NOZZLE UNIT FOR OIL BURNER

Description

[0001] The invention relates to a nozzle unit for atomizing pressurized oil in an oil burner. The nozzle unit comprises a nozzle holder with an inner cylindrical space, a nozzle fixed in the nozzle holder and a pressure dependent valve housed in a valve unit. Such a unit is e.g. known from US 500 230 A.

[0002] DE 38 14 530 C1 describes an oil burner with a pressure dependent valve between oil preheater and nozzle. The purpose of the valve is to prevent dripping from the nozzle in the standstill periods of the burner.

[0003] DE 39 01 032 C1 describes a nozzle with a built-in pressure dependent valve. When the pump starts, the valve opens, but only when the pump has obtained sufficient pressure for a ball to compress a spring. Correspondingly, the spring presses the ball against the seat as soon as the pump speed reduces.

[0004] The pressure dependent valve is efficiently preventing dripping from the nozzle, both when the burner stops and heat radiation heats up the nozzle holder, and during start-up, while the oil preheater heats the oil. However, the valve must be replaced simultaneously with the nozzle which is normally replaced once a year. The life of the pressure dependent valve is much longer, but it is scrapped together with the nozzle.

[0005] From DE 32 26 023 it is also known to place a valve between preheater and nozzle. Further, there is a bypass connection from the oil preheater to the low pressure side of the pump. The bypass connection also comprises a manually controllable flow restriction enabling the setting of the amount of oil flowing through the bypass connection at a value at which the pump can maintain an optimum nozzle pressure.

[0006] Thus the problem with heating of oil in the preheater is solved in that the bypass connection diverts pressure when the pump is without pressure, and in the pressureless state the valve between preheater and nozzle is closed by a spring pressing the valve closing element against the valve seat. However, the valve is fixed in the nozzle holder and cannot adapt to different nozzle lengths. In front of the valve a volume will be exposed to heat radiation when the burner stops, and the volume expansion can lead to oil dripping in the burning chamber. A large volume before the oil preheater leads to bad combustion at the start, as the oil is cold.

[0007] It is the purpose of the invention is to enable the use of standard nozzles and to prevent unnecessary replacement of the pressure dependent valve while leaving the oil volume between valve and nozzle approximately unchanged.

[0008] In accordance with claim 1 this task is solved by arranging the valve unit in the cylindrical space of the nozzle holder, so that it will be pressed by the pressurized oil to abut against the nozzle or a nozzle filter on the downstream side, while no parts of the nozzle unit abut against the valve unit on the upstream side.

[0009] This enables replacement of the nozzle without requiring simultaneous replacement of the valve unit. At the same time the valve unit will prevent leakage of oil at nozzle replacement. Since the valve unit is pressed against the nozzle or the nozzle filter by the oil pressure the valve will automatically reduce the volume between nozzle and valve unit, independently of the total length of the nozzle.

[0010] The pressure dependent valve incorporated in the valve unit could be a ball valve. The ball is pressed against a seat by a pressure spring while the pump pressure acts in the opposite direction. This will result in a rigid valve, opening fast when the pressure force on the ball exceeds the spring force.

[0011] In a preferred embodiment of the invention the pressure dependent valve being part of the valve unit has a valve seat co-operating with a closing member in the shape of a diaphragm. The pressurized oil forces the diaphragm in the opening direction, and a piston biased by a resilient element forces on the diaphragm against the valve seat. This will result in a valve in which a predetermined opening pressure is required to open the valve, and the valve causes a minimum pressure drop when open. Thus, the nozzle mounted after the valve can utilise almost all the pressure supplied by a pump.

[0012] When the valve unit according to claim 4 is in the closed valve state, the oil pressure can act on the diaphragm in the opening direction on a ring shaped area extending around the valve seat whereas the whole diaphragm surface facing the valve seat is acted on by the pressurized oil and pressed against the piston in the open valve state. Thus, in the closed state, the oil pressure can act on a limited area of the diaphragm, thereby securing that the valve does not open until a predetermined pressure value is exceeded. When this pressure value is exceeded and the valve opens, the nozzle will act as flow limitation, and the pressure increases. The increasing pressure influences the whole diaphragm surface, and the diaphragm presses the counter pressure piston back. Thus the pressure drop across the valve decreases to a very low value.

