Damper control apparatus

An apparatus for opening and closing the draft hood discharge opening and vent and fuel line of a fluid fuel-fired heating device such as a domestic water heater. The disclosed apparatus includes a diaphragm-type expansible chamber fluid motor assembly positioned in the burner fuel supply line. The motor assembly is mechanically linked to a damper assembly such that the supply of pressurized fuel acts to actuate the motor for opening the damper assembly prior to the motor assembly admitting fuel to the burner. Additionally, when the supply of fuel is terminated, the motor assembly does not close the damper assembly until after the motor assembly stops fuel to the burner.

BACKGROUND OF THE INVENTION 
The subject invention is directed toward the art of heating apparatus and, 
more particularly, to a vent or stack damper control system for a 
combustion-type heating apparatus. 
The invention is particularly suited for use on gas-fired water heaters and 
will be described with reference thereto; however, the invention is 
capable of broader application and could be used on many different types 
of fluid fuel-fired furnaces, boilers and similar heating devices. 
The typical domestic hot water heater comprises a vertically-extending tank 
with a central vent tube positioned axially thereof. A gas burner is 
positioned beneath the tank and is controlled by a thermostatic valve 
responsive to the temperature of the water within the tank. The water 
within the tank is, of course, heated by the hot combustion products 
impinging against the bottom of the tank and traveling through the vent 
tube. Generally, the exit end of the vent tube is connected through a 
draft hood with a chimney or stack to convey the combustion products to a 
location exterior of the building. 
The general arrangement described above is in widespread use. One of the 
major disadvantages is, however, a comparatively low, overall thermal 
efficiency. For example, during those periods when the burner is not 
firing, natural thermosyphonic action induces a continual flow of air 
through the vent tube and up the stack. This causes thermal losses in 
terms of loss of heated air from the building and cooling of the heated 
water in the tank. The natural cooling of the heated water causes the 
burner to be cycled on-and-off even during periods when no heated water is 
being used. 
Various approaches for overcoming the noted losses have been proposed in 
the prior art. For example, see the following U.S. Pat. Nos.: 
Allman, 1,336,937; 
Stinson, 1,959,970; 
Gilliland, 2,130,491; 
Firehammer, 2,179,120; 
Woods, 2,218,061; 
Stringer, 2,224,705; 
Viola, 2,557,210; 
Hodgins, 3,010,451. 
Generally, the systems shown in the noted patents are unsatisfactory for at 
least one of several reasons. That is, the systems are either complex, 
cumbersome, and expensive and/or they require an electrical supply. In 
addition, the prior systems generally do not provide any means for 
preventing losses due to heated building air entering the draft hood and 
going up the chimney. 
Because of the problems and disadvantages of the prior systems, they have 
generally not been suitable for commercial applications either as original 
equipment or as retrofit units for incorporation in existing equipment. 
BRIEF DESCRIPTION OF THE SUBJECT INVENTION 
The subject invention provides an apparatus which overcomes the problems of 
prior systems and allows both the heating appliance vent pipe or draft 
hood to be closed in coordinated relationship with the operation of the 
burner. In particular, according to one aspect of the invention, a heating 
apparatus of the type having a fluid fuel burner, a vent pipe for 
discharging the products of combustion produced by the burner and a valved 
supply line for supplying pressurized fluid fuel to the burner is provided 
with the improvement which includes at least one damper means movable 
between open and closed positions for controlling flow through the vent 
pipe. An expansible chamber motor means is connected with the damper means 
for moving it to an open position when pressurized fluid is supplied to 
the motor means. Additionally, a connection is provided for depressurizing 
the motor means whenever the valve means is in a closed position. 
Preferably, and in accordance with a further aspect of the invention, means 
are also provided for preventing the flow of fuel to the burner until the 
damper means are in an open position. These means generally comprise a 
valve element operated by the fluid motor after the damper means have been 
moved to an open position. 
OBJECTS OF THE INVENTION 
Accordingly, a primary object of the invention is the provision of a simple 
and reliable apparatus for preventing heat losses from a fluid fuel-fired 
heating apparatus when in a standby mode of operation. 
Another object is the provision of an apparatus of the general type 
described which operates without the need of an electrical power supply. 
