 92 and an outlet port 94 are provided for the upper chamber 88, while a single inlet port 96 is provided for the lower chamber 90. An annular skirt 98 inside the upper chamber 88 surrounds the first inlet port 92 and terminates adjacent the diaphragm 86 to define an internal extension of the inlet port 92 adapted to be closed by the diaphragm 86.

A pipe 100 leads from the lower chamber inlet port 96 to the air duct 19. The outlet port 94 in the upper chamber of the valve communicates with the bypass line 48 leading to the flue 36.

In the operation of the system shown in Figs. 1 and 2, the blower 18 and the main control valve 42 normally will be related in their operation so that there will be a substantial amount of pressure in the duct 19 when the valve 42 is open. Pressurized air in the duct 19 will be communicated by the connecting line 100 to the lower chamber 95* of the pressure actuated valve 84. This pressurized air acting against the large lower face of the diaphragm 86 will be more than adequate to overcome the gas pressure against the relatively small central section of the upper side of the diaphragm 86. Consequently, the diaphragm 36 will seal off the line leading to the bypass 48, and gas will flow from the nozzle 82 downwardly into the feed line 23. However, when the blower 18 is not operating, there will be no pressure in the duct 19 to hold the diaphragm 86 against the skirt 98. Consequently, the diaphragm 86 will move downwardly, opening a path for gas flow through the bypass line 48. Accordin ly, if the main control valve 42 fails to operate properly when the system is shut down, or if there is any gas llow for any reason in the absence of blower pressure, such gas will flow out of the nozzle 82 into the line 78 and through the valve 84 and bypass the line 48 to the outlet fiue 36. This flow of gas will have an aspirating effect which will create a slight suction at the lower outlet port 80 of the Venturi fitting 74. Consequently, it will be impossible for any gas to V flow downwardly through the feed line 23 to the burner,

and in fact any gas in the line 23 when the blower stops operating will be withdrawn and pass out the flue.

From the foregoing, it can be seen that the present invention provides a very simple arrangement for automatically controlling gas input to a gas fired heating system in an efiieient and reliable manner.

What is claimed is:

1. In a heating system of the type utilizing as the fuel a combustible gas and comprising (1) a burner, (2) an outlet flue communicating with said burner to carry away gaseous combustion products therefrom, and (3) a combustible gas supply system including an inlet line and a valve in said inlet line, the improvement which comprises a Venturi fitting comprising (1) a body having an inlet opening communicating with said line on the downstream side of said valve, said body also having two out let openings, one of said outlets being substantially in coaxial alignment with said inlet opening and the other of said outlets being between said inlet and said one outlet and offset from said inlet, and (2) a nozzle inside said body extending from said inlet opening to a point beyond said other outlet, a line connecting said other outlet opening to said burner, a third line connecting said one outlet opening to said fiue, and valve means in said third line for closing and opening said third line, whereby to direct gas passing said first-named valve to said burner when said third line is closed and to said flue when said third line is opened.

2. In a warm air gas-fired furnace of the type comprising (l) a combustible gas burner unit including means defining a combustion chamber, (2) a heat exchanger having surfaces defining a combustion gas passageway in communication with said burner to receive hot combustion products therefrom, (3) an outlet fine communicating with said passageway, (4) a blower communicating with said combustion chamber to supply pressurized air thereto, (5) means communicating with said blower to distribute ventilating air from said blower over said surfaces to heat said ventilating air, (6) a gas inlet line having a valve therein, the improvement which comprises a Venturi fitting comprising (1) a body having an inlet opening communicating with said line on the downstream side of said valve, said body also having two outlet openings, one of said outlets being substantially in coaxial alignment with said inlet opening and the other of said outlets being between said inlet and said one outlet and offset from said inlet, and (2) a nozzle inside said body extending from said inlet opening to a point beyond said other outlet, a line connecting said other outlet opening to said burner, a normally open second valve, a third line connecting said one outlet opening to said flue through said second valve, and means in said sec ond valve communicating with said blower and responsive to pressurized air from said blower to close said normally open valve.

3. In a warm air gas-fired furnace of the type comprising (l) a combustible gas burner unit including means defining a combustion chamber, (2) a heat exchanger having surfaces defining a combustion gas passageway in communication with said burner to receive hot combustion products therefrom, (3) an outlet flue communieating with said passageway, (4) a blower communicating with said combustion chamber to supply pressurized air thereto, (5) means communicating with said blower to distribute ventilating air from said blower over said surfaces to heat said ventilating air, (6) a gas inlet line having a valve therein, the improvement which comprises a Venturi fitting comprising (1) a body having an inlet opening communicating with said line on the downstream side of said valve, said body also having two outlet openings, one of said outlets being substantially in coaxial alignment with said inlet opening and the other of said outlets being between said inlet and said one outlet and offset from said inlet and .(2) a nozzle inside said body extending from said inlet opening to substandaily opposite said other outlet, a line connecting said other outlet opening to said burner, a second valve comprising a hollow body having a diaphragm therein dividing the interior of said body into first and second chambers, said body having therein a first inlet port communieating with said first chamber and a second inlet port communicating with said second chamber, an annular skirt inside said first chamber surrounding said first inlet port and terminating adjacent said diaphragm to define an internal extension of said first port adapted to be closed by said diaphragm, said body further having an outlet port communicating with said first chamber, a line connecting said first port to said one outlet opening, a line connecting said outlet port to said flue, and a line con- 6 meeting said second chamber to said blower to cause said diaphragm to close said first port in response to pressurized air received from said blower.

References Cited in the file of this patent UNITED STATES PATENTS 341,628 Archer May 11, 1886 1,519,673 Doble Dec, 16, 1924 2,062,605 Peters Dec. 1, 1936 2,424,154 Dunham July 15, 1947 2,547,735 Blaha Apr. 3, 1951 2,646,789 Lampert July 28, 1953

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