[0013] The valve unit comprises a cylinder-shaped housing and a cup shaped cylinder. The cylinder-shaped housing has a radial channel connecting a circumferential channel on the housing with a ring shaped channel facing the ring shaped area. The housing is provided with a passage connecting the circumferential channel with the inlet. A cup shaped cylinder is fixed to the cylinder-shaped housing. The cup shaped cylinder contains a spring and a piston, and the diaphragm is fixed between the cylinder-shaped housing and the hollow cylinder. The valve unit is easy to replace, if faults should occur, or to clean during service. Furthermore, the passage will form a filter stopping large particles which might otherwise disturb the valve function.

[0014] The passage permitting oil to flow to the circumferential channel can be made by forming at least one channelon one side of the cylinder shaped housing or the surface of the cylindrical space.

[0015] The valve unit can be made by having a cylinder-shaped housing with an external diameter permitting oil passage between valve housing and the surrounding cylindrical space. As there is a ring shaped passage extending around the cylinder-shaped housing, an offset resting against the surrounding cylinder cannot act as a blocking as this will cause an increased clearance on the opposite side.

[0016] The nozzle can be sealed towards the nozzle holder by means of a sealing ring fixed on the nozzle. The sealing ring seals against a ring shaped shoulder in the nozzle holder. This moves the sealing to the front edge of the nozzle thread, and air in the thread between nozzle and nozzle holder will cause no trouble, and means for air relief will not be required. If, at the same time, the nozzle holder comprises the present ring shaped shoulder for sealing, standard nozzles can be used, however without the sealing ring and the advantages it offers.

[0017] Advantageously, the pressure dependent valve can be mounted in a nozzle holder mounted in the normal oil preheater outlet. This will enable mounting of the pressure controlled valve in an existing oil preheater.

[0018] In the following the invention is explained on the basis of drawings, showing:

Fig. 1

A section through a nozzle holder

Fig. 2

A section through a second nozzle holder

Fig. 3

A section through an embodiment of the invention

Fig. 4

A section through a preferred possible embodiment

Fig. 5

An enlarged section of the displaceable valve unit from fig. 4 in a closed state

Fig. 6

Same section as fig. 5, however, the valve is in an open state.

[0019] Fig. 1 shows a nozzle unit 1 for an oil burner, comprising a nozzle 2 and an oil preheater 3. The oil preheater 3 is only shown schematically by a section line through a possible oil preheater which is assumed to be commonly known. The oil preheater 3 is mounted in a housing 4, into which the nozzle 2 with its filter 5 is screwed by means of a thread 6. The nozzle 2 has a sealing surface 7 fixed against a plane surface on the housing 4 by means of the thread 6. This gives a sealing for the oil. Between oil preheater 3 and nozzle filter 5 there is a pressure dependent valve 8, consisting of a ball 9 co-operating with a seat 10. The ball 9 is influenced in the closing direction by a spring 11, controlled by a spring guide 12, by which the spring 11 will rest against a spring stop 13. The valve 8 is fixed in the housing 4 by a thread 14, and the sealing between housing 4 and the pressure dependent valve 8 is made by an O-ring 15, sealing against a surface on housing 4. A pre-filter 16 is mounted before valve seat 10, and 17 is an O-ring sealing between the inner components of the oil preheater and the housing 4.

[0020] When starting a burner, a pump (not shown) will build up a pressure, and after a certain preheating time a solenoid valve in the oil pump will release pressure to the nozzle string. However, the ball valve 9 requires a high pressure before opening, as the active pressure area of the ball 9 is very restricted. The pressure dependent valve 8 opens suddenly, and the active pressure area increases suddenly when a flow occurs around the ball 9. Thus oil under high pressure is suddenly released to the oil nozzle 2, in which atomizing takes place by means of a swirl chamber. When the burner is turned off, the pressure supply is disconnected in that a solenoid valve in the pump is closed, and as soon as the pressure reduces, the spring 11 presses the ball 9 against the valve seat 10, and the valve closes.

[0021] Fig. 2 shows an alternative nozzle holder in which the pressure dependent valve 8 is arranged in a nozzle holder 18 mounted in the outlet of the oil preheater 3. Here, the pressure dependent valve 8 is fixed in the nozzle holder in a thread 21, together with a pre-filter 19. The pressure dependent valve 8 seals against the nozzle holder 18 by means of an O-ring 22.

