Combustion automatic control system

The invention is with respect to a fail-safe system for stopping damage to water boilers, whose thermostats are not in working order. In an automatic combustion control system of the sort having an elastic thermostat bellows element placed within an outer shell within the water space of a boiler and joined by a chain or the like with the air door for controlling the air inlet rate at some point in the connection between the thermostat element and the door, there is a temperature-sensitive part, for example in the form of a plug of fusible metal or collapsing material, or in the form of a soldered join using a special fusible solder. In one form of the invention, this temperature-sensitive part may take the form of a ring of temperature-sensitive material placed at one end of a spring which is forced together on the temperature increasing. On damage to the thermostat element, the one end of the spring will no longer be supported so that the spring will no longer take effect and so let the air door be moved down under its own weight into the shut position. In a further form of the invention, a body of temperature-sensitive material is placed between a rod, acting on one end of the thermostat element and a turning head which is used for making adjustment in the desired temperature. In a further form of the invention, the temperature-sensitive part takes the form of a plug of temperature-sensitive material between the end of a gripping screw in a jointpiece and a turning rod acted upon by said screw. In a still further form of the invention, the temperature-sensitive part takes the form of a bimetallic wing, which is unhooked from a jointpiece on being heated to a limit temperature. As part of a still further form of the invention, a guide roller for a chain joining the thermostat with the air door is fixed to the side of the boiler by way of fusible solder, this taking the form of the temperature-sensitive part.

BACKGROUND OF THE INVENTION 
The present invention relates to a combustion automatic control system for 
the flow or water temperature of water heaters such as boilers, with an 
expansion thermostat, acted by the water theater temperature, and placed 
in a control system housing, the thermostat being joined up by way of a 
lever linkage or the like in the form of a connection apparatus for 
controlling the position of the air inlet or fire door of the water 
heater, such door being oppositely acted upon by a spring force or by 
gravity. Such combustion automatic control systems have long been used, 
more specially as temperature controllers without any servo effect, for 
boilers and other water heaters fired by solid fuel, for example a boiler 
designed for solid fuel only, such as coke or coal, or one designed for 
two forms of fuel such as coke and oil or coke and gas. In the present 
specification the term "water heater" is used for describing a direct 
central heating boiler or an indirect boiler for producing hot water for 
other purposes than heating, in the home, in trade or in industry in a 
widely different number of designs. Such solid fuel fired water heaters 
have of late started becoming more and more important because of the oil 
shortfall. 
An expansion thermostat placed within the control system housing and worked 
by the thermal expansion of a liquid, by vapor pressure or by gas 
absorption, is, more specially because of the use of an elastic metal 
bellows, as such not very strong in structue and likely to be damaged. The 
motion of the bellows, which is, generally speaking, small in size, is 
stepped up by a lever system or other linkage for producing a large enough 
control motion for driving the draft, air or fire door of the boiler, the 
force of the thermostat working in the opening-direction of the air or 
fire door against gravity, for example the weight of the door itself or 
against the force of a spring or other energy storing unit having the 
tendency of shutting the door. For this reason, a chain, joined with the 
thermostat is kept tight at all times in normal operation. For causing 
opening of the draft or fire door on a change in length of the thermostat, 
the system furthermore has parts producing forces or turning forces 
greater than the force of the door acting on the connection apparatus or 
linkage. Generally, such parts take the form of springs although in the 
past weights have been used as well. More specifically, a combustion 
automatic control system of this sort furthermore has a unit for 
adjustment of the desired temperature value, for example in the form of a 
turning head with a scale placed on the housing of the automatic control 
system and having within it the thermostat, the return spring and the 
linkage. The thermostat is generally placed within an immersed pipe-like 
housing within the water space of the boiler. 
If in the case of such a combustion automatic control system there is a 
trouble condition with respect to the thermostat, for example because of 
its no longer being liquid-tight, it will be decreased in length and go 
into that position which a thermostat in full working order goes into when 
the water is cold. For this reason, the output signal of the thermostat 
seems to be that representative of a low temperature, with the outcome 
that the fire door is opened and this may be responsible for serious 
damage to the boiler if, for example, it is boiled dry. 
