Apparatus for separating fine solid particles from waste water

In a centrifuge device whose purpose is in particular the separation of amalgam from waste water generated in dentist' offices, the following is provided in order to improve the determination of the filling level in a collecting tank downstream from a centrifuge, to obtain better utilization of the container volume, to reduce the residual moisture in the separated solids, and to simultaneously eliminate the repumping means which operate between the collecting tank and the centrifugal. The collecting tank is detachably attached to a centrifuge drum and rotates together with the centrifuge, with measures being taken for separating the clean-water space from the centrifuge drum, there is also provided a transport container which can be detached from the device together with a collecting tank, which container can, when the collecting tank is in it, be closed by means of a cover which, when it is not in use, is detachably attached to the transport container. The device can also be designed in such a manner that a liquid/gas/solids mixture, generated, for example, in the oral cavity of a dentist's patient, can be fed to it simultaneously for the purpose of phase separation.

The invention relates to a device for separating fine solid particles from 
waste water, in particular amalgam particles from the waste water of a 
dentist's office. Such devices including a centrifuge drum surrounding by 
a housing, the drum having a peripheral wall, a conic drum bottom having a 
central orifice and being connected to the drum wall so as to project 
downwardly and a ring-shaped barrier flange carried by the upper free end 
of the peripheral wall of the drum so as to extend radially inwardly and 
form a limit of an overflow opening through which the inside of the 
centrifuge drum communicates with a discharge space for clean water, which 
space is located in said housing. A drive shaft of a motor is attached to 
the housing, which drive shaft carries the centrifuge drum, and an inlet 
tube which surrounds the drive shaft concentrically at radial distance, is 
firmly attached to the housing, passes through the overflow opening with 
radial play and communicates with a duct located in the housing for intake 
of waste water, and with the interior space of the centrifuge drum. A 
collecting tank for the separated solid particles is detachably attached 
and communicates through the orifice with the interior space of the 
centrifuge drum. 
In known devices of this kind (e.g. German Disclosure Document No. 35 42 
115, FIG. 7) the collecting tank for the solid particles is connected to 
the housing in such a manner that, when the centrifuge drum is standing 
still, it is filled, through the central orifice in the bottom of the 
drum, with separated solid particles, starting at the center of the tank. 
This results in poor utilization of the storage volume provided in the 
collecting tank. In addition, in the known devices it is necessary to 
provide special means at the lower end of the hub of the centrifuge for 
pumping the water flowing into the collecting tank back into the 
centrifuge drum when the centrifuge is started. Another source of 
difficulties in the known devices is the collecting of information on the 
filling level of the collecting tank, because reliable information 
requires sufficient sedimentation of solid particles in the collecting 
tank. 
It is the purpose of the invention to provide a device of the 
above-mentioned type, in which the utilization of the storage volume of 
the collecting tank and the collection of information on the filling level 
are improved while at the same time no special means for pumping the water 
from the collecting tank are required. 
This object is achieved by a device of the above-mentioned type wherein the 
collecting tank is detachably and in a sealed manner attached to the 
centrifuge drum in such a manner that it cannot rotate relative to same, 
and the barrier means is provided with separate housing space adjoining 
the external periphery of the peripheral wall of the drum from the 
discharge space for clean water. 
According to the basic idea of the present invention, the collecting tank 
participates in the rotation of the centrifuge drum, so that the 
centrifugal force will act also on the separated solid particles, which 
have entered the collecting tank under the influence of gravity while the 
centrifuge drum is standing still, and on the water in the tank. The 
separated solid particles are therefore deposited in a ring-shaped manner 
on the inner wall of the rotating collecting tank, with the layer 
thickness increasing with operating time, while the water entering the 
collecting tank also forms a ring on the inside whose thickness is limited 
by the diameter of the central orifice in the bottom of the drum. An 
excess of water is pushed upwards through the orifice into the centrifuge 
drum as a result of centrifugal force and without any additional pumping 
or similar equipment being required. In this manner a well-defined laminar 
structure of the separated solid particles in the collecting tank, and 
consequently a good utilization of its storage volume, are achieved. The 
well-defined laminar structure also makes it much easier to obtain exact 
information on the filling level. In addition the layer of solid particles 
precipitated in the collecting tank is greatly densified and as a result 
the residual moisture in the sediment is low, which in turn facilitates 
recovery of the precipitated solids. The barrier means ensure when the 
centrifuge is in operation and also when it is standing still that clean 
water from the discharge space cannot flow to the exterior of the 
centrifuge drum. 
By placing the collecting tank within a transport containers which 
surrounds the collecting tank so as not to touch it and which has an 
opening by which it is attached to the housing in a sealed and detachable 
manner, it is ensured in an advantageous manner that the collecting tank 
participating in the rotation is covered toward the outside by the 
transport container which does not participate in the rotation, and that 
after it has been replaced and its contents are protected for 
transportation to a waste treatment facility. The seal between housing and 
transport container ensures that any clean water which, in spite of the 
barrier means, penetrates into the housing space at the outside wall of 
the drum cannot escape to the outside from the device. 
In order to detachably fasten the collecting tank and the centrifuge drum 
to each other, a screw connection may be established between these parts, 
but preferably a bayonet lock is used which can be unlocked by lifting and 
rotating the collecting tank. This design also offers, together with a 
bayonet lock for attaching the transport container to the housing the 
advantageous possibility to detach the collecting tank and the transport 
container simultaneously and jointly from the device. All that is required 
for this purpose is to lift and rotate the transport container. When this 
is done the bayonet locks of both containers are released so that both 
containers can be pulled out downwards to release the engagement with the 
housing and the centrifuge drum, respectively. 
By providing a catch for the lock of the transport container, it is ensured 
that it is impossible to bring the transport container inadvertently into 
a position which permits lifting. The catch provided here locks the 
transport container in a defined position on the housing. 
In a further embodiment, a cover is provided for closing the transport 
container with the collecting tank inside. A convenient storage is 
provided for the cover when it is not in use. 
In yet another embodiment a seal is provided in an advantageous manner on 
the collecting tank for sealing the collecting tank against both the 
housing and the cover when it is in place. 