[0022] Sealing between nozzle 2 and nozzle holder 18 is here made by a clamping ring 23. The clamping ring is fixed around the nozzle filter 5 before mounting the nozzle. Before the thread is screwed home, there will be contact on surface 24 between the nozzle and the clamping ring 23 and on surface 25 between the clamping ring 23 and the nozzle holder 18. Clamping between the surfaces will prevent oil from reaching the thread 6. The sealing surface 7 of the nozzle 2 is now unused, and the drawing shows that there is a distance to the normal sealing surface of the nozzle holder. This causes that oil has no access to the thread 6, and air bubbles cannot arise in the thread, so means for air relief of this thread is not required.

[0023] Fig. 3 shows a section through a first embodiment of the invention. Like fig. 1 and 2, fig. 3 shows a nozzle 2 and an oil preheater 3 between which a pressure dependent valve 8 is arranged. The design of the pressure dependent valve 8 is described above. The invention in fig. 3 differs from fig. 1 in that the pressure dependent valve 8 is housed in a valve unit 50 comprising, besides the pressure dependent valve 8, a piston shaped unit 28, a flanged sleeve 32 and a prefilter 30. The valve unit 50 is placed displaceable in a cylindrical space 27. The pressure dependent valve 8 is mounted in the piston-shaped unit 28 The sealing between the piston-shaped unit 28 and the surface of the cylindrical space 27 is made by an O-ring 34. A sealing O-ring 33 is placed between the pressure dependent valve 8 and the piston unit 28. The flanged sleeve 31 fixes the valve 8 together with the pre-filter 30 and a socket 32 for fixing. Fig. 3 also shows the sealing ring 23 mentioned under fig. 2.

[0024] The valve unit 50 is displaceable in the cylindrical space 27, and therefore the first pressurizing of the system will cause the oil pressure to push the valve unit 50 to rest against the nozzle filter 5. This rest remains until the nozzle is replaced. If then a nozzle 2 is mounted which has a longer filter 5 than the previous nozzle 2, the valve unit 50 will be displaced backwards towards the oil preheater 3. If a nozzle 2 with a shorter filter 5 is mounted, the oil pressure will displace the valve unit 50 forward to secure rest against the filter 5. Thus, there is always a minimum of oil between valve unit 50 and nozzle 2. The displaceable mounting of the valve unit 50 also facilitates replacement of the whole valve unit 50 during service, which may be preferred at certain long intervals, as the pre-filter 30 also requires replacement.

[0025] Compared with fig. 3, fig. 4 shows an alternative embodiment where instead of the previously shown ball valve a diaphragm valve is used in the valve unit 50. The fig. shows a nozzle holder 26 in which is mounted a nozzle 2 with a nozzle filter 5. The nozzle is fixed in a thread 6, and a ring shaped sealing element 23 is fixed against the nozzle by means of a sleeve 24 and rest against the nozzle holder on a surface 25. This gives direct sealing against the nozzle filter 5, so that oil is prevented from reaching the thread 6. Thus an air pocket cannot occur in the thread, where it is compressed under pressure, and which re-expands when the burner is stopped and thereby oil is pressed out through the nozzle. The valve unit 50 is also like in the previous embodiment arranged displaceably in the cylindrical space 27. The valve unit 50 comprises a cylindrical housing 35 and a cup shaped cylinder 36. The valve housing 35 is connected with the cup shaped cylinder 36, and between the housing 35 and cylinder 36 a diaphragm 37 is fixed which rests against a valve seat 38. A piston 39, pressed by a resilient element 40, presses the diaphragm 37 to rest against the valve seat 38. The diaphragm 37 is influenced in the opening direction by the oil pressure applied through a channel (shown in fig. 4a) along the outside of the valve unit 50. This channel is in connection with a radial channel 42 which again is in connection with a ring shaped channel 41, in which the pressurized oil presses against the diaphragm. The valve seat 38 has a central opening which is connected with the nozzle filter 5 in its central area and with the outside of the nozzle filter 5 through at least one radial channel 43. The assembling of the displaceable valve unit 50 takes place by means of an edge 44 on the valve body 35, which is flanged around an edge on the cup shaped cylinder 36. Leakage along the cylinder shaped housing 35 is prevented by an O-ring 46 arranged in a groove in the cylinder-shaped housing 35.

[0026] Fig. 4a shows an enlarged section of fig. 4 in which an oil channel 45 is connected with a circumferential channel 47, which again is connected with the radial channel 42. The channel 45 can be made as one or more tracks, either in the valve housing 35 or internally in the cylindrical space 27. An alternative solution could be to make the valve housing 35 with a smaller diameter than the cylinder 27. This would give an oil passage, which is independent of a possible offset placing of the valve housing 35. There will always be an open passage. Channel or passage 45 will act as an oil filter, as all large impurities in the oil will be stopped before having any influence on the valve function.

