The present invention relates to a dosing device for the continuous dosing of powder.

Various systems for the continuous dosing of powder are known.

In the pharmaceutical industry, mostly "loss in weight" dosing- systems (LIW) are applied due to their accuracy.

Said "loss in weight" devices consist of a tank that is filled with powder via an entry and can be emptied in a controlled manner by means of Archimedes screws or vibrations or sliding movements or valves or the like at the exit.

The assembly is placed on scales with which the drop in weighed weight over time is a reflection of the mass flow of the powder .

However, said LIW dosing devices have various disadvantages.

They are sensitive to vibrations from the surroundings and must consequently be set. up in a vibration-free manner for a precise measurement result.

When filling the tank, the drop in weight cannot be measured such that the Archimedes screws must temporarily run without measurement .

Filling the tank must consequently be done quickly and may cause significant ripples in the mass flow.

The entry and the exit of the tank of a LIW device must be coupled to the fixed world with flexible bellows to ensure a dust-free powder transport and at the same time limit exterior influence on the measuring and regulating system as much as possible .

The assembly of said bellows is critical for the efficient operation of the measurement system.

Said,bellows are also sensitive to accumulation of powder which can come loose in an uncontrolled,manner and interfere with the measurement.

All these irregularities may bbee problematic such that additional levelling may be desirable.

In addition, a relatively large amount of powder is lost, for example from the time of start-up until the operating state .is achieved, and powder which, oonn termination of the process remains in the many horizontal parts, corners and sides of the device .

For cleaning the dosing device, it. needs to be disassembled such that the loose components can be cleaned separately such that the dosing device is rather unsuitable for "cleaning in place (CIP)" or "wash in place (WIP)".

Disassembling and reassembling the dosing devices for cleaning and converting to other powders costs time, is labour-intensive and consequently is coupled with relatively high costs.

"Loss in weight" devices consequently give little flexibility to dosing processes and can be problematic when toxic powders are used. The purpose of the present invention is to provide a solution to one or more of the aforementioned and other disadvantages.

To this end, the invention relates to a dosing device for dosing the mass flow of powders, whereby it is a continuous flow device that contains a housing with an entry at the top for the powder to be dosed and an exit at the bottom for the dosed powder, whereby the entry ends centrally in the housing and contains a dosing valve with a regulatable outflow for the powder which is regulatable using a regulating system and whereby the housing contains a distribution wheel tthhaatt is coaxially mounted in the housing rotatably around a shaft around the dosing valve and is provided with an inlet,opposite the outflow of the dosing valve and an outlet at the outer contour of the distribution,wheel, whereby the dosing device is provided with a drive for driving the distribution wheel,at a set speed of rotation, and whereby the housing further contains a turbine wheel that is mounted rotatably coaxially around the distribution wheel for collecting the powder from the distribution wheel with an inlet opposite the outlet of the distribution wheel and an outlet, whereby there are means to determine at least one operating parameter of the turbine wheel, and whereby the aforementioned regulating system is provided to keep said operating parameter constant during use by regulating the outflow of the dosing valve.

Such dosing device is easy to realise and gives a continuous and constant powder flow at the exit.

The invention is based on the following principle. The turbine wheel is driven by the air flow coining from the distribution wheel, mixed with powder coming from the dosing valve according to the formula whereby F is the force which drives the turbine wheel, Q is the mass flow and v is the peripheral velocity of the distribution wheel.

According to the aforementioned formula the mass flow Q of the powder-air mixture is proportional to the driving force F of the turbine wheel provided that the peripheral velocity v of the distribution wheel is constant.

Consequently, there are different possibilities to generate a measurement signal by means of the turbine wheel that is proportional to the mass flow and to subsequently use said measurement signal to regulate the dosing valve.

A first possibility is to measure the force or the torque with which the turbine wheel can be locked.

A second possibility is to stop the turbine wheel by means of a weak spring which, allows aann angular rotation that is proportional to the mass flow.

A third possibility is to let the turbine wheel rotate freely whereby the speed of rotation increases until a balance is achieved between the driving force F and the frictional force of the turbine wheel such that, the speed of rotation of the turbine wheel becomes constant and is a measure for the mass flow.

The advantage of letting the turbine wheel rotate freely is that the set up and regulation is relatively simple and cheap and moreover that the impact of the powder against the turbine is minimal which is favourable for impact-sensitive powders.

