Thermal safety device for automatically blocking pipes

A thermal safety device is disclosed which, in the area of the closing element, has an uninterrupted circular cross section. Furthermore, the axial guiding of the closing element during the closing stroke is ensured. In the axial continuation of a seat located within the casing there is a guide pin. A closing spring is aligned on this guide pin, and, when taut, the spring is situated as far as possible inside a blind hole, with a throat acting as a control edge, inside the closing element. Under the influence of the closing spring, a ram forming a part of a detecting element, keeps the control edge adjacent to a clip-stop edge when the safety device is in the open position. Once the thermal solder element melts away, however, the resulting change in position of the ram allows the control edge to move away from the click-stop edge, so that the closing element, under the influence of the closing spring, moves into a closed position. The thermal safety device acts to shut off pipes, especially gas pipes, automatically should an inadmissible rise in temperature occur.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention concerns a thermal safety device for automatically blocking 
pipes, especially gas pipes, if an inadmissible rise in temperature should 
occur, in accordance with the characterizing clause of the first patent 
claim. 
Such thermal safety devices, installed in pipes, for example in front of 
gas fittings, gas appliances, gas meters, etc., are available in a variety 
of designs. Their function is to interrupt the gas supply when there is a 
rise in temperature before the temperature on the appliances mentioned 
increases to such an extent that their external sealing is endangered. 
In DE-OS 44 22 241, for instance, a thermal valve safety device is 
described of the type mentioned at the beginning. With this solution there 
is a closing element in the axial continuation of a seat located within 
the casing. This closing element is kept in the open position by at least 
one molding bent approximately into a U-shape. Following a sealing area 
facing towards the seat, on the side facing away from the seat the closing 
element forms a throat, to which a preferably cylindrical collar is 
attached. Both the legs of the molding are therefore located within the 
area of the throat and thus form a rest for the collar against the force 
of the closing spring. Furthermore, the part of the molding which links 
both the legs is propped on a thermal solder element, which is itself 
adjacent to the internal wall of the casing. Once the thermal solder 
element has melted away, the legs of the molding, because the molding has 
consequently changed its position in the casing, are no longer within the 
throat of the closing element. Under the influence of the closing spring 
the closing element thus moves to the closed position. Thereby each of the 
legs forms a guideway directed towards the seat for the collar and/or the 
sealing area of the closing element. 
This solution has the drawback that the casing next to the closing element 
has many fittings, particularly in the circulation cross section of the 
closing element. In order to achieve standard specifications or the flow 
values desired in practice, for example, one is forced to determine the 
dimensions accordingly, and, as a result, similarly required and/or 
desired minimal dimensions, especially for installation, cannot be 
fulfilled. 
Furthermore, in EP-PS 605 551 there is a so-called fire-protection valve 
with a closing spring for automatically shutting off pipes. 
With this fire-protection valve a metallic closing element is aligned in a 
casing. In the sealing area the closing element has a spherical form, with 
which, under the force of a closing spring, it rests in the open position 
on three fixed points formed by two balls and a temperature-sensitive 
component. Both balls, which are themselves propped on a rest in the 
casing, are at such a distance from each other that they form an 
acceptance angle of approx. 90.degree.. Opposite this acceptance angle the 
temperature-sensitive component is secured to the internal wall of the 
casing. 
The component consists of an inwardly-open cup, the base of which is 
secured to the internal wall. The radially inwardly-open cup contains a 
solder element, into which a ball forming a clearance fit with the opening 
of the cup is pressed. The ball forms the third fixed point and is sized 
so that it is located almost entirely within the cup once the solder has 
melted. The three fixed points form the diameter of the rest for the 
metallic closing element, and its dimensions are such that, when the ball 
is in the cup, the closing element is pushed by the force of the closing 
spring through the enlarged opening resulting between the three fixed 
points. 
FIG. 1 accompanying this device demonstrates clearly that the drawback of 
this solution is that the eccentrically positioned closing element is not 
guided axially when the closing stroke is carried out. The force direction 
of the closing spring is never perfectly axial because of the existing 
tolerances, and so in the closing stroke the ball is deflected sideways. 
The inevitably resulting sideways impact, and the centering movement into 
the seat which is therefore necessary, consume part of the kinetic energy 
required to achieve a force fit. Yet this force fit is needed if the 
thermal valve safety device is still to be effective at temperatures where 
the closing spring becomes powerless. 
