FR2755752A1 - HYDRAULIC MODULE FOR CENTRAL HEATING AND HOT WATER PRODUCTION INSTALLATIONS, AND BOILERS EQUIPPED WITH SUCH A MODULE - Google Patents

Abstract

The boiler comprises a burner (3) topped by a combustion chamber (4) run through by a water heating conduit (8) and topped by an extractor (7). A hydraulic seat (14) supports a pump (47), a three-way valve (44), a domestic water flow rate sensor (92); and a heating water-domestic water exchanger (43). The exchanger (43) is arranged along the longitudinal direction of the seat (14). The pump (47) is set beyond one of the ends of the exchanger. The valve (44) and the sensor (53) are vertically oriented between these two. The fuel supplying components (17, 18) are separated from the seat (14). The invention is useful for reducing the cost of the seat and for standardising it for several types of boilers.

Description

DESCRIPTION
The present invention relates to a hydraulic module providing exchange, distribution and connection functions for a central heating installation and hot water production.

 The present invention also relates to a boiler equipped with such a module.

 EP-A-O 236 235 discloses an integrated boiler of the type targeted by the invention. One of the essential components of this boiler is a distribution, exchange and adjustment base on which almost all of the functional parts of the boiler are grafted. These are in particular the switching elements between the "central heating" mode and the "domestic hot water production" mode, components for regulating the fuel flow, the pump, various detectors, and a heat exchanger intended to heat domestic water from water, belonging to a separate circuit, passing through a combustion chamber of the boiler. The base has internal passages ensuring the various necessary connections between all these components as well as with the inlet and outlet orifices of the various fluids concerned.

 This base considerably simplifies the assembly and maintenance of the boiler when the latter is of a type well determined in advance, in particular as regards the nature of the fuel used. On the other hand, the base constitutes an expensive foundry piece because it is complex. Several models of this base may be necessary to make a range of boilers, depending for example on their power or the fuel used.

 The purpose of the present invention and to provide a hydraulic module which is less expensive and more flexible to use than the known base, provided with its associated components.

 The present invention also aims to provide a boiler incorporating such a module.

According to a first aspect of the invention, the hydraulic module for central heating and hot water production installation, comprising a base having:
- two boiler circuit orifices intended to receive between them, a hydraulic path passing through a combustion chamber,
- two orifices of the sanitary circuit, one constituting a sanitary cold water inlet orifice and the other a sanitary hot water outlet orifice,
a starting orifice and a heating circuit return orifice, intended to functionally receive between them a heating circuit comprising at least one heating appliance such as a radiator,
the supporting base: a circulation pump, a three-way valve selectively defining a first and a second flow path, and a heat exchanger having a heat emitting path and a heat receiving path functionally mounted between the two orifices of the sanitary circuit, the two heating circuit orifices being connected to internal passages in the base so that in service the heating circuit is mounted in series with the pump and the first path of the three-way valve between the two boiler circuit ports, and the heat emitting path of the heat exchanger being mounted in series with the pump and said second flow path of the three-way valve between the two boiler circuit ports, is characterized in that the heat exchanger has an elongation direction parallel to that of the base and the circulation pump is placed on the base beyond one of the ends the length of the heat exchanger.

 Thus, according to the invention, there is provided a base of markedly reduced format, for example typically two times smaller on the surface, and also less thick, than the known base. According to the invention, the components which are associated with the base are selected to form the module and those which it is acceptable to place outside the module. In particular, according to a preferred feature of the invention, the base is completely free of conduits or other means containing fuel. Thus, the module operates independently of the fuel used by the boiler, whether it is a specific quality of gas or whether it is fuel oil.

 According to a feature having its own interest, the module does not have any dynamic type sealing involved in the operation of the module's automatic systems. By "dynamic sealing" is meant, conventionally, a sealing in which there is relative sliding movement between a sealing surface and a sealing member resting on it. In particular, the three-way valve preferably comprises a movable shutter between two opposite seats each cooperating with one of the faces of the shutter, which is mounted at one end of an oscillating lever whose other end is connected to control means, while a geometric axis of oscillation of the lever is located between the two ends, substantially in the plane of a membrane in which the lever is tightly fitted. When the lever oscillates to establish one of the paths and interrupt the other path of the three-way valve, the membrane deforms without there being any relative movement between the lever and the region of the membrane which is in contact with the lever.