In an advantageous further development of the invention the barrier means 
which separate the discharge space containing the clean water from the 
housing space adjacent to the peripheral wall of the drum and thus also 
from the gap space between the collecting tank and transport container has 
at least one closed ring-shaped wall which is concentric with the 
centrifuge drum and protrudes upwards from the bottom surface of the 
discharge space for clean water, and at least one circle, also concentric 
with the centrifuge drum, of vanes which are radially oriented and adjoin 
the ring-shaped wall in such a manner that a narrow gap is formed. The 
barrier flange also extends radially outwards from the peripheral wall of 
the drum beyond the ring-shaped wall, of which at least one is present, 
and the vanes are attached to the barrier flange in such a manner that 
they protrude downwards. When the centrifuge drum rotates the vanes 
participate in this rotation with the same angular velocity because they 
are fastened to the barrier flange and move the clean water discharged 
from the overflow opening radially outwards, thus creating an effective 
dynamic seal. When the centrifuge stands still the ring-shaped wall acts 
as a barrier wall within the discharge space and prevents the clean water 
from flowing in the reverse direction, even if the water level in the 
discharge space is high. 
Useful embodiments of the barrier means discussed above include: (1) two 
ring-shaped walls and two circles of vans engaged therewith; (2) one 
ring-shaped wall having outer steps, and vanes with a corresponding step 
shape; and, (3) vanes extending to the peripheral wall of the drum. 
In further pursuit of the idea of the invention, the desirable possibility 
to determine the exact filling level in the collecting tank which is 
offered by the invention is put into practice by providing at least two 
channels on the collecting tank which are positioned opposite each other 
in pairs, are directed inwards, have identical dimensions and consist of 
material which is transparent to light. If desired, the transport 
container is transparent to light in at least two areas located opposite 
each other and, in a manner known per se, a light-sensing system is 
fastened to the frame of the centrifuge for the purpose of determining the 
filling level, with the optical axis of said light-sensing system being 
lined up with said channels. Here the depth of the channels determines the 
permissible level in the collecting tank, i.e. the permissible thickness 
of the layer of solid particles which have been separated and deposited on 
the wall of the collecting tank by the action of the centrifugal force. As 
soon as the layer has become so thick that the opposing surfaces of the 
channels are covered by solid particles an optical and/or acoustic signal 
is triggered with the aid of the electric eye, which indicates that the 
collecting tank has to be replaced. 
Instead of or in addition to the above-described level measurement by means 
of a sensor, it is also possible, in further pursuit of the idea of the 
invention, to determine the filling level, by evaluating the starting 
torque of the motor, which is made possible by the fact that the 
collecting tank participates in the rotation. 
As a result of the choice of the inside radius of the collecting tank to be 
greater than the inside radius of the peripheral wall of the drum the 
sediment is densified even more because of the comparatively higher 
circumferential velocity at the collecting tank wall and the resulting 
stronger action of the centrifugal force on the separated solids. 
In a further embodiment of the device according to the invention, this 
device is designed in such a manner that liquid/solids mixtures and 
liquid/gas/solids mixtures can be fed to it simultaneously in order to 
separate the solid particles and the gaseous phase from liquids. In this 
design even large quantities of liquid do not cause a shut-off of the gas 
exhaust of the device and no complicated valve control systems are 
required. With regard to the preferred use of the device in dentists' 
offices this means that the device can be used to receive and process the 
contaminated waste water from the cuspidor bowl, which contains solids, 
and simultaneously process the liquid/gas/solids mixture sucked from the 
oral cavity, for the purpose of separation or phase separation, 
respectively. 
This is achieved by providing a suction tube concentrically with the drive 
shaft and permanently attached to the housing, whose lower open end 
extends into the centrifuge drum and forms the limit of a suction space 
surrounding the drive shaft, which space can be connected to a source of 
reduced pressure. A separating tube is provided between the suction tube 
and the inlet tube and concentrically to them, which is located in the 
housing and attached to the centrifuge drum in such a manner that it 
cannot rotate relative to the latter, whose upper open end communicates 
with the intake duct for a liquid/gas/solids mixture, whose lower open end 
extends into the centrifuge drum and which forms, together with the 
suction tube, a ring-shaped space. The upper end of the separating tube 
passes rotatably through a sealing ring fastened to the housing which 
seals the intake duct for waste water against the intake duct for 
liquid/gas/solids mixtures. The separating tube comprises at its lower end 
a separating flange extending outwards which, when the centrifuge is in 
operation, dips with its entire periphery into a liquid layer formed on 
the peripheral wall of the drum. In the device according to this design 
the sucked-off liquid/gas/solids mixture is separated into a liquid/solids 
phase and a gaseous phase by the centrifugal action of the separating tube 
which participates in the rotation and which seals off, by means of the 
separating flange dipping into the water ring of the centrifuge drum, the 
space in which the pressure is reduced from the outside pressure. The 
liquid/solids phase flows downwards along the inner wall of the separating 
tube and then outward along the separating flange and then flows into the 
water ring of the centrifuge drum from which the solids move to the 
peripheral wall of the drum, while the liquid phase flows, past the 
barrier flange with a weir-like action, into the discharge space for clean 
water. The gaseous phase, on the other hand, is pushed toward the center 
of rotation and flows downwards along the suction tube until it is 
deflected by 180.degree. at the lower end of said tube and enters the 
exhaust space. 
Due to the design of the device in accordance with the invention, the 
gaseous phase is reliably separated and discharged through the source of 
reduced pressure, even if large volumes of waste water arrive 
simultaneously in the device, particularly if the cuspidor bowl is emptied 
and/or from the suction system. 
By having the suction tube communicate at its upper end with a suction duct 
tangentially connected to the suction space, the formation of a gas 
cyclone in the exhaust space is assisted. Small drops of liquid carried 
along by the gas flow are separated from the gas flow by the cyclone 
effect at the point where the 180.degree. deflection takes place and are 
carried outwards outside, away from the center of rotation. 