Still another object is the provision of a damper control apparatus which 
is comparatively simple in construction and can be installed in new 
equipment or retrofitted to existing equipment. 
Still another object is the provision of an apparatus of the general type 
described wherein the dampers are open well prior to the firing of the 
burner and close slowly after burner operation ceases. 
A still further object of the invention is the provision of a system of the 
type under consideration wherein all power required for operating the 
system is obtained from the pressure of the fuel being supplied to the 
burner.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring in particular to the drawings wherein the showings are for the 
purpose of illustrating a preferred embodiment of the invention only, and 
not for the purpose of limiting same, FIG. 1 shows, in diagrammatic form, 
a comparatively conventional domestic-type hot water heating unit 10 
including a water storage tank unit 12 and a burner assembly 14. The tank 
assembly 12 comprises a generally cylindrical storage tank 16 supported 
from a base 17 and provided with water supply and discharge connections 
not shown. The tank 16 is suitably insulated by insulation 18 covered by a 
sheet metal housing or shell 20. 
Extending vertically through the tank 16 is a vent tube 22 which serves to 
discharge the products of combustion produced by the burner assembly 14 
and, also, to conduct heat to the water within the tank 16. 
The apparatus thus far described is conventional and, as mentioned earlier, 
produces certain inherent thermal inefficiencies. For example, during the 
period when the burner is not firing, the heated water within tank 16 
tends to produce natural thermosyphonic action with respect to the flue 
tube 22. That is, the air column within the flue 22 is heated and rises 
causing a constant flow of air vertically through the flue tending to cool 
the water. Consequently, even though the tank is insulated, a substantial 
heat loss takes place from the water and, as a result, the burner is 
required to periodically cycle on-and-off to maintain the desired water 
temperature even though no hot water is being withdrawn from the tank. 
The subject invention provides a system whereby the heat losses through the 
noted thermosyphonic action can be reduced and substantially eliminated. 
Specifically, as shown, the apparatus includes a discharge plenum or 
chamber 42 positioned at the outlet end of flue 22. A central discharge 
opening 44 is formed in the plenum 42 for permitting the flow of 
combustion products to enter the inlet 46 of a draft hood 48. As is 
customary, the draft hood 48 is connected through an outlet duct 50 with a 
chimney or stack (not shown) for conducting the products of combustion 
exteriorly of the building. According to the subject invention, damper 
means 51 are provided for operation to close off the outlet from the flue 
tube 22, as well as the inlet opening to the draft hood whenever the main 
burner 14 is not operating. While the damper means 51 could take a variety 
of constructions within the scope of the invention, it is specifically 
shown as including a first damper member 52 arranged to move from an 
outlet closing position shown in solid lines to an outlet open position 
shown in phantom. A second damper member 54 is arranged to close the draft 
hood discharge opening and move from the closed or solid-line position to 
the open or phantom position. In the subject embodiment, the dampers 52 
and 54 are positively interconnected by a vertical rod 56. Downward 
movement of the dampers 52 and 54 is limited by rods or stop members 58 
which extend inwardly from the walls of the plenum 42. 
Of particular importance to the subject invention is the arrangement 
whereby the dampers 52, 54 are moved in coordinated relationship with the 
firing of main burner assembly 14. In particular, according to the subject 
invention, an expansible chamber motor means 60 is positioned in the main 
gas supply line 32 between the control valve 40 and the gas burner 24. The 
expansible chamber motor means 60 could have many specific constructions; 
however, the preferred construction is best seen in FIGS. 2 and 3. 
Referring in particular to FIG. 2, it will be noted that the expansible 
chamber motor means 60 preferably includes a lower chamber-defining 
section 64 and an upper section 66. Clamped in sealed relationship between 
housing sections 64 and 66 is a flexible diaphragm member 68 which divides 
the interior of the housing into a sealed lower chamber 70 and an upper 
chamber 72. The housing assembly is connected to the main gas supply line 
32 and enters the lower chamber 70 at an inlet opening 74 and leaves the 
chamber at an outlet opening 76. 