Preferably, the turbine wheel is formed such that it can receive the kinetic energy of the powder coming from the distribution wheel maximally and convert said energy into a static or a dynamic torque or a speed of rotation without the turbine wheel being'hindered by the passing powder.

Preferably, the turbine wheel has a low mass inertia and is provided with a bearing or a. suspension that has a constant, preferably low friction to be able to optimally convert the changes in the mass flow into changes of the measurement signal of the turbine wheel.

The dosing device according to the embodiment offers the following advantages compared to the known LIW systems.

The mass flow of the dosed powder becomes very precise and unlike loss in weight" and "gain in weight" systems is kept under control uninterruptedly by controlling the torque or the angular rotation or the speed of rotation of the turbine wheel such that,the risk of irregularities that need to be levelled, is structurally less than with loss in weight,dosing devices.

Due to the absence of scales which continuously measure the weight of the present powder, the device needs no flexible connections or bellows such that it is soundly hermetically sealable such that it ccaann be used for dosing highly toxic substances. Another characteristic of said dosing device is that through the operation of the distribution wheel, the present horizontal parts where powder accumulation could occur are self-cleaning.

Further, the powder does not come into contact with horizontal surfaces such that after use very little powder remains in the device such that the device is simple to clean and is suitable for "CIP" and/or "WIP" cleaning.

The measuring and regulating system is relatively insensitive for interference from the surroundings such that no special provisions are necessary for mounting.

In a basic embodiment the dosing device can be adjusted,with external scales to define the desired measurement signal and has no monitoring for the stability of the frictional resistance of the turbine wheel.

Another characteristic of the operation of. the distribution wheel,is that the powder flow is homogenously distributed along the contour of the housing regardless of the turbine wheel which allows said powder flow to be adjustably divided in this location in at least two powder flows which at any moment have the same ratio relative to each other and of which one powder flow is the desired dosing flow and the other a residual flow of the excess powder.

An advantage of said division in said location is that the dosing valve can always function in an optimal operating area, also when the desired mass flow to the exit is significantly less such that very small precise dosings become possible. The distribution valve connects to a funnel with a separate exit for each of both flows.

Another advantage is that the residual flow during dosing can be used to check the progress of the mass flow of the dosing flow.

To this end. a monitoring system is provided in the dosing device to which the residual flow can be diverted for indirect monitoring for possible deviations of the delivered mass flow relative to the desired mass flow.

The monitoring system is provided to generate an error signal that can be used to issue an alarm signal or to feed back to the regulating system for adjustment of the governed speed of rotation of the turbine wheel.

Preferably, the monitoring system is executed with built-in "gain in weight" scales with an open collection jar that rests reversibly on a load cell which during filling with powder generates a gain in weight curve every time.

When the jar is full, it is turned around and the measured, powder can be discharged to a. collector to which a return system may be connected.

Thanks to a system of diverter valves, the dosing flow and the residual flow can be either directly diverted separately or jointly to the dosing exit or to the residual exit with the "gain in weight" scales or directly to a collector from where the collected powder is led back to the entry via a return system. The combination of diverter valves and built-in gain in weight scales offers the advantage that the dosing device can automatically adjust itself by, after entering the desired. mass flow, first defining the associated measurement signal of the turbine wheel and subsequently switching the correct mass flow to the exit.

The return system is for example executed with an Archimedes screw in a vertical tube for the vertical transport, of the residual powder from the aforementioned collector at the bottom to the entry of the dosing device at the top.

The advantage of supplying new powder via the collector is that the return system is the only system that is responsible for the powder level at the top at the entry of the device.

Preferably, said return system can be executed as a tube with an Archimedes screw.

The advantage of a tube with an Archimedes screw is that it is a very compact system and is easy to clean.

A central axial mounting of the device allows the Archimedes screw to be used directly as a dosing valve whereby the end of the screw directly disperses the upwardly transported,powder in or over the distribution wheel.

