[0001] The invention concerns a safety device for the control of carbon oxide produced in
a burner.
[0002] It is known that if a fuel bums on air lack, it produces carbon oxide (CO), a very
dangerous toxic gas.
[0003] In order to avoid the carbon oxide formation, it is necessary that the combustion
is always fed by the right quantity of air for a complete combustion, which avoids
or limits within acceptable values the production of carbon oxide.
[0004] On this subject, a new European law on burners requires a stricter control of the
carbon oxide compared to the preceding national laws. It is forbidden to overcome
the fixed limits not only in normal working conditions, that is to say with normal
flow of comburent air, but even when this flow can be reduced for any reason.
[0005] The control is usually made in an indirect manner by a pressure switch, connected
to a pressure tube introduced in the burner, which picks up the absolute pressure
value which changes according to the flow rate of the air and to the air resistance
due to the flowing inside the burner.
[0006] Such resistance considerably changes, either if the flame is absent that is to say
in a pre-ventilation phase of the burner, or if it is present, as it happens during
the working.
[0007] In the first case the pressure is lower than the second one and the pressure switch,
during the pre-ventilation phase monitors a lower pressure than the one monitored
when the flame is ignited, in this case the higher pressure is due to the counter-pressure
coming from the combustion chamber of the boiler.
[0008] That is to say, when the burner begins to work, for a certain period, only the ventilation
works, sending the air to the boiler and washing all the system, so to assure that
at the ignition time there are not smokes and residual gas. In such conditions the
pressure switch P inserted in a downstream position from the fan, as it can be observed
in Fig. 1, shows a pressure which changes according to the air flow rate Q following
the curve A of the diagram: flow rate Q - pressure P, represented in Fig. 2.
[0009] When the burner is ignited, the machine works normally and the pressure switch that,
because of the counter-pressure that is created downstream from the fan as it has
already been said, monitors a greater pressure which, at the flow rate changes, moves
along the curve B represented in the same diagram of Fig. 2.
[0010] In order that the pressure switch works as a safety device and stops the burner working
when the quantity of the produced carbon oxide overcomes the admitted limit, it is
necessary first of all to calibrate the system. This is effected reducing the air
flow rate introduced in the burner till to establish the flow rate value to which
the carbon oxide is produced in a greater quantity than the established limits. The
pressure value corresponding to such flow rate is retained as a calibration reference
value of the pressure switch, the reaching of which the pressure switch must stop
the burner.
[0011] For safety reasons, the pressure switch is then calibrated at slightly greater operating
pressure, so to be sure that the burner stopping happens before reaching the limit
value of carbon oxide generation.
[0012] With reference to the diagram of Fig. 2, the pressure to which the pressure switch
intervenes and that it indicated as control pressure of the pressure switch Pr, must
be lower than both the pressure value of working Pf when the flame is present, and
the value Pp of working in pre-ventilation.
[0013] The system works without inconveniences, if the pressure from which the carbon oxide
is produced in a greater quantity than the one admitted and indicated with Pco, results
lower than the Pr value.
[0014] The problems come up, and this is the application limit of the pressure switch having
only one pipe belonging to the known technique, when the Pco pressure from which the
carbon oxide is generated in a greater measure than the maximum allowed, overcomes,
as it can be observed in Fig. 2, the Pp pressure value of the pre-ventilation working.
In such a case being the control pressure value Pr greater than the pressure value
Pco, the pressure switch would never allow the pre-ventilation working.
[0015] Since obviously, the pre-ventilation working is necessary, in the known technique
as it can be observed in Fig. 2, the pressure switch is always calibrated with Pr
values just a little under the pre-ventilation pressure value Pp and so an accidental
reduction of the flow air during the working can cause the production of carbon oxide
without that the pressure switch can intervene to stop the burner being its calibration
value too low. Substantially the pressure switch intervenes just in case of a drastic
reduction of the air flow rate with a consequent great pressure drop.
[0016] It can be understood that the known technique which considers the use of the pressure
switch with only one pipe as safety device to stop the burner before it produces carbon
oxide in greater quantity than the maximum allowed, presents unacceptable limits according
to the new law.