 In known installations, in "central heating" operation, the water flow rate can decrease very sharply if all the radiators are closed or almost closed simultaneously. This can happen by chance if the radiators are fitted with thermostats.

Such a reduction in flow is detrimental to the proper functioning of the boiler and the automatic systems associated with it.

 According to another particular feature of specific interest, means, such as return means, apply to the shutter of the three-way valve a limited force keeping the shutter in the position closing the second flow path of the valve to three-way, which is mounted between the return port of the heating circuit and the start port of the boiler circuit. Beyond a predetermined pressure difference between the heat emitting path of the exchanger and the return orifice of the heating circuit, the shutter moves under the effect of the pressure difference, against of the aforementioned limited force and an additional flow becomes possible through the emitting path of the heat exchanger.

 So when the module feeds the central heating circuit, the domestic water heating path is activated even in the absence of domestic hot water withdrawal when the pressure rises excessively, and the flow decreases excessively, due to '' a total or almost total closure of all or almost all heating radiators. This improves the overall operation of the installation.

 Known installations have an additional disadvantage in summer. After a domestic hot water withdrawal by a user, the three-way valve automatically returns to its rest position corresponding to the switching on of the central heating. But the combustion chamber does not cool immediately, and it then starts to feed a thermosyphon which causes an undesired rise in temperature in certain radiators placed in the high position in the central heating installation.

 According to a feature which also has its specific interest, the invention remedies this defect by proposing means to delay the re-establishment of the first path - or "central heating" path - of the three-way valve after the water flow has disappeared when the installation has been placed, for example by means of a switch, in a "summer" position. The delay may be of a predetermined duration.

Another possibility is to delay the re-establishment of the "central heating" path of the three-way valve until the temperature at the outlet of the combustion chamber drops below a predetermined value.

 According to its second aspect, the invention also relates to a boiler equipped with a module according to the first aspect, and comprising a combustion chamber traversed by a hydraulic path connected by each of these ends to one of the orifices of the boiler circuit, and fuel supply means connected to a burner heating the hydraulic path in the combustion chamber.

 Other features and advantages of the invention will emerge from the description below, relating to a non-limiting example.

In the accompanying drawings:
- Figure 1 is a schematic front view of a gas boiler according to the invention;
- Figure 2 is a schematic profile view of the boiler of Figure 1;
- Figure 3 is a schematic view of a heating and domestic hot water production circuit implementing the module according to the invention, for example in a boiler according to Figures 1 and 2;
- Figure 4 is a front view of the module according to the invention;
- Figures 5 to 7 are sections along VV, VI
VI and respectively VII-VII of Figure 4;
- Figure 8 is a front view of the base; and
- Figure 9 is a view of the base in section in a plane substantially parallel to its front and rear faces.

 In the example represented in FIGS. 1 and 2, the boiler, of wall type, comprises a vertical frame 1 in the form of a box supporting a parallelepipedic housing 2, the whole being only briefly shown. The frame 1 supports a burner 3 surmounted by a combustion chamber 4 including a combustion gas / water exchanger 6 surmounted by a combustion gas extractor 7. The "water" path 8 (FIG. 1) of the exchanger 7 is mounted between two water conduits 9 and 11 which are connected to two respective boiler circuit orifices 12 and 13 placed at the two opposite ends of the upper edge of a base 14 belonging to a hydraulic module 16 grouping together the distribution exchange functions and hydraulic connection. The base 14 has a generally rectangular rectangular shape and it is arranged in a vertical plane at the base of the boiler in front of the vertical frame 1. The boiler circuit 8, 9, 11 is also connected to an expansion tank 10 (figure 2) located at the top of box 1.

 The boiler also comprises, separately from the module 16 and in particular from the base 14, gas supply means for the burner 3, which in particular comprise a supply duct 17 and a device 18 called a "gas valve" ", all located in the vertical frame.

 As shown in Figure 3, the base 14 has on its rear face an alignment of four connection holes of the boiler and in particular of the module 16 with the central heating installation and sanitary water distribution. The two extreme orifices are an orifice 19 for the return of the central heating circuit 21 and respectively an orifice 22 for the start of this same circuit 21. The orifice 19 is near the same end of the base as the orifice 12 for departure of the boiler circuit 8, 9, 11, and the orifice 22 is close to the same end of the base 14 as the orifice 13 of return of the boiler circuit 8, 9, 11.