SUMMARY OF THE INVENTION 
One purpose of the present invention is that of stopping any such boiler 
damage and other trouble conditions in the heating plant. While it would 
be possible, to make the system safer, to have a second combustion 
automatic control system acted upon by the same temperature, this would be 
responsible for a marked increase in price and generally make the system 
more complex. Furthermore, any such second safety control system might get 
out of order as well, for example if its thermostat is no longer 
liquid-tight. 
For effecting this purpose and further purposes, in the present invention 
in or on the housing of the automatic control system, at a position where 
it is acted upon by the temperature of the boiler, there is a 
temperature-sensitive part which, when its temperature is increased over a 
limit temperature, has the effect of shutting down the automatic control 
of the draft or fire door and causing automatic shutting of the same. 
One useful effect of this system is that it is not only very simple and low 
in price, but may furthermore be used in a safe and trouble-free way, for 
stopping all damage and trouble conditions in connection with the boiler 
and the heating system because the draft or fire door is acted upon by a 
fail-safe system before being in danger of overheating in every case 
automatically so that there is a no chance of an overly high temperature 
being produced. 
It may be seen that the invention makes use in a surprisingly simple way of 
the fact that the automatic control system housing, fixed on or in the 
boiler, and the parts placed therein, have a high-level thermal connection 
with the immersed pipe-like housing of the thermostat within the boiler 
and at the outer face the temperature will be at least generally equal to 
the temperature of the immersed pipe-like housing so that changes in the 
temperature of the last-named will be responsible for nearly equal changes 
in the temperature of the automatic control system housing and the parts 
therein, the function of the system being made better the less the 
difference between the temperature of the control system housing and that 
of the immersed pipe-like housing. By taking certain measures, such as 
heat insulation or by insulating the housing, it is readily possible to 
make certain that the temperature difference between the housing and the 
immersed pipe-like sleeve is kept small enough. Furthermore, a useful 
effect is produced if the housing is made of a material with the highest 
possible thermal conductivity. 
A heating engineer will be able to make use of the general teaching of the 
present invention in a number of different ways. The system may be so 
designed, as part of the invention, that the temperature-sensitive part, 
on being heated to the limit temperature, has the effect of cutting off 
the driving connection between the thermostat and the return spring and, 
in this case, the temprature-sensitive part may take the form of a body, 
as for example one which is melted or is collapsed at the limit 
temperature, taking on a form or position in which it is of no effect at 
the limit temperature. In this respect, the property of certain materials 
is used of melting at low temperatures as for example low melting point 
solders, some sorts of wax or low melting point salts. Furthermore, it is, 
however, possible for the collapsing body to take the form of a bottle of 
glass or other brittle material filled with a liquid undergoing expansion 
on an increase in temperature. On getting to the limit temperature, the 
bottle will then be burst, that is to say collapsed, and have no further 
effect as part of the connection apparatus. In the combustion automatic 
control system, the temperature-sensitive part may, for example take the 
form of a support for at least one end of a return spring housed in the 
housing of the automatic control system. 
In the case of a further working example of the invention, the driving 
connection between the fire door and the thermostat may be shut down with 
the help of a temperature-sensitive coupling which, as part of a further 
development of the invention of good effect, may take the form of a design 
in which a driving ear, drivingly joined with a jointpiece journalled in 
the housing of the automatic control system, has a tailpiece which is 
soldered to the outer face of the thermostat casing. 
Furthermore, as part of the invention, it is possible for the 
temperature-sensitive part to be in the form of a bimetallic wing, placed 
between the thermostat and the draft or fire door and having the function 
of cutting off the driving connection when the temperature is increased. 
These forms of the invention noted so far do, however, make necessary a 
special design of the thermostat for automatic control. However, the same 
effects may be produced with the help of a combustion automatic control 
system of any design, this being made possible in the invention if the 
temperature sensitive part is within the path of the power or driving 
connection joining the connection apparatus or lever system of the 
automatic control thermostat with the draft or fire door of the boiler or 
water heater. In this way it is possible for any desired automatic control 
thermostat or combustion automatic controller to be used as part of the 
invention. 