[0017] JP05157230A and JP05157231A disclose a differential pressure switch detecting the
difference between an inner pressure of a fan case and an inner pressure of a combustion
chamber.
But said devices do not overcome the problems arising from temporary counter-pressure
present in the burner at the lighting time.
[0018] The present invention propose to overcome such limits.
[0019] In particular it is one of the purpose of the invention to realize a safety device
for the control of carbon oxide produced in a burner, where the stop of the burner
is obtained using a pressure signal which results always proportional to the flow
rate of comburent air.
[0020] It is another purpose of the invention to stop the burner before the carbon oxide
overcomes the law limits without interfere with the pre-ventilation conditions.
[0021] Said object is achieved with the realization of a safety device for the control of
the carbon oxide produced in a burner the main features of which are according to
claim 1.
[0022] Preferably, said second pipe is connected with said combustion head but in other
cases it can be connected even with other points downstream from the area where said
conduction pipe is connected with said combustion head.
[0023] According to the invention, a pneumatic shock absorber is placed in series with said
second pipe and consists of a subsiding body having a variable volume which has the
function of putting off the ignition counter-pressure which try to get involved the
pressure switch and so to stop the burner.
[0024] Said purposes and advantages will be stressed during the description of a preferred
embodiment of the invention given as an example but not as a restriction and which
represented in the enclosed drawings wherein:
- Fig. 1 shows a burner provided with a safety device belonging to known technique consisting
of a pressure switch with only one pipe, inserted in the air conduction pipe coming
to the combustion head;
- Fig. 2 shows the curves of the burner of Fig. 1, in pre-ventilation working conditions
in a diagram: flow rate - pressure.
- Fig. 3 shows a burner with a safety device as known from JP 0 515 7230A
- Fig. 4 shows the working curve of the burner of fig. 3 in a diagram: flow rate-pressure;
- Fig. 5 shows the safety device of the invention where it can be observed the inserting
of a pneumatic shock-absorber;
- Fig. 6 shows the detail of the pneumatic shock absorber belonging to a different embodiment
of the safety device of the invention represented in Fig. 5.
[0025] As it can be observed in Fig. 3 a known safety device, indicated as a whole with
1, is applied to a burner indicated as a whole with 2, consisting of a fan 21 which
through a conduction pipe 22 sends a comburent air flow towards the inner of the combustion
head 23.
[0026] Said safety device 1 comprises:
- a pressure switch 11;
- a first pipe 12 which connects said pressure switch 11 to the conduction pipe 22 of
the comburent air coming to the combustion head 23;
- a second pipe 13 which connects said pressure switch 11 to the combustion head 23,
in a point downstream from the area 200 where said combustion head 23 is connected
to the air conduction pipe 22.
[0027] Therefore, the pressure switch 11 is a differential pressure switch which receives
a pressure signal taken from the points 120 and 130 having a different pressure equal
to the pressure gradient that the air flow undergoes between the two pressure points.
[0028] Therefore, such a signal is proportional to the flow itself, independent from the
upstream or downstream absolute pressure that is to say, from the absolute pressure
presents in the pipe 22 and in the combustion chamber 23. In a different embodiment,
not represented, the second pipe 13 can be connected even downstream from said combustion
chamber 23, for example even with the boiler.
[0029] In order to control the carbon oxide , the pressure switch 11 is calibrated with
the lowest value of the working differential pressure of the burner.
[0030] If during the working for a whichever cause, such differential pressure decreases,
the pressure switch changes over the electrical contact with which is supplied, not
represented in the drawing, stopping the burner.
[0031] The lowering of the differential pressure is proportional to the reduction of the
air flow rate and so, the safety device of the invention achieves the first purpose
that is to give a signal proportional to the variation of the flow rate of the comburent
air, unlike the safety devices of the known technique where the signal supplied from
the pressure switch is function of the pressure variation only.
[0032] The working curve of the burner is the curve indicated with 30 represented in the
diagram: flow rate Q - differential pressure ΔP represented in Fig. 4. The curve is
the same, either the burner works with a ignited flame or it works in pre-ventilation,
and this because the measure given by the pressure switch 11 is a differential pressure,
proportional to the air flow rate.
