Note: Descriptions are shown in the official language in which they were submitted.
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WO 99/29166 1 PCT/N098/00371
A dosing device and a method for dosed feeding of
grained, palletized or granulated mass material out
.from a c:~mtdimer.
The invention relates to a dosing device for feeding out
doses of grained, palletized or granulated material from a
container, particularly for feeding out palletized fish fod-
der from a silo.
Grained, palletized or granulated material, in the following
called pellets, is often stored in a silo, from where feed
out occurs close to the bottom, while filing of new material
is effected from the top of the silo. An advantage with this
1o is that the oldest material substantially is located lower-
most in the silo and becomes fed out first. The arrangement
also makes it possible to utilize the gravity in an advanta-
geous way in order to achieve controlled feed out of pellets
by means of a dosing device.
A simple known dosing device comprises a flap or a hatch
capable of opening and closing an outlet aperture lowermost
in the silo. When the hatch is opened, pellets flow out from
the silo, down into a vessel or down onto a conveyer belt be-
low the silo. When the desired amount of pellets has been
drawn off, the hatch closes the outlet aperture. The amount
can often be determined with sufficient accuracy by control-
ling the opening time of the hatch by means of a timing de-
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vice. Better accuracy can be achieved by means of a control-
ler receiving signals from a weight or volumetric measuring
accessory, the signal value being compared to a predetermined
value.
s In some cases, a silo may be placed straight above the place
where the dosed material is used. Examples of this technique
are silos associated with simple mixing plants and silo-
shaped automatic fodder containers somewhat spaced above the
water surface in fish vessels or fish "mends".
1o Very often, the dosed material is to be used at a place
spaced from the silo, and the dosing device is then combined
with a conveyor, e.g. a conveying belt such as previously
mentioned.
A much used dosing device comprises a conveying screw within
1s a channel, where the outlet aperture of the silo opens
straight into the channel, without any intermediate flap or
hatch. When the conveying screw is not rotating, it effi-
ciently prevent material from flowing out from the silo.
A rotary sluice is another dosing device very much used,
2o comprising a shovel bringing pellets from the outlet aperture
of the silo to a pipe where flowing air or liquid conveys
dosed material further on.
Conveyor screws and rotary sluices are simple and robust.
Additionally, they can easily be adapted to give volumetric
2s measure of dosed amount by counting revolutions. Moreover,
the rotational speed of the conveyor screw and of the shovel
may easily be changed in order to achieve desired volume
rate.
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In order to enable to empty a pellet silo completely, it is
usual that the lowermost portion of the silo is shaped as a
funnel.
Anyone versed in the art is aware of that pellet bridges may
s form if the funnel angle is too large. A pellet bridge re-
sults in that only pellets beneath the bridge reach the out-
let aperture of the silo. A small funnel angle results in
that the funnel becomes relatively high and in that the fun-
nel volume is small.
io Also, it is known to be advantageous to couple the outlet ap-
erture of the silo to an expansion chamber having a larger
lateral measure than the outlet aperture of the silo, so that
the pellet mass is allowed to expand after having passed
through the outlet aperture. Thus, a much used silo type
is opens out within a ball-shaped chamber having a substantially
larger diameter than the outlet aperture of the silo. The
diameter of the expansion chamber is also significantly
larger than the diameter of a conveyor screw extending
through the expansion chamber. By using a rotary sluice, the
2o pellet material is allowed to expand in the shovel.
Pellet bridges occur even with a small funnel angle and ex-
pansion chamber. It is, thus, usual to provide the expansion
chamber, the sluice housing or the silo wall with an inspec-
tion hatch where it is possible to reach a pellet bridge with
25 a tool to loosen up the bridge.
A silo for pellets becomes relatively tall. First, as men-
tioned, it is necessary with a tall funnel and, secondly, it
is an advantage to have an expansion chamber in connection
with a dosing device below the outlet aperture, and these
3o measures contribute to increase the silo height. Tall silos
are, generally, a disadvantage, and a resultant point of
gravity at a high level is particularly a disadvantage on
board floating installations.
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Silos are often placed such that it is difficult to reach the
area below the silo in order to maintain the dosing device or
to loosen up a pellet bridge through an inspection hatch.
Technical installations beneath or immediately adjacent a
s silo also makes it difficult to pass a conveyor screw or con-
veying belt for pellets out from the silo.
Another case is that there might be a need for a plurality of
outlets from one silo. It is known to have several hatches or
flaps side by side and, correspondingly, several conveyor
io belts in order to convey pellets to a plurality of places of
use. Also, solutions comprising two silos having a common ex-
pansion chamber are known. Several outlets become often both
space-demanding and impractical.
The object of the invention is to provide a method in dosing
is and a dosing device where said disadvantages have been
avoided.
The object is achieved through features as defined in the
following specification and claims.
According to the invention, pellets are sucked out from the
2o silo by means of a flow of air within a pipe connected to the
suction side of one or another low-pressure source, and where
the free end of the pipe is passed into the silo and into the
pellet mass. The pipe may be assigned a sluice device, a cy-
clone or another apparatus adapted to receive pellets accom-
2s panying the air flow. Negative pressure within the pipe draw
air from the area above the pellet mass, through the pellet
mass and into the pipe at the open, lower end thereof. Pel-
lets close to the end of the pipe, are entrained into the
pipe and further upwardly within the pipe by means of the
3o flow of air.