As part of a preferred form of the invention, the connection part, for 
example a chain, joining the connection apparatus of the automatic control 
thermostat with the draft or fire door of the boiler, is kept pulled tight 
in its position of operation by a temperature-sensitive part which is 
placed at a position of the boiler acted upon by the temperature produced. 
This system may be very simply designed by having the chain or the like 
running over guide roller, whose support is fixed to the boiler so as to 
make up the pressure-sensitive part and, for doing this, it is possible 
for a base-plate of the support of the guide roller to be fixed to the 
wall of the boiler by a safety solder or fusible metal or the like.

DETAILED ACCOUNT OF WORKING EXAMPLES OF THE INVENTION 
Firstly, the general design of a combustion automatic control system 
according to FIGS. 1 to 5 will be described. This control system is only 
as taken to be an example and as the starting point for a number of 
different working examples of the invention fully detailed below are some 
of the possible forms of the invention for producing the invention's 
useful effects. 
In the present example of a combustion control system a generally pipe-like 
thermostat 2 is positioned in an immersed casing 1 so that, in operation, 
the thermostat's temperature increases to the temperature of the flow 
water heated by the boiler. A pin 4, fixed to the lower end of a metal 
bellows 3 extends outwardly of the thermostat 2 which comprises an outer 
shell, a spring plate 12 affixed to the upper end of the shell, sealed 
bellows 3 within the shell and an expansion liquid L within the 
liquid-tight space between the bellows and the shell. Pin 4 rests against 
a turning head 5 (for adjustment of the desired water temperature) which 
is preferably of thermally insulating material, and has temperature scales 
for an upright and for a horizontal position of the control system. The 
part of the system including the thermostat 2 and the pin 4 is forced by a 
spring 6 against a bearing in turning head 5 without interfering with the 
turning of the head by hand. The thermostat 2 is connected with a 
jointpiece in which a lever rod 8 , having an angled lever arm 8', is 
fixed by means of a set screw 11. At the free end of the lever arm 8' a 
chain 9 is fixed, whose lower end is hooked into an eye on draft door 10 
on the firebox door of the boiler 111 (FIGS. 3 or 4). Such a combustion 
automatic control system may be disposed in an upright (FIG. 3) or in a 
horizontal position (FIG. 4) depending on the design of the boiler. For 
connecting the thermostat 2 with the jointpiece 7, an upwardly extending 
driving ear 13 is provided and is connected with a top spring plate 12 of 
thermostat 2, the ear 13 having a design for example as in FIG. 17 in the 
form of a double cross, whose cross-arms are disposed loosely beneath a 
nose 14 defined by a cutout of the jointpiece 7. The immersed casing 1, in 
which thermostat 2 is placed so that it may be taken out if a new 
thermostat is needed, is for avoiding damage to the boiler if there is any 
loss of liquid from the thermostate. Casing 1 is fixed in a threaded 
collar 28, having a male thread 29 engaging a female thread in the boiler 
wall. An automatic control system housing 30 is fixed on threaded collar 
28 for extending outwardly of the boiler, turning head 5 being threaded on 
to its top end. 
The spring 6 is so stiff in design that the weight of the draft door 10 in 
the firebox door of the boiler is not responsible for any change in 
position of the parts of the automatic control system. If now the 
temperature of the water in the boiler increases for example, there will 
be an expansion of the liquid within the thermostat 2, thus decreasing the 
length of the bellows 3 of the thermostat. Because the plate at the lower 
end of the bellows is prevented from moving upwardly by rod 4, spring 
plate 12 is forced downwardly thereby compressing spring 6, making it 
possible for jointpiece 7 to be turned downwardly together with the angled 
arm 8' of lever rod 8, lever rod 8 being rotated clockwise when viewed in 
FIG. 5 (as its arm 8' is pulled downwardly) as caused by the weight of the 
air floor 10. For this reason, the door will be shut somewhat further, 
thus decreasing the draft so that the desired boiler temperature is 
produced. If the boiler temperature decreases below the desired 
temperature, the liquid within the thermostat 2 will occupy less space so 
that now, by the force of spring 6, plate 12 will be moved upwardly 
turning lever rod 8 about its axis in a counterclockwise direction and, by 
way of lever arm 8' and chain 9, the air door 10 is opened somewhat 
farther, this causing the boiler temperature to be increased. For 
adjustment to obtain a different water temperature head 5 for adjustment 
of the desired temperature is turned and if, for example, because of a 
lower outside temperature, a higher boiler temperature is desired, turning 
head 5 is turned to effect movement of the thermostat 2 and the pin 4 in 
an upward direction. Thus, draft door 10 is opened somewhat farther so 
that its upward and downward movements in response to changes in 
temperature will increase relative to a somewhat higher point pertaining 
to the higher temperature desired. 