A similar solution is described in EP-OS 574 677. With this safety gas 
outlet, a retaining ring is positioned within the casing, either in or on 
a rotationally symmetric closing component, the largest external diameter 
of which is only slightly larger than the internal diameter of the 
retaining ring. Here the closing component is pressed by a spring 
component against the retaining ring in the direction of a sealing seat. 
The retaining ring consists of a material that softens at is a 
pre-selected, determined temperature to such an extent that the closing 
component is pushed by the spring component through the retaining ring 
and, in conjunction with a seat, shuts off the gas flow. 
Although with this solution an axial bearing in the open position is 
achieved, because there is no axial guiding of the ball during the closing 
stroke there is nothing to prevent the possibility of a sideways 
deflection of the closing element with the drawback already mentioned in 
the solution described above. 
DE-GM 90 17 534 is another thermal safety device with the same drawback. 
Here a pre-stressed closing cone with a retaining bolt against a 
compression spring is aligned in the casing. Whereas the retaining bolt is 
fixed to the closing cone with its first end, with its second end, the 
diameter of which is enlarged, it is propped on a pyrometric element, 
through the central opening of which the retaining bolt juts. 
A structurally similar device for shutting off pipes, as described in DE-OS 
39 16 100, attempts to counter this drawback by having the retaining bolt 
held centrally by means of a separate guiding element. The disadvantage 
with this is that as well as the extra component, high manufacturing costs 
are involved. In order to assure sufficient guiding the overall dimensions 
are also increased. 
The problem forming the basis of the invention is the development of a 
thermal safety device of the type mentioned, which has an uninterrupted 
circular cross section in the area of the closing element. Furthermore, 
the closing element should be guided axially during the closing stroke. 
The production costs and the overall dimensions should thus be kept as low 
and as small respectively as possible. 
In accordance with the present invention the problem is solved as follows. 
In the axial continuation of a seat located within the casing there is a 
guide pin. On this guide pin a closing spring is aligned, which when taut 
is located as far as possible inside a blind hole drilled in the closing 
element. The blind hole has a throat which serves as a control edge. A 
ram, as part of a detecting element, is on the one side propped on a 
thermal solder adjacent to the internal wall of the casing, and on the 
other side on the external surface of the closing element in the area of 
the control edge, so that the area of the control edge is located 
off-center. When the safety device is in the open position the ram, under 
the influence of the closing spring, keeps the control edge adjacent to a 
click-stop edge. 
Once the thermal solder melts away, on the other hand, the control edge is 
no longer adjacent to the click-stop edge because of the resulting change 
in position of the ram. Consequently, under the influence of the closing 
spring, the closing element takes up the closed position. The guide pin 
then forms a guideway directed towards the seat for the closing spring, 
and this in turn serves as a guide for movement of the closing element. 
A solution has thus been found removing the disadvantage of the background 
art that the casing has many fittings next to the closing element, 
particularly in the circulation cross section of the closing element. What 
particularly makes this solution stand out is its simplicity. 
In order to develop the optimum circulation cross section it is especially 
advantageous if the throat which serves as the control edge is aligned in 
the blind hole on the end of the closing element facing away from the 
seat, and furthermore if the external diameter of the closing element in 
the area of the control edge is substantially smaller than the diameter of 
the seat. 
Other beneficial developments of the invention are indicated in the other 
patent claims. One particular advantage is if the guide pin is formed by a 
metal molding, the surfaces of which run parallel to the casing axis lying 
in the flow direction, and therefore also parallel to the internal wall of 
the casing. Then only a minimum of flow resistance will be generated by 
the metal molding. On the end facing away from the closing element the 
metal molding is connected to the casing, preferably through compression, 
by means of a widening on both sides, whereby the necessary double-sided 
widening forms a bearing shoulder for the closing spring at the same time. 
It is also possible to integrate the click-stop edge into the metal 
molding. 
A particularly good solution is achieved if the click-stop edge is formed 
by the end of the closing spring facing away from the seat. In addition 
the guide pin has at least one recess for the end of the closing spring 
facing away from the seat to click on to. 
For reasons of assembly in particular it is also beneficial if the casing 
has two guide grooves opposite one another to accommodate the widened 
parts of the metal molding, preferably under the conditions of a force 
fit. 