A valve assembly 78 is positioned to control the flow through the outlet 
opening 76. As shown, the valve assembly 78 includes a valve member 80 
carried and guided by a member 82 which extends downwardly and is 
supported from the diaphragm 68. The valve 80 includes an 
upwardly-extending shaft portion 84 which is slidably received in the 
lower wall of the support 82. A stop member 86 is mounted at the upper end 
of the shaft 84 for engagement with the bottom wall of support 82. The 
valve member 80 is maintained under a continual downward bias by a 
comparatively light compression spring 88 positioned between the diaphragm 
68 and the top of stop member 86. 
The diaphragm member 68 is also maintained under a light, continual 
downwardly-directed bias by a compression spring 90 positioned between the 
top housing section 66 and the top surface of the diaphragm 68. 
Additionally, as will be noted, an actuating rod 92 extends upwardly 
through the seal means 62 from the diaphragm 68 into pivotal engagement 
with a lever 94 mounted for rocking movement about a pivot support 96 
carried from the draft hood 48 (see FIG. 1). The right-hand end of the 
lever 94 is pivotally connected to the vertically-extending shaft 56 
between the dampers 52, 54. 
OPERATION OF THE PREFERRED EMBODIMENT 
The operation of the apparatus thus far described will now be explained. 
Assume that valves 30 and 34 are in their normally open position and that 
the pilot burner 26 is operating. When valve 40 is opened, indicating a 
need for operation of the main burner 24, gas enters the lower chamber 70 
of the expansible chamber motor means 60. Upon pressurization of chamber 
70, the diaphragm 68 is actuated upwardly from the dotted-line position of 
FIG. 3. This, of course, causes the actuating rod 92 to move upwardly and 
fully open the dampers 52, 54. It should be noted that until the movement 
of the diaphragm causes support member 82 to lift stop member 86, the 
valve 80 is still seated against the outlet 76. Consequently, the dampers 
are open but no gas can flow through the outlet 76 to the burner 24. 
Continued upward movement of the diaphragm 68 causes the valve 80 to open, 
supplying gas to the burner 24. 
Upon closing of valve 40 (or normally-open valve 30), the supply of gas to 
chamber 70 is discontinued. Consequently, the pressure acting against the 
underside of diaphragm 68 is relieved and the diaphragm moves downwardly 
under the influence of gravity and the compression spring 90. Downward 
movement continues until valve 80 seats against outlet 76 completely 
blocking the flow of gas through outlet 76. At this point, the dampers are 
still in a full open position. However, downward movement of the damper 68 
can continue at a controlled rate by virtue of a bleed line 100 which 
extends from chamber 70 to a vent pilot 102. The rate at which the gas is 
allowed to vent can be varied by changing a flow orifice member 104 
positioned in the vent pilot 102. Additionally, a second small vent line 
106 extends from chamber 72 to pilot 26 to relieve pressure within chamber 
72 and to provide a safe discharge of gas if the diaphragm should rupture. 
The final downward movement of the diaphragm 68 causes the damper members 
52, 54 to move to their final closed positions shown in FIG. 1. 
Because the dampers 52, 54 are closed, there can be no thermosyphonic 
action producing a flow of air through the vent tube 22 to cause cooling 
of the water within the tank 16. Additionally, since the draft hood 48 is 
also closed, building air cannot circulate up the chimney or stack to 
cause additional heat losses. It should be noted that small holes 120, 122 
are provided in dampers 52 and 54 to allow combustion gases from the pilot 
to exhaust when the unit is in standby condition. The holes are, however, 
sized sufficiently small to prevent any substantial heat loss due to 
cooling of the heated water. 
It is important to note that the entire apparatus operates without the 
necessity of a separate electrical power supply or any other outside power 
source. All operation is achieved merely through the pressure of the fluid 
fuel being supplied through line 32. 
While the system has been described with reference to a gas-fired water 
heater, it is, of course, obvious that the invention could equally well be 
applied to any pressurized fluid fuel system on substantially any type of 
heating apparatus including furnaces and the like. 
The invention has been described in great detail sufficient to enable one 
of ordinary skill in the art to make and use the same. Obviously, 
modifications and alterations of the preferred embodiment will occur to 
others upon a reading and understanding of the specification and it is my 
intention to include all such modifications and alterations as part of my 
invention insofar as they come within the scope of the appended claims.