In the case of any trouble condition in the automatic control system, 
because, for example, of loss of liquid from thermostat 2 resulting in an 
extreme increase in the boiler temperature, precautions must be taken to 
assure that, nevertheless, the draft door 10 of the boiler is 
automatically closed and, for this purpose, as part of the invention, the 
driving connection between the automatic control system and the air door 
of the boiler is cut off in such a way that the desired automatic shutting 
of the air door takes place under its own weight or, if desired, because 
of some other effect. This teaching may be put into effect in a number of 
different ways. 
In the example according to FIGS. 6 and 7 there is, between the top spring 
plate 12, connected with the thermostat 2 and top end of the return spring 
6, a temperature-sensitive element 15 against which the top end of the 
spring rests within the system housing. Element 15 is said to be 
temperature-sensitive in the sense that it is fused or collapsed at a 
limit temperature. In the case of the further development of the invention 
according to FIGS. 8 and 9, the temperature-sensitive element 15 is 
disposed between the lower end of return spring 6 and an inwardly 
extending lip of threaded collar 28, which would otherwise have this 
spring resting against it. If desired, it would be possible to have two 
such temperature-sensitive elements 15, one at the top (as in FIGS. 6 and 
7) and one at the lower end of the spring (as in FIGS. 8 and 9). Because 
the system housing 30, the threaded collar 28 and the spring 6 generally 
elevate to the full temperature of the boiler, the temperature-sensitive 
element 15 will be melted or collapsed on approaching the limit 
temperature and will then yield so that the force of spring 6 will 
decrease to zero or near zero and the system will be overpowered by draft 
door 10 so that the same will be automatically shut. 
In FIGS. 10 and 11, the turning head 5 of the automatic control system has 
within it a temperature-sensitive element 18, which may be melted or burst 
at an extreme temperature, having the top end 4' of pin 4 resting against 
it, end 4' extending into only a portion of a hole 17 in the hollow guide 
16. Element 18 lies in the space in the hole over the end pin 4' and, 
because it contacts pin end 4', maintains the same temperature as the 
boiler or a temperature only slightly less than the temperature of 
immersed casing 1. However, the temperature of the temperature-sensitive 
element will be high enough, that is to say near enough to the boiler 
temperature, for the element to be melted or collapsed if there is any 
danger of an excessive temperature. Pin 4 will then no longer be 
supported, that is to say pushed downwardly, spring 6 then forcing spring 
metal bellows 3 together with the driving ear 13 and the right hand part 
of jointpiece 7 so far in an upward direction that the driving ear 13 is 
unhooked from nosepiece 14 (which is made short enough for this to occur) 
of jointpiece 7, and once this occurs, jointpiece 7 will drop downwardly, 
the weight of draft door 10 causing a turning of lever rod 8, and draft 
door 10 being shut. 
A further working example for effecting the purpose of the invention, that 
is to say stopping the driving connection between the automatic control 
system and the air door on overheating of the boiler, is so designed that 
the driving connection between the jointpiece 7 and the lever arm 8 is 
overcome, or, in other words, lever arm 8 is disconnected from jointpiece 
7. In FIGS. 12 and 13, this is effected by placing between the end of 
screw 11, screwed into a threaded hole 19 in jointpiece 7, and the, for 
example, six-sided outer face of lever rod 8, a temperature-sensitive 
element 20 which is melted or collapsed when overheated. Heating of this 
element is more specially by way of the jointpiece 7, when the boiler is 
overheated so that it soon gets to a temperature at which it is melted or 
collapsed. Then lever rod 8 is able to be freely turned and is in fact so 
turned under the effect of the weight of draft door 10 which accordingly 
closes. 