[0033] So, with reference to the Fig. 4, the value of the differential pressure to which
the pressure switch 11 is calibrated and to which the burner is stopped, is pointed
with Pr and it is lower than the differential pressure Pf which is measured during
the working of the burner both in pre-ventilation and with the flame, but it results
greater than the differential pressure Pco in which there is a carbon oxide production
in a greater quantity than the law limits.
[0034] The safety device of the invention intervenes even in the case in which the chimney
should be blocked because of accidental causes. In fact, in such a case, there is
an air reduction flow which allows a reduction of the differential pressure which
causes the burner stop, which should be not possible using a safety device with a
pressure switch with only one pipe, because in case of obstruction of the chimney
it would cause, due to a reduction of the air flow, an increase of the pressure value
which would not cause the involvement of the pressure switch 11.
[0035] The safety device of the invention is represented in Fig. 5 where it can be observed
that the safety device; indicated as a whole with 10, comprises even a pneumatic shock-absorber,
indicated as a whole with 14, represented in the detail of fig. 6, which results connected
in series to the second pipe 130 which connects the pressure switch 110 to the combustion
head 230.
[0036] Substantially, said shock-absorber 14 comprises a bellows made of subsiding material,
for example, plastic material, which presents a side surface 140 formed by a plurality
of concave surfaces 240 joined among them and suited to guarantee to the shock-absorber,
as a whole, the possibility to be subsiding and so to get short and lie down along
the axial direction 141 when its internal volume 340 is interested by a pressure changing.
[0037] The use of said shock-absorber 14 is essential when the temporary counter-pressure
which is developed inner the burner at the ignition time, tends to cancel for an instant
the differential pressure existing at the two ends of the pressure switch 110 because
the counter-pressure at the ignition tends to reverse the polarity of the pre-existing
pressure differential. If this happens, it creates the stop of the burner at the same
moment of the ignition, because of the intervention of the pressure switch.
[0038] In order to avoid such a phenomenon, the pneumatic shock-absorber 14 is inserted
with the function of absorbing, by deformation, the peak of energy due to the ignition
counter-pressure.
[0039] Further, in the inlet and outlet of the shock-absorber 14, the lengths 132 and 131
of the second pipe 130 which connect it respectively to the combustion head 230 and
to the pressure switch 110, are capillary pipes which having a hole of small diameter,
oppose resistance to the flow, reducing the energy. The joining action of the pneumatic
shock-absorber 14 and of the capillary lengths 131 and 132 which form the second pipe
130, damps with efficiency the counter-pressure at the ignition phase allowing the
free working of the system.
[0040] According to what has been described it is understood that the safety device of the
invention, in both the described embodiments achieves all the prefixed purposes. First
of all, it is achieved the purpose to stop the burner only in case of lack of flow
rate that can cause, if the burner does not stop, the production of carbon oxide in
a greater quantity than the one allowed by the law.
[0041] Further it has been seen that the safety device of the invention as it monitors a
differential pressure and not an absolute pressure, makes the control action independently
from the burner operation either if it works in presence of flame, or in pre-ventilation
system.
[0042] Further it has been seen too, that the insert of a suitable pneumatic shock-absorber
allows the absorbing of the ignition counter-pressure which attempt to stop the burner
when this is ignited.
[0043] It is clear that the safety device of the invention can be applied to each kind of
burner, even preferably, its use is expected for gas burner.
[0044] Regarding in particular, the differential pressure switch and the pneumatic shock-absorber,
these could be of whichever type.
[0045] Further, as it has been already said, the pressure switch can be connected with the
conduction pipe of the comburent air or can be in the combustion chamber.
[0046] During manufacturing, further modifications can be made suited to improve the working
device of the invention or to make its construction more economical, meaning that
all said modifications are to be considered protected by the present invention.