The advantage of axial mounting is that consequently a separate dosing valve and the monitoring of the powder level at the entry at the top can be omitted such that the embodiment is compact. With the intention of better showing the characteristics of the invention, a few preferred embodiments of a dosing device according to the invention are described hereinafter by way of an example, without any limiting nature, with,reference to the accompanying drawings, wherein:

Figure 1 A shows a 3D view of the basic embodiment of the dosing device according to the invention;

Figure 1B shows the basic embodiment of figure 1A without lid and supply pipe;

Figure 2 shows a central vertical cross-section of this basic embodiment;

Figure 3 shows an exploded view of the turbine part of figure 2;

Figure 4 shows an embodiment with locked turbine wheel;

Figure 5 shows an embodiment whereby the turbine wheel is stopped with a weak spring;

Figure 6 shows the preferred embodiment with freely rotating turbine wheel;

Figure 7 and 8 show a disassembled combination of dosing wheel, distribution wheel and turbine wheel;

Figure 9 shows possible embodiments of the distribution wheel ;

Figure 10 shows possible embodiments of the turbine wheel;

Figure 11 shows an embodiment of the distribution valve;

Figure 12 shows the double funnel;

Figures 13 and 14 show the distribution valve on the double funnel in two different ratio positions;

Figure 15 schematically shows the operation of the distribution valve on the double funnel;

Figure 16 shows the basic embodiment of the dosing device of figure 1 expanded with a diverter valves system., built- in gain in weight scales and.a return system for unused powder, new powder entry;

Figure 17 shows the switching of the diverter valves of figure 16 when all the dosed powder is guided to the exit; Figure 18 shows the switching of tthhee diverter valves during the start-up procedure;

Figure 19 shows the switching of diverter valves during operation,whereby the parallel flow is guided to the gain in weight scales;

Figure 20 shows an embodiment of the built-in gain in weight scales of the dosing device of figure 16;

Figure 21 shows aa central vertical cross-section, of a dosing device according to the invention with a central Archimedes screw as transport and dosing means;

Figure 22 shows a disassembled embodiment of the dosing device of figure 21.

The basic embodiment of a dosing device 1 according to the invention shown in figure 1 is intended for dosing the mass flow of powders, in particular for obtaining a desired set mass flow.

Said dosing device 1 is a continuous flow device, with a housing 2 composed of aa dome -shaped lid 2 at the top that connects to a funnel 49 that is vertically cylindrical at the top and ends at the bottom in an exit 5 for the dosed powder.

The lid 2 is provided with an entry 4 connecting to a supply pipe 60 for the supply of the powder to be dosed which is preferably centrally mounted. The entry 4 iiss also provided with a dosing valve 6 with regulatable outflow of the powder.

In this case the dosing valve 6 is executed. as a rotatable disk that is coaxially mounted in the entry 4 with a central upward facing cone and ribs 7 that they are arranged around, the base in a fan-like manner as shown in figures 2 to 8.

The dosing valve 6 can be provided with a drive 8 for dosing the mass flow of powder that is allowed to pass , in this case by adjusting the speed of rotation of the dosing valve 6. Said drive 8 is provided with a regulating system.19 with which the outflow of the dosing valve can be regulated.

In the dome-shaped lid, a distribution, wheel 9 is coaxially mounted 2 that is rotatable around the dosing valve 6 as shown in figures 2 to 8.

The distribution wheel 9 is provided here with blades 10 which delimit channels 11 with an inlet 12 opposite the outflow of the dosing valve 6 for receiving powder and an outlet 13 at the outer contour of the distribution wheel 9 along which the powder leaves the distribution wheel.

Preferably, the dosing device 1 is provided with a drive 50 shown in figure 2 and which gives the distribution wheel 9 a set constant speed of rotation 59. In the example of the figures the drive 50 is internally mounted in the housing.

Figure 9 shows embodiments of the distribution wheel 9 with open channels 11 and closed channels 11. In the extreme, an ordinary flat disk without blades can also be used to spread the powder.

Further, a turbine wheel 14 is coaxially mounted in the dome- shaped lid 2 which is freely rotatable around the distribution wheel 9 by means of a turbine bearing 48 as shown in figure 3.

Various embodiments of the turbine wheel 14 and associated adapted bearings 48 are possible as illustrated in figures 10

A to 10D.

Preferably, the turbine bearing 48 of the turbine wheel 14 has a small diameter and can be mounted centrally around, for example, the entry 4 at the top for turbine wheels according to figures 10 B and 10 D or at the bottom for turbine wheels according to figure 10 A and figure 1B.

In the example shown, the turbine wheel 14 is provided with blades 15 with an inlet 16 opposite the outlet 13 of a distribution wheel 9 and. an outlet 17 such that the powder from the distribution wheel 9 collides with the blades 15 of the turbine wheel 14 and is moved in the direction of the outlet 17 of the turbine wheel 14.