 The circuit 21 includes heating radiators 23 hydraulically mounted in parallel between the orifices 19 and 22.

 Between the openings 19 and 22 are disposed a domestic cold water inlet orifice 24, close to the return orifice 19 of the heating circuit, and a domestic hot water start orifice 26 close to the orifice 22 of the heating circuit.

 The sanitary cold water inlet orifice 24 is connected to a cold water inlet illustrated by a water meter 27, and to the cold water installation illustrated by a cold water tap 28. L the domestic hot water outlet 26 is connected to the domestic hot water distribution installation illustrated by a hot water tap 29.

 Stop valves 31, each associated with one of the orifices 19, 22, 24, 26, are mounted along the lower edge 34 of the base 14. A stop valve 31 is illustrated for example in FIG. 6 in connection with the orifice 19. The body of the valve is defined by the wall of a cavity 32 formed in the base 14. A valve mechanism 33 is fixed in a hole making the cavity 32 communicate with the outside at through the lower edge 34 of the base 14. The mechanism 33 carries a rotary control rod 36 whose one end inside the cavity 32 carries a movable shutter 37 cooperating with a seat 38 through which the cavity 32 communicates with an internal passage 39 of the base 14.

 As shown in particular in FIGS. 5 to 9, the base 14 defines different internal passages, such as the passage 39 which has just been described, and cavities such as the cavity 32 also described above. We will first write with reference to Figure 3 the diagram that these passages and cavities make between the orifices 12, 13, 19, 22, 24, 26, of the base 14. An internal passage 41 communicates the opening 13 of the boiler circuit with the opening 22 of the heating circuit, passing through a connection point 42 with one of the inputs of a heat exchanger 43 which is illustrated by two crossed arrows in the figure 3. The orifice 19 of the heating circuit return communicates with the orifice 12 of the boiler circuit via a first path 46-56 of a three-way valve 44 and, between the common access 46 of this and the orifice 12, of a pump - or circulator -47. Thus, when the three-way valve 44 is in the position shown in FIG. 3, heating water operates in a closed circuit, thanks to the pump 47 between the exchanger 8, the conduit 11, the orifice 13, the passage 41, the orifice 22, the radiators 23, the heating return orifice 19, the first path 46-56 of the three-way valve 44, the pump 47, the starting point of the boiler circuit 12 and the conduit 9.

 The opening 26 of the domestic hot water circuit is connected by an internal passage 48 of the base with an exit point 49 of the exchanger 43 located at the downstream end of a heat receiving path 51 of the exchanger 43, the entry point 52 of which is connected to the entry orifice 24 by means of a flow detector 53. The flow detector supplies an electrical signal via a line 54 which is used to control the valve three-way 44 for, in the event of a flow in the domestic hot water circuit, pass the valve 44 from the rest position which has been described previously to a position where the first path - or path "central heating of this valve , between accesses 46 and 56, is interrupted while a second path - or path "domestic hot water production" - of the valve, between common access 46 and a second selective access 57, is established so as to connect the common access 46 and therefore the inlet of the pump 47 with the downstream end 58 of the heat emitting path 59 of the exchanger 43. Thus, when the three-way valve deactivates path 46-56 and activates path 46-57, the heating water circulates in a closed circuit by the exchanger 8, the duct 11, the orifice 13 for the return of the boiler circuit, the passage 41, the heat emitting path 59 of the exchanger 43, the path "production of sanitary hot water" 57-46 of the three-way valve 44, the pump 47, the opening 12 of the boiler circuit and the conduit 9. The water no longer circulates through the central heating circuit 21 because the three-way valve 44 interrupts this circuit.

 The signal supplied by the flow detector 53 is transmitted to the three-way valve 44 via a summer-winter switch 61. In the winter position shown, the switch 61 directly transmits the signal from the detector 53 to the valve 44, so that as soon as the flow in the domestic hot water circuit disappears, the three-way valve 44 returns to the rest position shown in FIG. 3.

 Thus, central heating is restored as soon as the drawing of domestic hot water stops.