[0027] Fig. 5 and fig. 6 show an enlarged section of the valve unit 50. Fig. 5 shows the valve unit 50 in the closed state, and in fig. 6 the valve unit 50 is shown in the opened state. In the closed state in fig. 5 the diaphragm 37 is pressed against the valve seat 38 by the piston 39 which is again pressed by a spring 40 to rest against the valve seat 38. The opening pressure for the opening of the valve unit 50 can only influence the ring shaped area of the channel 41. This means that a relatively high pressure is required for the diaphragm 37 to exert sufficient pressure against the piston 39 to compress the spring 40. When, however, the opening starts, i.e. a small oil flow runs from the radial track 42 to the ring channel 41 across the valve seat 38 to one of the two outlets, channel 43 or the direct way to the nozzle filter, the nozzle will act as a flow restriction, and the pressure behind the valve seat will start increasing. From fig. 6 it can be seen in the open state of the valve unit 50, how the whole diaphragm surface is exposed to oil pressure, as the flow restriction taking place over the valve seat 38 is very small compared with the opening area of the nozzle. This gives the valve unit 50 with a very small pressure drop when the valve is open.

[0028] The invention can be used with a large number of different oil burners. A possible embodiment of an oil burner has separate pump and fan. Thus pre-ventilation of a burning chamber can take place when the pump is not rotating. Thus the solenoid valve in the pump or in front of the nozzle is not required. At pump standstill oil can be pressed back through the pump, and thus an oil preheater can be used without requiring any valves other than the one mentioned in the invention.

[0029] Advantageously, the pump can also be used in oil heating plant with oil preheater, where a solenoid valve is available in the pump and where a bypass is provided for pressure release of the nozzle string.

Claims

1. Nozzle unit (1) for atomizing pressurized oil in an oil burner, the nozzle unit (1) comprising a nozzle holder (26) having an inner cylindrical space (27), a nozzle (2) fixed in the nozzle holder (26) and a pressure dependent valve (8) housed in a valve unit (50), characterised in that the valve unit (50) is arranged in the cylindrical space (27) of the nozzle holder (26), so that it will be pressed by the pressurized oil to abut against the nozzle (2) or a nozzle filter (5) on the downstream side, while no parts of the nozzle unit (1) abut against the valve unit (50) on the upstream side.

2. Nozzle unit according to claim 1, characterised in that the pressure dependent valve (8) is a ball valve, in which the ball (9) is pressed against a seat (10) by a pressure spring (11), while the pressurized oil acts on the ball in the opposite direction.

3. Nozzle unit according to claim 1, characterised in that the pressure dependent valve (8) comprises a valve seat (38) co-operating with a closing member in the shape of a diaphragm (37), where the pressurized oil forces the diaphragm (37) away from the valve seat, and a piston (39) biased by a resilient member (40), forces the diaphragm (37) towards the valve seat (38).

4. Nozzle unit according to claim 3, characterised in that when the pressure dependent valve (8) is in the closed state, the pressurized oil acts only on a partial area of the diaphragm (37) in the form of a ring shaped area extending around the valve seat (38), and when the pressure dependent valve (8) is in the open state the pressurized oil acts on a significantly larger area of the diaphragm (37), preferably the whole area of the diaphragm (37) facing towards the valve seat (38).

5. Nozzle unit according to claim 4, characterised in that the valve unit (50) comprises a cylinder shaped housing (35), comprising a circumferential channel (47), a ring shaped channel (41) facing the ring shaped area, a radial channel (42), connecting the circumferential channel (47) with the ring shaped channel (41) and a circumferential groove in which an o-ring (46) is placed, and a cup shaped cylinder (36), being fixed to the cylinder shaped housing. (35) and containing the piston (39) and the resilient member (40) in the form of a spring (40), where the diaphragm (37) is fixed between the cup shaped cylinder (36) and the cylinder shaped housing (35), and between the surface of the cylindrical space (27) and the cylinder shaped housing (35) there is a passage (45) that makes it possible for pressurized oil to reach the circumferential channel (47).

6. Nozzle unit according to claim 5, characterised in that the passage (45) is formed by at least one channel on one of the cylinder shaped housing (35) or the surface of the cylindrical space (27).

7. Nozzle unit according to claim 5, characterised in that the passage (45) is formed by having an external diameter of the cylinder shaped housing (35) permitting the passage of the pressurized oil to the circumferential channel (47).