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A controlled valve can open and close at least one gate in
the pipe wall. When the gate is closed, air flows into the
pipe at the free end thereof, such as mentioned. When the
valve is open, air flows into the pipe through the gate. Pel-
lets within the pipe, downstream of the gate, is conveyed
further by means of air entering into the pipe through the
gate.
Supply of new pellets at the open end of the pipe stops, be-
cause the air speed there is too small to entrain pellets
io when the gate is open. Thus, pellets may be dosed into the
pipe through changing the valve between closed and open posi-
tion.
The invention can be embodied in several ways. It should be
made provisions preventing pellets from accompanying air
flowing through the valve, so that pellets do not enter the
pipe or clogs the valve. This may be achieved in a simple
manner by shielding the valve, e.g. with a net having so
small meshes that pellets can not pass.
Further, it may be advantageous to dispose a movable arm ad-
2o jacent the open end of the pipe. The movements of the arm
loosens up a possible local pellet bridge preventing flow of
pellets therethrough.
In the following, an exemplary embodiment of the invention is
discloses; reference is made to the attached drawings,
wherein:
Figure 1 shows diagrammatically in side elevational view a
silo having a dosing device;
Figure 2 shows the dosing device, on a larger scale, in sec-
tion in side view, the dosing device occupying an operative
3o condition;
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Figure 3 shows the dosing device, on a larger scale, in sec-
tion in side view, the dosing device occupying an inoperative
condition.
In figure 1, reference numeral 1 defines a dosing device
placed within a silo 2 containing pellets 3.
By means of a conveying hose 4, the dosing device 1 is cou-
pled to the suction side of a fan 5, possibly a compressor,
an ejector or another apparatus suitable to create a negative
pressure within the conveying hose 4.
1o Further, the dosing device 1 is connected to a pressure air
source 6 by means of a pressure air pipeline 7 through a con-
trolled valve 8. A controller 9 is connected to the con-
trolled valve 8 and adapted to give it signals to open or to
close.
is The dosing device 1 which in figure 2 is shown in operative,
vertical position of use, comprises a central pipe 10 coupled
to the conveying hose 4 and constitutes an extension thereof.
In the wall of the pipe 10 is formed some holes 11, admitting
flows of air into the pipe 10. An axially displaceable sleeve
20 12 surrounding the pipe 10, is provided with holes 13 posi-
tioned in a similar pattern as the holes 11 in the pipe 10,
so that the holes 13 in the sleeve 12 can be brought to over-
lap the holes 11 in the pipe 10 by displacing the sleeve 12
along the pipe l0.
2s When the sleeve 12 occupies a first operative end position,
such as shown in figure 2, the holes 13 do not overlap the
holes 11. Then, negative pressure within the hose 4 and pipe
10, results in that air and pellets flow into the pipe 10 at
the open end thereof.
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When the sleeve 12 occupies another, inoperative end posi-
tion, such as shown in figure 3, the holes 13 overlap the
holes 11. Then, negative pressure within the hose 4 and pipe
results in that air flowing into the pipe through the
s holes 13,11. Air flowing into the pipe 10 at the open end
thereof, attains then a too small speed in order to draw pel-
lets 3 into the pipe 10.
A perforated screen 14 surrounds a substantial portion of the
pipe 10 and prevents that surrounding pellets 3 come into
1o contact with the sleeve 12, the screen 14 extending between a
first flange 15 and a second flange 16 attached to the pipe
10. The distance between the flanges 15, 16 is such that the
flanges 15, 16 may serve as end stops for the sleeve 12. The
screen 14 is made of net or perforated material having so
small openings that pellets 3 cannot pass therethrough.
At its outer periphery, an annular diaphragm 17 is pressure-
sealingly attached to the first flange 15, at that side fac-
ing the second flange 16, by means of a ring 18 and screws,
not shown. Further, the diaphragm 17 is pressure-sealingly
2o attached to the sleeve 12 between a first disc 19 and a sec'
and disc 20 by means of screws, not shown, the second disc 20
being pressure-sealingly attached to the sleeve 12.
By means of a nipple 21, the pressurized air pipeline 7 is
connected to a gate 22 in first flange 15, so that pressur-
ized air can be supplied between first flange 15 and the dia-
phragm 17.
A pretensioned spring 23 acting between second flange 16 and
second disc 20, keeps the sleeve 12 in first end position,
see figure 2. The sleeve 12 can be displaced against the
3o force from the spring 23 to second end position, figure 3,
through the supply of pressurized air between first flange 15
and the diaphragm 17.
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Upon periodically supply of pressurized air, the sleeve 12
can be brought to alternate between first and second end po-
sition.
A strut 24 extending parallell to the pipe 10 is, at one end
s thereof, attached to second disc 20 and penetrates second
flange 16.
Thus, the strut 24 follows the movements of the sleeve 12.
Onto the free end of the strut 24 is fastened an arm 25 sub-
stantially extending laterally of the pipe 10 at a distance
1o from the free end of the pipe 10. The movements of the arm 25
loosen up a possible pellet bridge which may prevent supply
of pellets at the free end of the pipe 10.
Also, the sleeve 12 could of course have been adapted such
that it turns between two end positions, the sleeve 12 in one
1s end position closing the holes 11 in the pipe 10 and opening
the holes 11 in the pipe 10 in the other end position.
Upon a need for several outlets from a silo 2, a plurality of
dosing devices 1 are installed within the silo 2.