In the example shown in figures 7 and 8 the outlet 17 of the turbine wheel 14 faces downward. Examples of such turbine wheels 14 with a downward outlet 17 are shown in figures 10C and 10D.

In the embodiment according to figures 1 to 3 the outlet 17 of the turbine wheel is lateral facing, whereby the powder that leaves the outlet 17 of the turbine wheel 14 collides with the lid 2 and. subsequently goes down the funnel 49 such as, for example, with a turbine wheel 14 of the figures 10A and 10B.

In certain cases, a turbine wheel 14 without blades can also be used, in other words a turbine wheel 14 in the form of a flat ring or disk (not shown in the figures). Such turbine wheel 14 without blades can, for example, be advantageous in case of relatively sticky powders.

At the time that the distribution wheel 9 rotates. a radial air flow is produced in the distribution wheel 9 from the inlet

12 through the channels 11 to the outlet 13 which carries the powder, leaving the outlet of the dosing valve 6, from the moment that the dosing valve 6 starts to rotate and thus releases powder.

As a result of the constant speed of rotation 59 of the distribution wheel 9 on leaving the distribution wheel 9 said powder-air mixture has a clearly defined tangential speed 53 as shown in figures 4 to 6 with which the powder is flung against or over the turbine wheel 14.

The impact on the blades 15 and/or the friction causes a drive torque on the turbine wheel 14 that defines the mass flow.

Various possibilities for regulating the mass flow exist.

According to a first embodiment as shown in figure 4 the turbine wheel 14 is used in locked condition whereby the force 55 or the torque needed to lock the turbine wheel 14 serve as a signal to control the dosing valve 6. The force or torque 55 needed,to hold the turbine wheel 14 in a fixed position counter-rotation is measured and the measurement signal is fed back to the regulating system 19 to regulate the outflow of the dosing valve 6 during use in order to keep the measured force or torque constant.

Figure 5 shows aa second aternative embodiment whereby the turbine wheel 14 is provided with a counter-rotation resistance in the form of a weak spring 56 that is mounted,between the turbine wheel 14 and a fixed point of the housing 2-49.

During use the impulse of the powder gives the turbine wheel. 14 a certain angular rotation 57 against the spring force which, is proportional to the collision force of the powder.

Said. angular rotation 57 is then measured and used as measurement signal for controlling the dosing valve 6 to keep the angular rotation 57 constant,during use by regulating the outflow of the dosing valve 6.

A third and most preferred embodiment is shown in figure 6 whereby in this case the turbine wheel 14 is freely rotatably bea ring-mounted in the housing.

Under impulse of the powder the turbine wheel starts to rotate, it. accelerates until the counteracting air friction and the bearing friction,in the bearing 48 cause a balance condition , whereby the speed of rotation 54 of the turbine wheel 14 can obtain a constant value by regulating the dosing valve 6.

Said speed of rotation 54 of the turbine wheel 14 is proportional to the mass flow as explained below. Said constant speed of rotation 54 of the turbine wheel 14 can be influenced by the tangential speed 53 with which the powder- air-mixture leaves the distribution wheel 9 but it is kept constant because the speed of rotation 59 of the distribution wheel is kept constant.

Said constant speed of rotation 54 of the turbine wheel 14 is also influenced by the increasing air friction at increasing speeds of rotation and the bearing friction in the bearing 48 of the turbine wheel 14.

However, air and bearing frictions can be considered over shorter or longer periods as a stable given and the stability thereof can furthermore be monitored over the further progress of the process.

Said constant speed of rotation 54 of the turbine wheel 14 is consequently exclusively influenced by tthhee powder mass dispersed by the dosing valve 6 all.around in the distribution wheel 9.

Consequently it can be stated that the speed of rotation 54 of the turbine wheel 14 is proportional to the mass flow that is regulated by the dosing valve 6 according to the aforementioned formula whereby F is the force that drives the turbine wheel, Q is the mass flow and v is the peripheral velocity 53 of the distribution wheel 9.

The speed of rotation 54 of the turbine wheel 14 is measured with a speed sensor 18 which is shown in figures 3 , 7 and 8. By means of a regulating system 19, shown in figure 2 the dosing valve 6 can ensure that a speed of rotation of the turbine wheel 14 and consequently also the mass flow at the outlet: 17 of the turbine wheel 14 is kept constant by allowing more or less powder to pass.