By providing several acceleration vanes at equal distances from each other 
in a ring-shaped space between the suction tube and the separation tube, 
which vanes are attached to the separation tube and extend radially to a 
point at a distance from the suction tube, and connecting the intake duct 
for the liquid/gas/solids mixture tangentially to the ring-shaped space 
between the suction tube and the separating tube the separating action of 
the device for liquid/gas/solids mixtures coming from the suction system 
is increased. 
In a further embodiment, the accelerating vanes are made in one part with 
guiding vanes which connect the centrifuge drum with a hub sleeve placed 
on the drive shaft in such a manner that these parts cannot rotate in 
relation to each other. 
In still another embodiment, the intake duct for waste water is 
tangentially connected to a ring space-shaped inlet chamber whose outside 
limits are formed by the housing and the inlet tube. 
In yet an additional embodiment, the inside limits of inlet chamber are 
formed by the separating tube which passes through it coaxially. 
In a further design of the device a separating flange divides the 
centrifuge drum into two sections, one above the other, the upper one of 
which is used for separating the solids from the waste water, while the 
lower one is used for separating the solids from the liquid carried along 
by the exhausted liquid/gas/solids mixture. Accordingly, the upper section 
is under the same pressure as the surroundings, while the pressure in the 
lower section is reduced. When the centrifuge drum stops the pressures are 
equalized. The separated solids coming from the upper and lower section 
are carried downwards through the orifice in the centrifuge drum by the 
action of gravity. 
In still a further arrangement, the housing is composed of a lower housing 
and an upper housing, with the lower housing comprising the inlet chamber 
for waste water, the inlet tube, the intake duct for waste water, the 
discharge space for clean water and the centrifuge drum with the 
separating tube, while the housing comprises the suction duct, the intake 
duct for the incoming liquid/gas/solids mixture and the suction tube 
protruding therefrom, and the drive shaft and the hub sleeve pass through 
the upper and lower housings, with the hub sleeve passing through a 
housing seal in the upper housing, which seals off the reduced pressure 
from the outside. 
In a further embodiment the intake duct for waste water, one discharge duct 
for clean water, the suction duct and the intake duct for the 
liquid/gas/solids mixture all lead, one above the other, to one side of 
the device, this further improves the compactness of the device according 
to the invention and makes it easier to connect the devices to the 
corresponding piping. 
In an additional arrangement the suction tube in the area of the intake 
duct for the liquid/gas/solids mixture is closely surrounded by an 
enveloping tube whose lower end extends into the ring-shaped space between 
the suction tube and the separating tube and is connected through the 
accelerating vanes with the separating tube in such a manner that it 
cannot rotate in relation to the latter. This further improves the 
separating action of the device for sucked-off liquid/gas/solids mixtures 
because immediately after entering the device the mixtures make contact 
with the cover tube which rotates at the same speed as the centrifuge and 
flings the mixture toward the outside as seen from the center of rotation. 
It is therefore completely impossible for the liquid and solid parts of 
the mixture also to flow along the suction pipe, as the entering mixture 
is immediately repelled by the rotating cover tube and transferred to the 
rotating separating tube which effects separation of the gaseous phase. 
This design ensures that the gaseous phase exhausted from the device is 
completely dry. 
When the ring-shaped space is designed in such a manner that between the 
suction tube and the separating tube its cross section continually 
decreases in the flow direction of the liquid/gas/solids mixture, a nozzle 
effect is created in the ring-shaped space for the liquid/gas/solids 
mixture, i.e. the flow is accelerated.

The device shown in FIG. 1 for separating amalgam particles from the waste 
water generated in a dentist's office is, to the left and the right of the 
centerline of the device and in a manner which will be described below, 
partly designed differently and partly shown in different positions. The 
housing of the device carries as a unit the reference numeral 10, while 
the centrifuge as a unit is carrying reference numeral 11. 
Intake fitting 13 is attached to intake duct 12 which is located in housing 
10 in a direction transverse to the centerline of the device. Ring-shaped 
discharge space 14 for the clean water coming from centrifuge 11 is 
located below intake duct 12, and discharge fitting 15 is attached to said 
discharge space 14. As shown in FIG. 2, intake duct 12 leads tangentially 
into inlet chamber 16 which is concentric with the centerline of the 
device and to which is connected inlet tube 17 leading downwards. Inlet 
tube 17 forms the inside limit of ring-shaped discharge space 14 and 
reaches into casing wall 18 of housing 10, which casing is concentric with 
the centerline of the device and essentially encloses centrifuge 11. 
An external ring-shaped wall 19 which extends further downward is provided 
on the housing at a radial distance from the cylindrical casing wall 18. 
Said wall 19 forms the outer limit of the ring-shaped receiving space 20 
which is open toward the bottom and whose inner limit is formed by casing 
wall 18. The upper end of transport container 21, which is detachably 
fastened to housing 10 in a manner described below, extends into receiving 
space 20. Transport container 21 has the shape of a cylindrical cup and 
carries on the edge of its opening the lip seal 22 which makes contact 
with the cylindrical outer surface of casing wall 18 in such a manner that 
a seal is formed but that said lip can be moved up and down, as is shown 
by a comparison of the left and the right half of FIG. 1. 
Electric motor 23 is attached by a flange to the top of housing 10 in such 
a manner that its principal axis is in line with the centerline of the 
device. Drive shaft 24 of electric motor 23 passes through housing seal 25 
and ends below inlet tube 17. Drive shaft 24 carries in the manner 
described below a centrifuge drum which is attached to it in such a manner 
that it cannot rotate in relation to said shaft. The complete centrifuge 
drum is designated by reference numeral 26. 