 When the switch 61 is in the summer position, the signal from the domestic hot water flow detector 53 is modified by a stage 62 which is connected to a temperature probe 63 exposed to the heating water arriving through the orifice 13. The stage 62 has the function of extending the signal sent to the three-way valve 44 after the disappearance of the domestic hot water flow as long as the temperature at the outlet of the combustion chamber 8 remains above a certain threshold, for example example 30 "C. Thus, as long as the water is hot, the domestic water heating circuit remains established and the central heating circuit interrupted. This avoids the undesirable effect of thermosiphon in the direction of the radiators 23 after each drawing hot water in summer This thermosyphon effect results from the fact that in practice at least some of the radiators 23 are placed much higher than the combustion chamber 4, for example on a higher floor of a building.

 The signal provided by the temperature probe 63 also serves to control the gas valve 18, in a known manner which in itself is not part of the invention.

 We will now describe in more detail the specific features of the module.

 In general, the distribution components are entirely housed in the base while the electrical and / or thermal function components are fixed on the front face of the base, therefore on the face opposite to the orifices 19, 22, 24, 26.

The pump 47 (FIGS. 4 and 5) is thus fixed in a sealed manner on an appropriate surface of the base.

The suction space 66 of the pump communicates with a cavity 67 of the base 14 (Figures 5 and 9) leading to the common access 46 of the three-way valve. The discharge space 68 of the pump 47 communicates with a cavity 69 of the base 14 connected to the orifice 12 at the start of the boiler circuit.

 The heat exchanger 43 is a plate exchanger suitably fixed on the front face of the base 14. FIG. 8 shows that the four connections 42, 49, 52, 58 of the exchanger 43 are made in the form of orifices suitably positioned through the front face of the base. These orifices communicate in leaktight manner with corresponding orifices (not shown) provided on the bearing face of the heat exchanger 43.

 The internal passages arranged in the base realize the interconnections which have been described previously and which are visible in their practical realization possible in FIGS. 8 and 9. FIG. 8 also illustrates, through the front face of the base, the hole of mounting 71 for the temperature probe 63 as well as a mounting hole 72, also opening into the passage 41, for the safety valve of the heating circuit 73 (FIGS. 4 and 5).

 We will now describe in more detail, with reference to FIG. 6, the three-way valve 44.

This comprises a shutter 74 which is movable in a cavity 76 of the base 14 between two opposite seats which constitute one the selective access 56 and the other the selective access 57. The shutter 74 is mounted at the end of an oscillating lever 77, the other end 78 of which is subjected to the action of an actuator 79 comprising a return spring 81 tending permanently to return the lever 77 to the position in which the shutter 74 closes the second access 57 and opens the first access 56 to carry out the "central heating" operating mode. The actuator 79 also includes an electromagnet 82 which, when excited by the signal produced by the domestic water flow detector 53, causes the lever 77 to tilt, against the action of the return spring 81, in the position in which the first access 56 is closed and the second access 57 is open, to carry out the "domestic hot water drawing" operation.

 By examining FIG. 3, it will be understood that in "central heating" operation, the pressure rises upstream of the radiators 23 when, by coincidence of their respective regulation, they are all closed or almost closed at the same time. This overpressure is transmitted to the second access 57 via the heat emitter path 59 of the exchanger. Returning to FIG. 6, to avoid the drawbacks linked to this overpressure and to the low flow velocities which accompany it, in particular in the water path 8 of the exchanger 7 of the combustion chamber, the spring 81 is produced under the form of a calibrated spring which authorizes the detachment of the shutter 74 relative to the seat constituting the second port 57 when the pressure in the second port 57 exceeds a certain threshold. In this situation, a certain flow rate is established through the path 59 of the exchanger and the second access from the three-way valve, which increases the overall flow rate of the pump 47, eliminates its possible operating noise and / or its cavitation, improves the operation of the combustion gas / water exchanger 6 as well as the regulation in particular by means of the temperature probe 63.

 Returning to FIG. 6, the actuator 79, as an electrical function component, is fixed to the front face of the base 14, externally to the latter.