The thus dosed powder flowing out of the turbine wheel 14 is collected by a funnel 49 and discharged at the bottom via an exit 5.

The speed of rotation of the turbine wheel 14 to be set for obtaining a desired mass flow at the exit 5 can be experimentally defined in advance as follows by means of external gain in weight scales (not shown) which measure the gain in weight over time. Said. external scales do not necessarily belong to the dosing device.

When said speed of rotation 54 is known , the regulating system

19 can ensure that said speed of rotation 54 remains constant by adjusting the speed of rotation of the dosing valve 6 such that the desired constant mass flow is achieved,at the exit 5.

Subsequently , the external scales 21 are removed or switched off and the dosing device 1 is ready for dosing.

It then suffices ttoo supply and add powder continuously to always have powder in the inlet 4 between a minimum,and maximum level as shown in figure 2.

By then driving the distribution wheel 9 at a constant speed of rotation, powder with a constant mass flow will be supplied at the exit 5. Although good results can be achieved with this basic embodiment , a self-adjusting embodiment of a dosing device 51 is described hereafter as an addition to the basic embodiment with which the speed of rotation of the turbine to be set at the start-up is automatically set without the need of manual actions and/or separate scales and without the need to separately discharge the mass powder required in the basic embodiment to adjust the dosing device 1 such that the spread of dust can be avoided and the dosing device can also be used, for dustproof systems and in case of highly toxic powders.

An example of such self-adjusting embodiment of a dosing device 51 according to the invention is shown in figure 16 whereby the basic embodiment of figure 1 is additionally provided,with built-in gain in weight scales 22 , this in combination with a diverter valves system with valves 27-28 -29.

The desired mass flow is entered in said dosing device 51 at the start-up, after which the device will set itself to this value and whereby the mass flow is only guided to the end exit 5 when the desired,value is achieved.

As shown in figure 16, the dome-shaped lid 2 with distribution wheel 9 and turbine wheel 14 and dosing valve 6 with said,self- adjusting dosing device 51 is mounted on top of a double funnel 23 which is provided with a. distribution valve 24 shown in figures 11 to 15 and with which the powder flow, which on leaving the turbine wheel 14 falls down homogenously distributed along the contour of the dome-shaped lid 2 , can be adjustably divided in a dosing flow and a parallel residual flow which have a constant ratio relative to each other at all times. Consequently, the double funnel 23 has an exit 26 at the bottom for the dosing flow that will go to the exit 5 and an exit 25 for the parallel flow which can be automatically recovered further on.

As shown in figures 11 to 15, the distribution valve 24 is rotatable around the central shaft and is set manually or via an algorithm such that, the dosing valve 6 is able to always function in the optimum part of its operating area during'the supply of a set mass flow at the funnel exit 26.

Consequently, the operating area of the dosing device 51 is extended downward such that it can also be used for the precise dosing of very small mass flows.

Figure 13 shows the distribution valve 24 in a position corresponding with a ratio of approximately 15%-85%, whereas in figure 14 the distribution valve is rotated to a 50%-50% ratio position.

Both powder flows depart from a powder that is uniformly distributed at the contour of the turbine wheel 14 and ends up in the funnel 23 under the influence of gravity , such that both flows are also dosed in a fixed ratio at the exits 25 and

26.

As appears from the figures 16 to 19 the exits 25 and 26 of the double funnel 24 connect to diverter valves 27 and 28.

The diverter valve 28 connects to the dosing exit 26 and is connected to built-in gain in weight scales 22 via a Y-piece 33 with a diverter valve 29 therein. Depending on the positions of the valves 28 and 29 to be set, the dosing flow ccaann be transported directly to the exit 5 during operation as shown in figures 17 and 19 or diverted alternatively to the scales 22 as shown in figure 18 for defining the speed, of rotation of the turbine wheel 14 upon adjustment during the start-up procedure as explained above.

The diverter valve 27 connects to the parallel exit 25 of the double funnel and is directly connected via a bypass 34 to the collector 36 for recovery of the parallel flow during the start-up procedure as shown in figure 18 or via the Y-piece 33 and diverter valve 29 to the built-in gain in weight scales 22 during operation as shown in figure 19.