Centrifuge drum 26 comprises peripheral wall 27 and conical bottom 28 which 
adjoins said wall at its lower edge, with said bottom ending in orifice 
29. Orifice 29 is of circular shape and concentric with the centerline of 
the device. At the free end of peripheral wall 27 of the drum and attached 
to it firmly and tightly, and for example forming one piece with it, there 
is located barrier flange 30 in the shape of a circular ring which on the 
inside forms the limit of overflow opening 31, also in the shape of a 
circular ring. The outside surface of inlet tube 17 forms the inner limit 
of overflow opening 31. Barrier flange 30 also extends radially outward 
from peripheral wall 27 of the drum in order to permit the placement of 
barrier means which will be explained in detail below. These barrier means 
are shown with different shapes in the left and right halves of FIG. 1 and 
carry reference numerals 32 and 32'. By means of a plurality of radially 
oriented guiding vanes 33, centrifuge drum 26 is rigidly attached to hub 
sleeve 34 which is slid onto drive shaft 24 and fastened to the latter by 
screw 35 so that centrifuge drum 26 and all parts rigidly attached to it 
are carried by drive shaft 24 in such a manner that they cannot rotate 
relative to said shaft. FIGS. 1, 3 and 4 show that the guiding vanes 33 
extend between the inner surface of peripheral wall 27 of the drum and the 
hub sleeve. In the embodiment shown the vanes are L-shaped and end with 
the inner surface of their vertically upward-pointing tab at the edge of 
overflow opening 31. Their horizontally oriented tab is located closely 
below the edge of the opening of inlet tube 17. 
Collecting tank 36 which has the shape of a cylindrical cup is detachably 
fastened to the lower end of centrifuge drum 26, with sealing ring 37 
inserted and in such a manner that it cannot rotate relatively to said 
drum. In order to establish a detachable fastening which prevents relative 
rotation, several, for example four, bayonet locks are provided along the 
periphery, with two bayonet pins attached to peripheral wall 27 of the 
drum being visible in FIG. 1. The bayonet pins 38 cooperate with bayonet 
slots 39 located in the edge area of collecting tank 36, with one of these 
slots being shown in FIG. 10. Collecting tank 36 is attached to the 
centrifuge drum by pushing the bayonet slots with their slot section 
opening toward the top onto the bayonet pins 38 until the bayonet pins 
reach the horizontal part of the bayonet slots. The bayonet lock is then 
locked by rotating collecting tank 36 to the left until the bayonet pins 
can enter the shorter sections of the slot which point in the vertical 
direction and are closed at the top. After collecting tank 36 has been 
moved slightly downwards it is attached to centrifuge drum 26 in such a 
way that it cannot rotate relative to the latter. 
The left half of FIG. 1 shows collecting tank 36 and the transport 
container 21 which surrounds it on all sides without touching it, in the 
position they have when the centrifuge is operating. The right half of 
FIG. 1 shows, on the other hand, the relative positions of transport 
container 21 and collecting tank 36 during the operation to be described 
below in which both containers are jointly detached from the device. Here 
transport container 21 is shown in the raised position. 
Transport container 21 is detachably fastened to housing 10, also by means 
of a bayonet lock. For this purpose several bayonet pins 40 are attached 
in the embodiment shown to the periphery of transport container 21 which 
engage bayonet slots 41 provided in ring-shaped wall 19. The shape of the 
bayonet slots 41 is shown in FIG. 9. When transport container 21 is 
attached to housing 10, the bayonet pins 40 first enter the shorter 
sections of the bayonet slot, which are open toward the bottom, one of 
which is shown on the left side of FIG. 9. Now transport container 21 is 
lifted until the bayonet pins 40 reach the longer of the two horizontal 
slot sections. When the transport container is rotated toward the right 
the bayonet pins 40 move in this horizontal part of the slot until they 
reach the catch recesses 42 one of which is shown in FIG. 9. In this 
position transport container 21 is held in a fixed position relative to 
housing 10 by the bayonet pins 40 which engage the catch recesses 42 and 
form, together with said catch recesses 42, a lock against rotation. The 
rotational lock can be released by slightly lifting and turning the 
transport container 21. 
In order to be able to detach transport container 21 and collecting tank 36 
jointly from housing 10, it is necessary to have both containers engage 
each other in such a manner that they cannot rotate against each other. At 
least one stop 50 is provided for this purpose on collecting tank 36 and 
at least one counterstop 51 on transport container 21 is associated with 
it. When transport container 21 is lifted into the position shown in the 
right half of FIG. 1, stop 50 and counterstop 51 are engaging each other 
in such a manner that when the two containers are rotated toward the right 
they are simultaneously released from the bayonet lock in question. 
If the two containers are to be removed, transport container 21 is first, 
by rotation to the right, moved from its rotary catch position. By this 
movement the bayonet pins 40 are removed from the corresponding catching 
recesses of the bayonet slots 41. The rotation of the transport container 
21 toward the right is continued until the bayonet pins 40 are located 
opposite the vertical short slot sections at the center, which connect the 
two horizontal slot sections of the bayonet slots 41 with each other. Now 
transport container 21 is lifted, with the bayonet pins 40 moving upwards 
in the corresponding short sections of the slots. During this operation 
stop 50 and counterstop 51 become engaged. In the last phase of the 
upwards motion, collection tank 36 is taken along in the upward direction, 
with its bayonet slots 39 being shifted upwards in relation to the 
stationary bayonet pins of centrifuge drum 26. At the end of the upward 
motion of the two containers 21 and 36 the bayonet pins 40 and 38, 
respectively, associated with each container, are located opposite 
horizontal slot sections. When transport container 21 and collecting tank 
36, connected to it in such a manner that relative rotation is excluded, 
are rotated further toward the right, the bayonet pins 38 and 40 finally 
move into the vertical slot sections which are open toward the top and the 
bottom, respectively, and the two containers can then be jointly pulled 
off downwards. 
For closing transport container 21 there is provided cover 52 comprising at 
its edge bayonet slots 53 which are designed in such a manner that they 
can engage the bayonet pins 40. The engagement is arranged in such a way 
that cover 52 which has been placed on top [of the container] and locked 
in place sits tightly on lip seal 22. For storing cover 52 on transport 
container 21 when the cover is not in use, bayonet pins 54 are provided on 
the outside of the transport container near the bottom which cooperate 
with the bayonet slots 53. 