8. Nozzle unit according to one of the claims 1 to 7, characterised in that sealing between nozzle (2) and nozzle holder (26) is formed by a sealing ring (23) fixed on the nozzle (2), where the sealing ring (23) seals against a ring shaped shoulder (25) in the nozzle holder (26).

9. Nozzle unit according to one of the claims 1 to 8, characterised in that the valve unit (50) is mounted in a nozzle holder (26) mounted in a normal oil preheater outlet.

Ansprüche

1. Düseneinheit (1) zum Zerstäuben von unter Druck gesetztem Öl in einem Ölbrenner, wobei die Düseneinheit (1) einen Düsenhalter (26) mit einem inneren zylinderförmigen Raum (27), eine Düse (2), die in dem Düsenhalter (26) befestigt ist, und ein druckabhängiges Ventil (8), das in einer Ventileinheit (50) aufgenommen ist, aufweist, dadurch gekennzeichnet, daß die Ventileinheit (50) in dem zylindrischen Raum (27) des Düsenhalters (26) angeordnet ist, so daß sie durch das unter Druck gesetzte Öl in Anlage gegen die Düse (2) oder einen Düsenfilter (5) auf der stromabwärts gerichteten Seite gepreßt wird, während keine Teile der Düseneinheit (1) gegen die Ventileinheit (50) auf der stromaufwärts gerichteten Seite anliegen.

2. Düseneinheit nach Anspruch 1, dadurch gekennzeichnet, daß das druckabhängige Ventil (8) ein Kugelventil ist, in dem die Kugel (9) durch eine Druckfeder (11) gegen einen Sitz (10) gedrückt wird, während das unter Druck gesetzte Öl auf die Kugel in die entgegengesetzte Richtung wirkt.

3. Düseneinheit nach Anspruch 1, dadurch gekennzeichnet, daß das druckabhängige Ventil (8) einen Ventilsitz (38) aufweist, der mit einem Schließelement in der Form einer Membran (37) zusammenwirkt, worin das unter Druck gesetzte Öl die Membran weg von dem Ventilsitz belastet und ein Kolben (39), der durch ein elastisches Element (40) vorgespannt ist, die Membran in Richtung auf den Ventilsitz (38) belastet.

4. Düseneinheit nach Anspruch 3, dadurch gekennzeichnet, daß, wenn das druckabhängige Ventil (8) im geschlossenen Zustand ist, das unter Druck gesetzte Öl lediglich auf einen Teilbereich der Membran in der Form eines ringförmigen Bereichs wirkt, der sich um den Ventilsitz (38) herum erstreckt, und, wenn das druckabhängige Ventil (8) im geöffneten Zustand ist, das unter Druck gesetzte Öl auf einen wesentlich größeren Bereich der Membran (37) wirkt, vorzugsweise den gesamten Bereich der Membran (37), der in Richtung auf den Ventilsitz (38) blickt.

5. Düseneinheit nach Anspruch 4, dadurch gekennzeichnet, daß die Ventileinheit (50) ein zylinderförmiges Gehäuse (35) aufweist, das einen Umfangskanal (47), einen ringförmigen Kanal (41), der dem ringförmigen Bereich gegenüberliegt, einen Radialkanal (42), der den Umfangskanal (47) mit dem ringförmigen Kanal (41) verbindet, und eine Umfangsnut, in der ein O-Ring (46) angeordnet ist, und einen becherförmigen Zylinder (36) aufweist, der an dem zylinderförmigen Gehäuse (35) befestigt ist und den Kolben (39) und das elastische Element (40) in der Form einer Feder (40) enthält, wobei die Membran (37) befestigt ist zwischen dem becherförmigen Zylinder (36) und dem zylinderförmigen Gehäuse (35), und es zwischen der Oberfläche des zylindrischen Raumes (27) und dem zylinderförmigen Gehäuse (35) einen Durchgang (45) gibt, der es für das unter Druck gesetzte Öl möglich macht, den Umfangskanal (47) zu erreichen.

6. Düseneinheit nach Anspruch 5, dadurch gekennzeichnet, daß der Durchgang (45) durch mindestens einen Kanal entweder auf dem zylinderförmigen Gehäuse (35) oder der Oberfläche des zylindrischen Raumes (27) gebildet ist.