Preferably, the parallel flow coming from the diverter valve 27 can be transported to the built-in gain in weight scales 22 after the start-up procedure as shown in figure 1.9 because the tables generated therewith during operation must remain unchanged and can thus detect, irregularities in connection with the air friction or the bearing friction of the turbine wheel 14, the speed of rotation of which defines the accuracy of the dosed mass flow.

The diverter valve 29 also allows the entire mass flow of the dosing device 51. to be utilised by guiding both powder flows during the start-up procedure to the built-in gain in weight scales 22 to subsequently send the entire mass flow on to the end exit 5 as shown in figure 17.

As shown in more detail in figure 20 the built-in gain in weight scales 22 substantially contain an open collection jar 30 mounted to a shaft coupling 61 with pivotal point 58 which can be tilted by means of a drive 32 to empty the collection jar without thereby interrupting the powder flow .

The operation of the pivotal point 58 allows the collection jar 30 to be supported on a load cell 31 which measures the gain in weight of the received powder over time.

The aforementioned regulating system 19 compares said measurements with the desired situation.

During the start-up procedure of"figure 18, the collection jar 30 receives the dosing flow via the diverter valve 28 which is gradually increased by the dosing valve 6 until the gain in weight measurements show that the desired mass flow is achieved and consequently the governed speed of rotation 54 of the turbine wheel 14 is also known.

The mass flow is controlled after the start-up procedure by keeping the speed of rotation of the turbine wheel 14 constant.

From that moment deviations in the gain in weight of the load cell 31 can point to changes in the friction of the turbine wheel 14 such that the regulating system 19 can change the governed,speed of rotation of the turbine wheel 14 or issue an error message if necessary.

The collector 36 is a buffer tank at the bottom that collects powder coming from the built-in gain in weight scales 22 , from the bypass 34 and preferably also freshly supplied new powder via channel 35. Further, a return system.39 is also connected to the collector 36 with which the unused powder can be transported back to the supply pipe 46 at the top via a return system 39 as shown in figure 16.

Preferably, the powder coming from the built-in gain in weight scales 22 and the powder that ends up in the collector 36 via the bypass 34 for return to the supply pipe 46 needs to receive priority over the new powder from the channel 35.

Said priority can be obtained by, for example, making the inclination of the supply 35 of the new powder to the collector 36 less steep than the inclination that:the already used powder from the scales 22 oorr the bypass 34 follows to the return system 39.

New powder can consequently only flow into the collector 36 via the channel 35 when the powder level has dropped to below the exit of the channel 35 in the collector 36.

In addition, the collector 36 is also provided with a valve 43 at the bottom,that can be used to empty the whole dosing device 51 and which is also functional when WIP or CIP cleaning is applied.

The return system 39 can consist", of a vertical return pipe 40 which contains a coaxial Archimedes screw 41 that can have a drive 44 at the top and the end 42 of which is located at the bottom in the collector 36. Said end 42 of the Archimedes screw 41 can, for example, be an enlargement of the screw diameter to make vertical transport of powder from the collector 36 possible.

At the top the return system 39 ends in the supply pipe 46 whereby the powder is dropped in the supply pipe 46 at a position 60 above a sensor 45 which detects the highest permitted powder level.3.

When said level is achieved, the supply system 39 stops supplying powder.

There may also be a second level sensor 48 in the supply pipe 46 which detects the lowest permitted powder level 3 and consequently gives the start signal for the supply system 39.

The embodiment, of the return system 39 is not limited to a return pipe 40 with an Archimedes screw 41.but it can also be executed as pneumatic transport bucket elevator or other known transport systems.

Figures 21 and 22 show a more compact embodiment of a dosing device 52 according to the invention whereby the return pipe 4 0 with the Archimedes screw 41 is centrally mounted, coaxially with the distribution wheel 9 whereby the Archimedes screw 41 takes over the function of dosing valve 6 when the powder that is transported upwardly by the Archimedes screw 41 leaves the return pipe 40 at the top on the level of the distribution wheel 9.

In that case the supply pipe 46 with the sensors 45 and 48 and also the entry 4 with the separate dosing valve 6 are omitted and the speed of rotation of the Archimedes screw 41 is regulated by the regulating system 19 to come to a constant speed of rotation 54 of the turbine wheel 9 and thus achieve a constant mass flow at the exit 5 in the same way.

The present invention is by no means limited to the embodiments described as an example and shown in.the drawings, but a dosing device according to the invention can be realised in all kinds of forms and dimensions, without departing from the scope of the invention.