In order to describe in detail the barrier means which prevent clean water 
from penetrating from discharge space 14 into the gap-shaped part of the 
housing which adjoins the housing periphery of peripheral wall 27 of the 
drum and is indicated by reference numeral 55, we are now referring to 
FIG. 1 together with FIGS. 5 to 8. The gap-shaped housing space 55 is in 
communication with the gap-shaped space between transport container 21 and 
collecting tank 36. In order to establish a barrier it is provided in all 
embodiments that the cylindrical inside surfaces of casing wall 18 
continue in and are in line with a closed ring-shaped wall 56 or 56', 
respectively, which extends toward the top into discharge space 14 up to a 
point closely below barrier flange 30 of centrifuge drum 26. In the left 
half of FIG. 1 and in the embodiments according to FIGS. 5, 7 and 8 an 
additional ring-shaped wall 57 is provided in addition to ring-shaped wall 
56 at a radial distance from ring-shaped wall 56. Ring-shaped wall 57 
extends upwards from bottom 58 of discharge space 14 and also ends closely 
below barrier flange 30. Ring-shaped wall 56' shown in the right half of 
FIG. 1 is designed as a ring-shaped wall with external steps, as is the 
embodiment shown in FIG. 6. 
At least one circle of radial vanes extending downwards is fastened to 
barrier flange 30. In the embodiment according to the left half of FIG. 1, 
which is very similar to the embodiment according to FIG. 5, two sets of 
vanes 59 and 60 or 60', respectively, are provided. In the embodiment 
according to the right half of FIG. 1, which corresponds to the embodiment 
according to FIG. 6, only one set of vanes 61 is attached to barrier 
flange 30, with the vanes 61 being designed with steps matching 
ring-shaped wall 56'. In the embodiment according to FIG. 7 two sets of 
vanes are provided in principle; the vanes extend, however, downwards from 
a transverse part with which they form one piece and which extends as far 
as the peripheral drum wall 27. All the vanes according to FIG. 7 are 
given the reference numeral 62. The ring-shaped walls 56, 56' and 57 and 
the vanes 59 to 62 are in each case in such a position relative to each 
other that narrow gaps are formed between them. 
The ring-shaped walls 56, 56' and 57 ensure that water which is still 
present in discharge space 14 when the centrifuge is standing still cannot 
penetrate into housing space 55 or between the walls of the two containers 
21 and 36. When the centrifuge is in operation the vanes 59 to 62 form a 
dynamic seal because they ensure that the clean water emerging from the 
centrifuge is moved radially outward by centrifuge drum 26. 
FIG. 7 shows that peripheral wall 27 of the drum can be covered on the 
inside with a coating 63 protecting it against wear. 
FIGS. 11 to 14 show how an infrared light sensor can be provided for 
indicating the filling level in collecting tank 36. For this purpose two 
diametrically opposed channels 64 which are directed inwards and have 
identical dimensions are provided in collecting tank 36. In the position 
of the parts shown in FIG. 11 IR light source 65 is positioned opposite 
one channel 64 and IR sensor 66 is positioned opposite the other channel 
64. Light source 65 and sensor 66 are fastened to centrifuge frame 67 in a 
suitable manner so that they are stationary. Their joint optical axis is 
directed toward the channels 64, i.e. it intersects the centerline of the 
device. The entire collecting tank 36 and the entire transport container 
21 may consist of material which is transparent to infrared light. It is, 
however, sufficient if the opposed surfaces of the channels 64 on 
collecting tank 36 as well as the areas of the wall of transport container 
21 which are located opposite light source 65 and sensor 66 are 
transparent to IR light. 
It is also possible to measure the filling level by measuring the starting 
torque of motor 23, because said starting torque is a function of the mass 
of the solid particles in collecting tank 36. The curve of the torque 
during the start of motor 23 can be monitored by suitable electronic means 
and when a limit is exceeded an optical and/or acoustic signal can be 
triggered which indicates that the maximum filling level in the collecting 
tank has been reached. 
The device according to the invention functions as follows: 
The waste water from a dentist's office carrying solids flows into 
centrifuge 11 through intake fitting 13, intake duct 12 and inlet tube 17. 
It is then carried along by the guiding vanes 33 and transported along the 
vanes 33 to the inner surface of peripheral wall 27 of the drum. While 
this takes place, the solids are deposited, as is usual in such 
centrifuges, at the peripheral wall of the drum, while the water, because 
of its lower density, remains on the inside, closer to the axis of 
rotation. The ring-shaped layer of water grows toward the interior until 
it reaches the outside diameter of the overflow opening 31. Clean water 
from which the solid particles have been removed then flows continually 
through overflow opening 31 into discharge space 14 and is made to flow 
outwards by barrier flange 30 rotating with centrifuge drum 26. During 
this action the barrier means 32, 32' and 32", respectively, provide a 
dynamic seal between the space for the clean water and housing space 55. 
When the centrifuge is shut down, the deposited solids slide downwards 
along the peripheral drum wall 27 under the influence of gravity and 
continue their slide path on the conical inner surface of drum bottom 28, 
until they pass through orifice 29 into collecting tank 36. The separated 
solids discharged into collecting tank 36 and the water which has flowed 
into collecting tank 36 form two separate layers when the centrifuge is 
operating, with the solids being, of course, deposited at the wall of 
collecting tank 36, while the ring of water builds up in the inward 
direction toward the center of rotation, until the excess water can again 
flow through orifice 29 into centrifuge drum 26 from where it is directed, 
in the manner described above, as clean water into discharge space 14 
through overflow opening 31. If the layer of solids which contains only 
little residual moisture and is deposited in collecting tank 36 reaches a 
thickness exceeding the radial dimensions of the channels 64, the light 
emitted by light source 65 can no longer be received by sensor 66, and a 
signal is triggered. 
When the two bayonet locks of containers 21 and 36 are loosened, provision 
must, of course, be made to have centrifuge drum 26, and consequently its 
bayonet pins 38, held in place, so that relative rotations of the 
containers against the bayonet pins 38 are possible. This can be 
accomplished by suitable mechanical anti-rotation means acting on the 
centrifuge drum 26, but also by electrical braking of electric motor 23. 
The channels 64 required for the electric eye and sensor do not have to 
have the shape shown in FIGS. 11 to 13. It is quite sufficient if channels 
64' according to the embodiment shown in FIG. 14 are designed similar to 
cylindrical bushings and are inserted at diametrically opposed points into 
the wall of collecting tank 36. In this case, too, the opposing front 
surfaces of the channels must consist of material that is transparent to 
infrared light. 