The lever 77 passes from the interior of the actuator 77 to the interior of the cavity 76 through a sealing membrane 83 which seals the cavity 76 by being pinched around its entire periphery between two corresponding surfaces of the base 14 and of the actuator housing 79. The membrane 83 comprises a part 84 in the form of a thermowell which completely sheaths the lever 77 on the side of the cavity 76. The part 84 forms at its end the shutter 74 comprising two opposite faces 86 intended to cooperate each in a sealed manner with a respective one of the seats 56 and 57. Thus, any dynamic sealing, that is to say by sliding sealing surfaces against one another, is absent from the three-way valve which has just been described. The lever 74 oscillates around a geometric axis substantially located at 87, perpendicular to the plane of Figure 6, and in the plane of the membrane 83. The two faces 86 of the shutter 74 form a slight angle with respect to to the other so that each is able to rest flat on its respective seat despite the angle of oscillation of the lever 77 between its two extreme positions.

 We will now describe with reference to Figure 7 the device 53 for detecting the flow of domestic hot water.

 This device comprises a mobile 88 of triangular section (in a horizontal plane perpendicular to the plane of FIG. 7) mounted to slide in a vertical cavity 89 of the base 14. The mobile 88 carries at its upper end a magnetic zone 91 capable of influence a Hall sensor 92 mounted in leaktight fashion through the front face of the base 14.

In the absence of flow, the mobile 88 falls into the position shown in FIG. 7 by pressing on a stopper 90 permeable to the flow coming from the orifice 24 for the arrival of sanitary cold water. In the event of a flow, the hydraulic friction drives the mobile 88 upwards, which influences the
Hall 92 which in turn delivers the signal controlling the permutation of the three-way valve 44. Again, a system has been found to perform the desired function without resorting to dynamic sealing between the water circuits and the outside .

 A degasser 96 is tightly fixed in an orifice 97 provided for this purpose at the top of the base in communication with the cavity 67.

 The only dynamic seals of the modules are those necessary for the shut-off valves 31 but these are only very rarely operated during the life of the device, and the inevitable dynamic sealing around the pump shaft 47 .

 As shown in FIG. 4, the heat exchanger 43 has a generally quasi-rectangular shape with a direction of horizontal elongation and parallel to the direction of elongation of the base 14. The pump 47 is arranged beyond one of the ends of the length of the exchanger 43. The width of the exchanger 43 and the diameter of the pump 47 correspond approximately to the width (vertical) of the base 14. Between the exchanger 43 and the pump 47, the domestic hot water flow detector 53 and the three-way valve 44 are arranged one next to the other in a generally vertical orientation, that is to say parallel to the width base 14 and exchanger 43.

 At the other end of the exchanger 43, the temperature probe 63 and the safety valve 73 are arranged one above the other.

 Thus, the dimensions of the base 14, and consequently its cost of production, are considerably reduced compared to the production according to EP-A-0 236 235. The base 14 according to the invention can for example have a length less than 500 mm and a width less than a quarter of its length.

 In the example shown, the base 14 is made in the form of a bronze or brass foundry piece or even a piece of injected plastic. Such a plastic material can be glass-filled polyamide 6-6, molded according to the technique known as fusible cores, according to which the molding cores are removed by fusion in hot water.

 Unlike the base described in EP-A-O 236 235, the internal cavities of the base 14 according to the invention do not need to overlap anywhere. The base is thus achievable by welding one against the other two sheets each suitably shaped, the welds being made along the contact lines corresponding on the one hand to the periphery of the base and on the other hand along the separation lines of the different cavities. Connections to the outside are, if necessary, made by welding added parts, serving for example as a support plate for the added components, or inlet and outlet orifices.

 In the example described and shown in FIGS. 1 and 2, the base is integrated in a boiler, but the module according to the invention can also be produced in the form of a separate module located at a distance from the boiler.

Claims (19)