7. Düseneinheit nach Anspruch 5, dadurch gekennzeichnet, daß der Durchgang (45) dadurch gebildet ist, daß man einen äußeren Durchmesser des zylinderförmigen Gehäuses (35) hat, der den Durchgang von unter Druck gesetztem Öl zu dem Ümfangskanal (47) erlaubt.

8. Düseneinheit nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, daß eine Dichtung zwischen Düse (2) und Düsenhalter (26) gebildet ist durch einen dichtenden Ring (23), der auf der Düse (2) befestigt ist, wo der dichtende Ring (23) gegen eine ringförmige Schulter (25) in dem Düsenhalter (26) dichtet.

9. Düseneinheit nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß die Ventileinheit (50) in einem Düsenhalter (26) montiert ist, der in einem normalen Ölvorwärmer-Ausgang montiert ist.

Revendications

1. Unité de buse (1) pour atomiser un mazout sous pression dans un brûleur à mazout, l'unité de buse (1) comprenant un porte-buse (26) ayant un espace intérieur cylindrique (27), une buse (2) fixée sur le porte-buse (26) et un clapet dépendant de la pression (8) logé dans une unité de clapet (50), caractérisée en ce que l'unité de clapet (50) est disposée dans l'espace cylindrique (27) du porte-buse (26) afin qu'elle soit comprimée par le mazout sous pression de façon à buter contre la buse (2) ou contre un filtre de buse (5) sur le côté aval, alors qu'aucune partie de l'unité de buse (1) ne bute contre l'unité de clapet (50) sur le côté amont.

2. Unité de buse selon la revendication 1, caractérisée en ce que le clapet dépendant de la pression (8) est un clapet à bille, dans lequel la bille (9) est pressée contre un siège (10) par un ressort de pression (11), alors que le mazout sous pression agit sur la bille dans la direction opposée.

3. Unité de buse selon la revendication 1, caractérisée en ce que le clapet dépendant de la pression (8) comprend un siège de clapet (38) coopérant avec un élément de fermeture ayant la forme d'une membrane (37), le mazout sous pression éloignant la membrane (37) du siège de clapet, et un piston (39) sollicité par un élément élastique (40), pousse la membrane (37) vers le siège de clapet (38).

4. Unité de buse selon la revendication 3, caractérisée en ce que, lorsque le clapet dépendant de la pression (8) est à l'état fermé, le mazout sous pression agit uniquement sur une surface partielle de la membrane (37) qui a la forme d'une surface annulaire s'étendant autour du siège de clapet (38) et, lorsque le clapet dépendant de la pression (8) est à l'état ouvert, le mazout sous pression agit sur une surface significativement plus grande de la membrane (37), de préférence sur toute la surface de la membrane (37) tournée vers le siège de clapet (38).

5. Unité de buse selon la revendication 4, caractérisée en ce que l'unité de clapet (50) comprend un boîtier cylindrique (35), comprenant un canal périphérique (47), un canal annulaire (41) faisant fasse à la surface annulaire, un canal radial (42) reliant le canal périphérique (47) au canal annulaire (41) et une rainure périphérique dans laquelle un joint torique (46) est placé, et un cylindre en forme de cuvette (36) fixé sur le boîtier cylindrique (35) et contenant le piston (39) et l'élément élastique (40) qui a la forme d'un ressort (40), dans laquelle la membrane (37) est fixée entre le cylindre en forme de cuvette (36) et le boîtier cylindrique (35), et entre la surface de l'espace cylindrique (27) et le boîtier cylindrique (35) se trouve un passage (45) qui permet au mazout sous pression d'atteindre le canal périphérique (47).

6. Unité de buse selon la revendication 5, caractérisée en ce que le passage (45) est formé par au moins un canal soit sur le boîtier cylindrique (35), soit sur la surface de l'espace cylindrique (27).

7. Unité de buse selon la revendication 5, caractérisée en ce que le passage (45) est formé par un diamètre extérieur du boîtier cylindrique (35) permettant le passage du mazout sous pression vers le canal périphérique (47).

8. Unité de buse selon l'une quelconque des revendications 1 à 7, caractérisée en ce que l'étanchéité entre la buse (2) et le porte-buse (26) est formée par une bague d'étanchéité (23) fixée sur la buse (2), dans laquelle la bague d'étanchéité (23) assure l'étanchéité par rapport à un épaulement annulaire (25) dans le porte-buse (26).

9. Unité de buse selon l'une quelconque des revendications 1 à 8, caractérisée en ce l'unité de clapet (50) est montée dans un porte-buse (26) installé dans une sortie de préchauffeur de mazout normal.

Drawing