For the explanation of the device which can, in addition, separate a 
liquid/gas/solids mixture into its three phases we are referring below to 
FIGS. 15 to 21. 
In the embodiment of FIG. 16 the cross sections shown in FIGS. 17, 18 and 
19 were also made along lines identical with the corresponding lines in 
FIG. 15. 
The device shown in FIG. 15 comprises a housing indicated by reference 
numeral 10, which consists of lower housing 10a and upper housing 10b 
which is joined to the lower housing in a manner known per se to form a 
rigid and tight connection. A centrifuge indicated by the reference 
numeral 11 is located in lower housing 10a. 
Intake fitting 13 is attached to intake duct 12 for waste water containing 
solids which is fed to the device from, for example, the cuspidor bowl of 
a dental treatment unit, with said intake duct being transverse to the 
centerline of the device. Below intake duct 12 there is located the 
ring-shaped discharge space 14 for the clean water coming from centrifuge 
11, with said discharge space being connected to discharge duct 43 for 
clean water to which discharge fitting 15 is connected. As shown in FIG. 
19, intake duct 12 leads tangentially into inlet chamber 16 which is 
concentric with the centerline of the device and to which is connected an 
inlet tube leading downwards. Inlet tube 17 forms the inside limit of 
ring-shaped discharge space 14 and reaches into casing wall 18 of housing 
10, which casing is concentric with the centerline of the device and 
essentially encloses centrifuge 11. 
Adjoining casing wall 18 is exterior ring-shaped wall 19 which extends 
further downwards and forms the outside limit of receiving space 20 
opening toward the bottom. The upper end of cylindrical transport 
container 21 extends into receiving space 20. Said container is by means 
of a screw or bayonet connection detachably fastened to ring-shaped wall 
19 and which is, in the position in which it is shown to be attached in 
FIG. 15, sealed against lower housing 10a by sealing ring 22. 
Electric motor 23 is fastened to upper housing 10b by means of a flange in 
such a way that its principal axis is in line with the centerline of the 
device. Drive shaft 24 of electric motor 23 passes through housing seal 25 
and extends through both upper housing 10b and lower housing 10a. Drive 
shaft 24 carries the centrifuge drum of centrifuge 11, which drum is 
referred to as a unit by reference numeral 26 and is attached to said 
shaft in such a manner that it cannot rotate in relation to it. Centrifuge 
drum 26 comprises a cylindrical peripheral drum wall 27 and a conical drum 
bottom 28 adjoining said wall at the bottom with said drum bottom ending 
in central orifice 29. Said orifice is of circular shape and concentric 
with the centerline of the device. 
At the free end of the peripheral wall 27 of the drum there is located 
barrier flange 30 in the shape of a circular ring whose central opening 
forms the limit of overflow opening 31, also in the shape of a circular 
ring, whose inner limit is formed by the external surface of inlet tube 
17. Barrier flange 30 extends radially toward the outside from the 
peripheral wall 27 of the drum, in order to permit positioning of the 
barrier means generally referred to under the reference numeral 32. 
Centrifuge drum 26 is rigidly connected through a plurality of radially 
directed spoke-like arranged vanes 33 with hub sleeve 34 which is placed 
on drive shaft 24 and fastened to the latter by means of threaded bolt 35 
in such a manner that centrifuge drum 26 and all parts rigidly attached 
thereto are carried by drive shaft 24 in such a manner that they cannot 
rotate in relation to said shaft. Hub sleeve 34 extends as far as the 
flange of electric motor 23 and is sealed by housing seal 25 against upper 
housing 10b . The vanes 33, in the embodiment shown in the drawing four 
vanes arranged in the form of a cross (FIG. 20), extend between the inner 
surface of peripheral wall 27 of the drum and hub sleeve 34, as shown in 
FIGS. 15 and 20. Although the section runs through a center plane of the 
device according to FIG. 15, the vanes 33, which would normally also be 
shown cut, are shown without being cut in order to more clearly 
demonstrate the design and the function of the device. Further details of 
the design of the blades 33 will be explained below. 
Threaded bolt 35 comprises collar 44 from the middle of which collar 
threaded stud 45 extends upwards and threaded stud 46 downwards, both of 
them in concentric locations. Threaded stud 45 engages interior thread 47 
at the lower end of drive shaft 24 and fastens by means of the contact 
between the collar and the lower face of hub sleeve 34 said hub sleeve and 
all parts rigidly attached to it to drive shaft 24 which engages hub 
sleeve 34 in the area of threaded stud 35 in such a manner that it cannot 
rotate in relation to said hub sleeve. Collecting tank 36 in the shape of 
a cylindrical cup comprises central stud 48 which points upwards and has 
an internal thread 49 which is used to screw collecting tank 36 to 
threaded stud 46. When collecting tank 36 is screwed onto threaded stud 
46, sealing ring 37 is placed between ring-shaped shoulder 68 of 
collecting tank 36, which shoulder protrudes toward the inside, and the 
corresponding ring-shaped surface 69 of centrifuge drum 26. This action 
seals collecting tank 36 which extends with its upper end beyond the lower 
part of circumferential wall 27 of the drum, against centrifuge drum 26. 
After collecting tank 36 has been screwed to centrifuge drum 26 in the 
manner described above, these two elements form a rotational unit which 
can be rotated by the action of drive shaft 24. If collecting tank 36 
which is filled with separated solids up to a preestablished level is to 
be emptied or replaced, said collecting tank 36 is unscrewed by suitable 
relative rotation in relation to the centrifuge drum which is held 
stationary by suitable means. Collecting tank 36 which has been unscrewed 
and is filled with solids is placed into transport container 21 which has 
previously been detached by unscrewing of screw joint 40 and for whose 
closing cover 52 is provided. Cover 52 is attached to the lower end of 
transport container 21 by a screw connection 53 or by means of a 
bayonet-type fastening. Screw joint 53 or the corresponding bayonet-type 
fastening is compatible with the corresponding screw joint 40 or the 
corresponding bayonet-type fastening, so that cover 52 for closing 
transport container 21 can be attached to the top of the latter, with 
sealing ring 22 ensuring the seal between transport container 21 and cover 
52. 