FIGS. 14 and 15 of the drawing are views of an especially useful and very 
trouble-free working example of the invention, in which case the driving 
ear 13' is not fixed to the spring plate 12' of thermostat 2, but has a 
tailpiece 21 extending through an opening 23 in spring plate 12', under 
which tailpiece 21 is soldered as at 22 (FIG. 15) to the outer face of 
thermostat 2. For producing a better supporting effect, the ear tailpiece 
21 may extend beneath spring plate 12' in the form of a collar 24 or cuff 
surrounding the thermostat 2, on which it is fixed by fusible solder 22. 
Normally the driving ear 13' is moved together with the thermostat 2 with 
which it is joined and has its effect on jointpiece 7. If, however, 
because of a trouble condition of the thermostat, there is overheating, 
the increasing temperature of the automatic control system housing will 
have the effect of melting the fusible solder 22, spring 6 then no longer 
producing any force acting against jointpiece 7, the weight of draft door 
10 now forcing the door downwardly into its closed position. 
In FIGS. 16 and 17, use is made of a bimetallic connection and for this 
purpose a form of system, for example of the type noted, may have the 
driving ear taking effect on the jointpiece 7, may be in the form of a 
bimetallic wing 25 (FIG. 17), whose lower foot part 27 takes the form of 
the spring plate fixedly joined to the thermostat 2. If now the 
temperature in the automatic control system becomes greater than the limit 
temperature, the bimetallic wing 25 will be bent into a position 25' shown 
in phantom outline in FIG. 16, the cross-arms 26 (FIG. 17) then clearing 
nosepiece 14 of the jointpiece 7. The housing 30 of the automatic control 
system may be hollowed out at 31 for accommodating movement of the 
bimetallic wing between its positions 25 and 25'. By operation of the 
bimetallic wing, the driving connection between the jointpiece 7 and the 
thermostat 2 is cut off. In this case spring 6 will not be responsible for 
any torque or turning force acting on lever arm 8' so that the connection 
apparatus will become loose and the door 10 will be moved down by its own 
weight into its closed position. 
In FIGS. 18 to 20, the chain 9 (or a cord) is guided over a guide roller 32 
having a groove and which is journalled on a pin 33 in a roller support 
34. This support and its base plate 35 is fixed (FIG. 19) by a fusible 
solder 36 directly on a wall face 37 of hot water boiler 111. 
If now the boiler is overheated, melting fusible solder 36, bearing support 
34 with guide roller 32 will be disconnected from the outer face 37 of the 
boiler and dropped therefrom. The pulling force of chain 9 will now 
decrease to zero, the acting length of the chain being accordingly 
increased so that the air door 10 will be automatically shut. Chain 9 will 
then be moved out of the pulled-tight position shown in solid outline into 
its loose position 9' shown in phantom outline. 
As will be seen from the further development of FIG. 20, it may be suitable 
for the base plate 35 not to be soldered onto the outer face of the boiler 
wall itself, but to make use of an interposed plate 38 which is fixed to 
the boiler wall 37, for example by welding. In this case the fusible 
solder 36 will be between this plate 38 and the base plate 35 of bearing 
support 34 for roller 32. 
The forms of the invention as herein above described are as taken to be 
examples of good effect, but which, however, do not have a limiting effect 
on the field covered by the invention, the same in fact covering all other 
further developments and changes therein inasfar as they put into effect 
the principle teachings of the invention. As an example, a thermo-element 
may be used in the invention, whose hot junction is on or in the housing 
of the combustion automatic control system while the cold junction is at 
some distance from the combustion automatic control system on the boiler 
and will be at a temperature equal to the air temperature within the 
boiler room. 
The thermal emf then produced between the two soldered joints may them, 
acting through an electromagnet or the like, have the effect of 
unclutching a coupling in the automatic control system housing, in the 
case of boiler overheating, so that the draft air door of the firebox goes 
back into its shut position.