For reasons of flow as well as assembly it is good if the ram is propped 
parallel to its longitudinal axis on one side on the widening of the metal 
molding.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The thermal safety device in accordance with the present invention 
described hereafter, and represented in FIG. 1, has a tubular casing (1) 
with a connection at each of the two ends, each represented in this case 
by an external screw thread (2). Another form of connection is also of 
course possible. Between the two connecting threads (2) the casing (1) has 
an external hexagonal shaped flange (3), which will accommodate a wrench 
or similar tool when the device is installed into a gas pipe, the latter 
not being represented on the diagram. 
In the continuation of the inlet (5) a tubular area (4) is connected in the 
casing (1), which for reasons of flow passes into an extension (6). Here 
the contour of the extension (6) is adapted to the contour of a closing 
element (16), described below in more detail, in order to achieve optimum 
flow. Connected to the extension (6) is the area of the seat (8), aligned 
in front of the outlet (7). In proximity to the tubular area (4) there are 
two guide grooves (9) opposite each other to accommodate the widened parts 
(11) of a metal molding (10), which are pressed into the guide grooves 
(9). It has proved to be advantageous to give the widened parts (11) a 
slight lead-in incline in order to facilitate installation. 
The metal molding (10), with its centrally aligned guide pin (12), juts 
into the extension (6) of the casing (1). As can be seen in FIG. 2, the 
guide pin (12) has on the end facing towards the widened parts (11) a 
recess (13) on one side. This serves to enable one end of a compression 
spring, which functions as a closing spring (14), to click on. The 
function of this as a click-stop edge (24) is described in more detail 
below, whereby the spring end is otherwise propped on a bearing shoulder 
(15) located on each of the widened parts (11). 
In the area of the extension (6) of the casing (1) there is a closing 
element (18), with a spherical sealing area (16) in this embodiment, which 
tapers in an approximately conical form towards the outlet (7), also for 
reasons of flow. Towards the inlet (5) the spherical sealing area (18) 
passes into a neck-shaped area (19), the external diameter of which is 
substantially smaller than the diameter of the seat (8). In the front 
facing towards the inlet (5) the closing element (16) has a blind hole 
(17), which accommodates the closing spring to the largest possible extent 
when it is taut, i.e. in the open position, and in the base of which the 
closing spring, guided by the guide pin (12), is propped. In the immediate 
vicinity of the front the blind hole (17) has a circumferential throat, 
whose function as a control edge (20) is described in more detail below. 
On the external surface of the neck-shaped area (19), in the area of the 
control edge (20), which is located in the zone of contact of the 
click-stop edge (24), the front of a ram (21) of a detecting element is 
propped, which with its other end rests on a thermal solder element (22). 
The thermal solder element (22) is conveniently reposited in a cup (23), 
propped on the interior wall of the casing (1) and thereby partially 
jutting into a guide groove (9). The overall length of the detecting 
element is measured so that by means of the ram (21) the closing element 
(16) in the area of the control edge (20) is located so far off-center 
that the control edge (20), under the force of the closing spring (14), is 
propped on the spring end, which is clicked into position in the recess 
(13) and serves as a click-stop edge (24). 
The action of the thermal safety device in accordance with the present 
invention is as follows: 
Should an inadmissible rise in temperature occur, the thermal solder 
element (22) will melt. Consequently, the ram (21) will, under the force 
of the closing spring (14), be pushed into the cup (23). As a result of 
this change in position of the ram (21), the control edge (20) will slide 
away from the click-stop edge (24) and, by the force of the closing spring 
(14), the closing element (16) will be pushed with its spherical sealing 
area (18) into the seat area (8). 
During the closing stroke the closing element (16) will, by the closing 
spring (14), and this in turn by the guide pin(12), be guided in an axial 
direction, thus avoiding any radial deflections of the closing element 
(16) and the resultant negative effects on the sealing action. 
The thermal safety device in accordance with the present invention is of 
course not simply confined to the embodiment represented here. Changes and 
modifications are possible without departing from the parameters of the 
invention. For instance, the connections with external screw threads can 
also have internal threads or a flange. Furthermore, the spherical sealing 
area (18) can also be designed as a cone, for example. In addition, it is 
also possible to integrate the click-stop edge (24) into the metal molding 
(10).