When cover 52 is not in use, it is in the position at the bottom of 
transport container 21 shown in FIG. 15. 
The barrier means 32 prevent clean water from penetrating from discharge 
space 14 into the gap-shaped housing space which adjoins the periphery of 
peripheral wall 27 of the drum and is indicated by reference numeral 55. 
The gap-shaped housing space 55 is in communication with the gap-shaped 
space between transport container 21 and collecting tank 36. Ring-shaped 
wall 56 concentrically adjoins mantle wall 18, which limits gap-shaped 
space 55 on the outside, in such a manner that it is in line with the 
continuous interior hole and extends upwards into discharge space 14 to a 
point closely below barrier flange 30 of centrifuge drum 26. Ring-shaped 
wall 56 comprises radial steps on the outside with said steps matching the 
vanes 61 which have a corresponding shape and are placed in a wreath-like 
arrangement on the underside of barrier flange 30. In this arrangement the 
blades 61 and the ring-shaped wall comprising steps are positioned in such 
a manner relative to each other, that the gaps between them are narrow. 
Ring-shaped wall 56 ensures that clean water that still remains in 
discharge space 14 when the centrifuge is standing still cannot enter 
housing space 55. When the centrifuge is running the vanes 61 act as a 
dynamic seal because they ensure that the clean water coming from the 
centrifuge is transported radially outwards. The barrier means 32 can, of 
course, also have different shapes, as shown and explained in FIGS. 1 and 
5 to 18. It is also possible, if collecting tank 36 is designed 
accordingly, to provide a level indicator device, for example an electric 
eye system sensitive to infrared, as described with reference to FIGS. 
11-14. The design of the device of FIGS. 15-21 differs from the embodiment 
described with reference to FIG. 1 in that the radial distance of inlet 
tube 17 from drive shaft 24 or from hub sleeve 34 is large enough to 
permit the placement of suction tube 70 and separating tube 71, for the 
purpose described in more detail below, between drive shaft 24 and inlet 
tube 17. 
Suction tube 70 is attached to the upper housing 10b concentrically to 
drive shaft 24 and protrudes enough from said housing that, when housings 
10a and 10b are joined, it extends into centrifuge drum 26. Suction tube 
70 limits suction space 72 surrounding drive shaft 24 or hub sleeve 34, 
respectively, and is, at its upper end, connected to suction duct 73 which 
leads tangentially into suction space 72, as shown in FIGS. 15 and 17. 
Suction fitting 74, which can be connected to a source of reduced 
pressure, is connected to suction duct 73. 
Between inlet tube 17 and suction tube 70 there is placed separating tube 
71 concentrically thereto which encloses suction tube 70 within lower 
housing 10a in such a manner that ring-shaped space 75 is formed. By means 
of the guiding vanes 33, separating tube 71 is fastened to centrifuge drum 
26 in such a manner that it cannot rotate relative to the latter. At its 
open upper end separating tube 71 is connected with intake duct 76 for a 
liquid/gas/solids mixture, which duct is located in upper housing 10b. For 
this purpose the upper end of separating tube 71 is inserted into a 
cylindrical hole 77 which is concentric with it and in which is placed 
sealing ring 78 which seals intake ducts 12 and 76 from each other and 
which, because of the rotation of separating tube 71, has the properties 
of a slip ring. Intake duct 76 leads tangentially into ring-shaped space 
75 between suction tube 70 and separating tube 71, as shown in FIG. 15 
combined with FIG. 18. Fitting 79 is attached to intake duct 76 and is 
used to connect same with a waste water feeding line, for example the 
discharge line from the cuspidor bowl. Separating tube 71 forms the inner 
limit of inlet chamber 16 for the waste water, through which chamber it 
passes coaxially. 
The lower end of separating tube 71 carries an annular separating flange 80 
which extends outwards and is very important for the functioning of the 
device. When the centrifuge is in operation, separating flange 80 dips 
with its entire periphery into liquid layer 81 which forms at peripheral 
wall 27 of the drum. Separating flange 80 which dips into liquid layer 81, 
i.e. the water ring of the centrifuge, approximately at a point close to 
the transition between peripheral wall 27 of the drum and conical drum 
bottom 28, and which can therefore be located somewhat lower than shown in 
FIGS. 15 and 16, divides the layer of liquid into an upper area and a 
lower area. These two areas can, however, communicate with each other 
underneath separating flange 80, because the peripheral surface of said 
separating flange ends radially in front of peripheral wall 27 of the 
drum. 
In the ring-shaped space 75 between suction tube 70 and separating tube 71 
there are located several acceleration vanes 33a at equal angular 
distances from each other, which are attached to separating tube 71 and 
end in the radial direction at a distance from suction tube 70, as can be 
seen from FIG. 15 in combination with FIG. 19. Four accelerating vanes are 
provided in the example shown which are designed so that each forms one 
piece with the guiding vanes 33. The lower edges of the guiding vanes 33 
are located approximately at the transition point between the peripheral 
wall 27 of the drum and the conical drum bottom 28. Their upper edges end 
in different horizontal planes. On the inside, at the hub sleeve 34, the 
adjoining upper edge of the guiding vanes 33 are located below the lower 
face of suction tube 70, without making contact. On the outside of 
peripheral wall 27 of the drum the guiding vanes 33 end below the lower 
face of inlet tube 17, without making contact. On the outside of 
separating tube 71 upwards-pointing noses 33b of the guiding vanes 33 
extend into inlet chamber 16 and end radially in front of the inner 
surface of inlet tube 17. The guiding vanes 33 and the accelerating vanes 
33a and noses 33b, which are in one piece with the vanes 33, are attached 
to peripheral wall 27 of the drum, separating tube 71 and hub sleeve 34, 
which provides for connection of all the parts which rotate when the 
centrifuge is operating. This connection is such that the above parts 
cannot rotate relative to each other. 
FIG. 15 shows that inlet duct 12, outlet duct 43, inlet duct 76 and suction 
duct 73 are located one above the other in different planes and all end at 
the same side of the device, which makes it easier to connect the device 
to the corresponding lines and contributes to the compact design of the 
device. The ducts and the fittings connected to them may be arranged 
somewhat twisted relative to the axis of rotation, in order to facilitate 
the connection of the outside lines. 