1. Sicherheitsvorrichtung (1, 10) für die Kontrolle von in einem Brenner (2) erzeugtem
Kohlenoxid, einen Ventilator (21) umfassend, der über ein Leitungsrohr (22) Verbrennungsluft
in einen Verbrennungskopf (230) schickt, wobei diese Sicherheitsvorrichtung (1, 10)
einen Differential-Druckwächter (110) umfasst, der ein erstes Rohr (12) aufweist,
das an das Leitungsrohr (22) der Verbrennungsluft angeschlossen ist, und ein zweites
Rohr (13), angeschlossen stromabwärts des Bereichs (200), in dem das Leitungsrohr
(22) an den Verbrennungskopf (230) angeschlossen ist, wobei dieser Differential-Druckwächter
(110) mechanisch an eine elektromechanische Vorrichtung angeschlossen ist, die geeignet
ist, den Brenner auszuschalten, wenn der durch den Druckwächter (110) überwachte Differentialdruck
niedriger ist als ein voreingestellter Wert (Pr), dadurch gekennzeichnet, dass ein aus einem nachgebenden Körper mit veränderlichem Volumen bestehender, pneumatischer
Stoßdämpfer (14) in Reihe mit dem zweiten Rohr (130) positioniert ist.
2. Sicherheitsvorrichtung (10) gemäß Patentanspruch 1), dadurch gekennzeichnet, dass dieser nachgebende Körper, der den pneumatischen Stoßdämpfer (14) bildet, ein elastischer
Faltenbalg von im Wesentlichen zylindrischer Form ist, dessen seitliche Oberfläche
(140) durch eine Vielzahl von miteinander verbundenen Austiefungen (240) gebildet
ist, dazu geeignet, den Faltenbalg in axialer Richtung (141) nachgebend zu machen,
wenn sein Innenvolumen (340) einen Druckwechsel erfährt.
3. Sicherheitsvorrichtung (10) gemäß Patentanspruch 1), dadurch gekennzeichnet, dass das zweite Rohr (130) wenigstens eine Länge (131) stromaufwärts vom Stoßdämpfer (14)
und wenigstens eine Länge (132) stromabwärts von demselben Stoßdämpfer (14) aufweist,
gebildet durch eine Kapillarröhre.
4. Sicherheitsvorrichtung (1, 10) gemäß Patentanspruch 1), dadurch gekennzeichnet, dass das zweite Rohr (13, 130) mit dem Verbrennungskopf (23, 230) verbunden ist.
1. Un dispositif de sécurité (1, 10) pour le contrôle de la production d'oxyde de carbone
dans le brûleur (2) comprenant un ventilateur (21) qui, au moyen d'un tuyau transporteur
(22), envoie de l'air comburant dans une tête de combustion (230), ledit dispositif
de sécurité (1, 10) comprenant un pressostat différentiel (110) ayant un premier tuyau
(12) relié au tuyau transporteur (22) de l'air comburant et un deuxième tuyau (13)
relié en aval de la zone (200) où ledit tuyau transporteur (22) est relié à ladite
tête de combustion (230), ledit pressostat différentiel (110) étant relié mécaniquement
à un dispositif électromécanique indiqué pour arrêter ledit brûleur quand la pression
différentielle indiquée par ledit pressostat (110) est inférieure à la valeur préétablie
(Pr), caractérisé en ce qu'un amortisseur pneumatique (14) constitué par un corps s'affaissant ayant un volume
variable est positionné de série par rapport audit deuxième tuyau (130).
2. Un dispositif de sécurité (10) selon la revendication 1), caractérisé en ce que ledit corps s'affaissant qui forme ledit amortisseur pneumatique (14) est un soufflet
élastique ayant une forme essentiellement cylindrique présentant la surface latérale
(140) constituée par une pluralité de concavités (240) unies entre elles, indiquée
pour faire affaisser ledit soufflet selon la direction axiale (141) quand son volume
interne (340) est intéressé par un changement de pression.
3. Un dispositif de sécurité (10) selon la revendication 1), caractérisé en ce que ledit deuxième tuyau (130) présente au moins une longueur (131) en amont dudit amortisseur
(14) et au moins une longueur (132) en aval du même amortisseur (14) constitué par
un tube capillaire.
4. Un dispositif de sécurité (1, 10) selon la revendication 1), caractérisé en ce que ledit deuxième tuyau (13, 130) est relié à ladite tête de combustion (23, 230).