 (14) and the circulation pump (47) is placed on the base (14) beyond one of the ends of the length of the heat exchanger (43).  the supporting base: a circulation pump (47), a three-way valve (44) selectively defining a first and a second flow path, and a heat exchanger (43) having a heat emitting path (59) and a heat receiving path (51) operatively mounted between the two sanitary circuit orifices (24, 26), the two heating circuit orifices (19, 22) being connected to internal passages (41) in the base (14 ) so that in service the heating circuit (21) is mounted in series with the pump (47) and the first path (46-56) of the three-way valve between the two boiler circuit orifices (12, 13 ), and the heat emitting path (59) of the heat exchanger being mounted in series with the pump (47) and said second flow path (46-57) of the three-way valve between the two orifices ( 12, 13) of the boiler circuit, characterized in that the heat exchanger (43) has a parallel direction of elongation to the that of the base  (21) comprising at least one heating device (23) such as a radiator,  (19) heating circuit, intended to functionally receive a heating circuit therebetween  - a start port (22) and a return port  - two sanitary circuit orifices (24, 26), one constituting a sanitary cold water inlet orifice (24) and the other a sanitary hot water outlet orifice (26),  - two boiler circuit orifices (12, 13) intended to receive between them a hydraulic path (8, 9, 11) passing through a combustion chamber (4),  Hydraulic module for central heating and hot water production installation, comprising a base (14) having:  2. Module according to claim 1, characterized in that the pump (47) and the heat exchanger (43) have substantially the same size according to the width of the base (14).  3. Module according to claim 1 or 2, characterized in that the three-way valve (44) is arranged on the base (14) between the pump (47) and the heat exchanger (43).  4. Module according to one of claims 1 to 3, characterized in that the three-way valve (44) comprises a shutter (74) mounted movably between two opposite seats (56, 57) each cooperating with one of the faces (86) of the shutter, which is mounted at one end of an oscillating lever (77), the other end (78) of which is connected to control means  (79), and in that a geometric axis (87) of oscillation of the lever is located between the two ends (74, 78) of the lever, substantially in the plane of a membrane  (83) in which the lever is tightly fitted.  5. Module according to one of claims 1 to 4, characterized by means applying to the shutter  (74) of the three-way valve (44) a limited force keeping the shutter in position interrupting the second flow path (57) of the three-way valve, which is mounted between the return orifice (19) of the heating circuit and the flow opening  (12) of the boiler circuit so that beyond a predetermined pressure difference between the heat emitting path (59) and the orifice (19) of the heating circuit return, the shutter (74) is moved against the limited force to restore the second flow path (57) of the three-way valve.  6. Module according to one of claims 1 to 5, characterized in that it comprises means (53) for detecting the flow of water in the sanitary path and for controlling the interruption of the first flow path (56 ) and the establishment of the second flow path (57) when such a water flow is detected, and means (62, 63) for introducing a delay in the restoration of the first path and in the interruption of the second path after the disappearance of said water flow.  7. Module according to claim 6, characterized in that said delay lasts until, in a summer position, the temperature at the outlet of the boiler circuit drops below a predetermined value.  8. Module according to one of claims 1 to 7, characterized in that it comprises as means for detecting the flow of water in the sanitary path a mobile (88) placed in the sanitary path and tending to be driven by the water flow to a mobile presence sensor (92).  9. Module according to claim 8, characterized in that the mobile (88) is mounted in a cavity (89) of the base (14).  10. Module according to one of claims 1 to 9, characterized in that among the components and conduits associated with the base (14), the conduits and the distribution components are housed in the base  (14) and the components (43, 44, 47, 92, 63, 73) of electrical and / or thermal function are fixed on the same face of the base (14).  11. Module according to one of claims 1 to 10, characterized in that the length of the base (14) is at most of the order of 500 mm.  12. Module according to one of claims 1 to 11, characterized in that cut-off valves (31) are associated with at least some (19, 22, 24, 26) of said orifices.  13. Module according to claim 12, characterized in that the orifices (19, 22, 24, 26) associated with taps (31) are substantially aligned on a rear face of the base (14), and the taps (31 ) are aligned along a lower edge (34) of the base (14) -  14. Module according to one of claims 1 to 13, characterized in that the base (14) is free of any fuel circuit and of any component intended to contain fuel.  15. Module according to one of claims 1 to 14, characterized in that the base (14) is a foundry piece.  16. Module according to one of claims 1 to 14, characterized in that the base (14) is a plastic injection part.  17. Module according to one of claims 1 to 14, characterized in that the base comprises two sheets suitably shaped by stamping and probed together along lines delimiting the various internal passages to be produced, metal parts being welded to said sheets to form connecting surfaces with the outside.  18. Boiler equipped with a module according to one of claims 1 to 17, characterized in that it comprises a combustion chamber (4) traversed by a hydraulic path (8) connected by each of its ends to one orifices (12, 13) of the boiler circuit, and means (17, 18) of fuel supply connected to a burner (3) heating the hydraulic path (8) in the combustion chamber (4).  19. Boiler equipped with a module according to one of claims 1 to 17, characterized in that the fuel supply means (17, 18) are separated from the base (14).