The embodiment shown in FIG. 16 differs from that of FIG. 15 only in that 
no transport container 21 is provided for collecting tank 36. Accordingly 
the casing wall 18 of lower housing 10a ends at the bottom in a plane 
surface without a protruding ring-shaped wall 19. 
The device described in relation to FIGS. 15 to 21 operates as follows: 
The waste water generated by dental activities which carries solids, and 
flows through intake fitting 13 and intake duct 12 into inlet chamber 16, 
is taken up, in inlet tube 17 which forms the lower part of inlet chamber 
16, by the noses 33b of the guiding vanes 33 and finally by the guiding 
vanes 33 themselves and transported under the influence of the centrifugal 
force along the guiding vanes 33 to the inner surface of peripheral wall 
27 of the drum. The solids are deposited here at the peripheral wall of 
the drum, as is usual in such centrifuges, while the water, because of its 
lower density, remains further to the inside, relative to the axis of 
rotation, and forms liquid layer 81 into which separating flange 80 is 
dipping. The ring-shaped layer of water builds up toward the inside until 
it reaches the outside diameter of overflow opening 31. Clean water, from 
which the solid particles have been removed then flows continually through 
overflow opening 31 into discharge space 14 and is directed outwards by 
barrier flange 30 which rotates with centrifuge drum 26. In this process 
the barrier means 32 ensure dynamic sealing of the clean-water space from 
housing space 55. In this respect the operation of the device corresponds 
to that according to FIGS. 1 to 8. 
If, during the operation of the centrifuge described above, a source of 
reduced pressure is activated which is effective through suction fitting 
74, suction duct 73 and suction space 72, reduced pressure is created in 
the interior of the centrifuge drum and, of course, also in the interior 
of collecting tank 36, which reduced pressure can, because of the sealing 
effect of separating flange 80 which dips into liquid layer 81, not be 
effective in the spaces of the device which are located above separating 
flange 80. The reduced pressure makes it possible, through connecting 
fitting 79 and intake duct 76, to suck from the mouth of the dentist's 
patient the mixture of liquids, solids and gases which is to be separated. 
In ring-shaped space 75 the mixture is taken up by the acceleration vanes 
33a. As a result of the centrifugal force which is effective there the 
gaseous phase is separated from the other two phases, with the gas flowing 
downwards inside the ring-shaped space along the outer surface of suction 
tube 70, while the solids and the liquid move outwards to the inside wall 
of separating tube 71 and there flow downwards under the influence of 
gravity. This process can be further improved by an acceleration of the 
flow which is obtained by designing ring-shaped space 75 in such a manner 
that it continually gets smaller in the downward direction, which can be 
ensured by appropriate conical design of suction tube 70 and/or separating 
tube 71 or of the wall surfaces of these pipes which form the limits of 
ring-shaped space 75 (not shown). 
After having been deflected by 180.degree. at the end of ring-shaped space 
75 along the bottom face of suction tube 70, the separated gas flows 
upwards through suction space 72 and is discharged through suction duct 73 
and suction fitting 74. Because of the cyclone effect at this point, drops 
of liquid which are being carried along by the gas are separated where the 
gas flow is deflected and carried outwards in the direction of wall 71 of 
the separating tube. FIG. 15 shows that the suction tube 70 ends at a 
distance from separating flange 80. 
The liquid/solids mixture remaining after the gas has been separated flows 
outwards along separating flange 80 and arrives in liquid layer 81 in 
which, because of the centrifugal effect, the solids are separated in the 
direction toward the peripheral wall 27 of the drum. The cleaned liquid 
flows upwards past the peripheral surface of separating flange 80, flows 
over barrier flange 30 which protrudes in a weir-like manner, and is 
discharged through overflow opening 31. 
When the centrifuge is shut off, the ring of water disappears and pressure 
equalization takes place above separating flange 80. The solids deposited 
at the peripheral wall 27 of the drum slide downwards along the peripheral 
wall of the drum as a result of gravity, continue sliding on the conical 
interior surface of the drum bottom 28 and pass through orifice 29 into 
collecting tank 36, as has been described above. The solids that have 
moved into collecting tank 36 and the water moving into collecting tank 36 
form, while the centrifuge is in operation, two separate layers on the 
outer wall of collecting tank 36, with the solids, because of the action 
of the centrifugal force and their greater density, being deposited on the 
wall of collecting tank 36, while a ring of water builds up in the inward 
direction toward the center of rotation, which can increase in thickness 
until excess water can again flow to the centrifuge drum through orifice 
29. From there it follows the path, described above, through overflow 
opening 31 into the discharge space for clean water. The level indicator 
described above responds to the thickness of the solids layer deposited in 
collecting tank 36 and signals that collecting tank 36 must be replaced or 
emptied. 
The device shown in FIGS. 15 and 16 can be modified in accordance with FIG. 
21. Here the suction tube 70 is, in the area of intake duct 76, closely, 
i.e. with a small gap, surrounded by enveloping tube 82 which, at its 
exterior peripheral surface is rigidly connected with the acceleration 
vanes 33a and therefore participates in the rotation of the centrifuge. 
Enveloping tube 82 ends at the upper ends, without touching it, at a 
distance from the wall surface of the housing 10b which forms the limit of 
inlet duct 76 from above, and reaches with its lower end into ring-shaped 
space 75. 
In this design of the device the sucked-in liquid/gas/solids mixture does 
not, as it does in FIGS. 15, 16 and 18, make contact with the stationary, 
i.e. non-rotating, suction tube 70, but with enveloping tube 82 which 
rotates with the same speed as the centrifuge. As a result, the solids and 
also the liquid contained in the mixture are flung outwards, away from the 
axis of rotation, by separating tube 82. As a result these phases of the 
mixture can definitely not flow downwards along the exterior peripheral 
wall of the stationary suction tube 70, so that parts of these phases 
cannot be carried along into suction space 70 during the 180.degree. 
deflection which takes place at the lower face of suction tube 70.