Note: Descriptions are shown in the official language in which they were submitted.
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The invention rel.ates to a device for pumping free-flowing
media, in particular abrasive fluids, slurries, solid
suspensions or the like using a displacement pump interposed
between two check valves in the delivery line, said pump
suctioning the pumping medium upon its suction stroke and
passing on said medium upon its pressure stroke, whereby
a separating cylinder with an axially free movable separating
piston therein is arranged between the delivery line and
the working side of the pump, at the one face whereof is
located the pumping medium and at the other face whereof
is located an operation medium admitted by the pump, said
piston having a somewhat smaller diameter than the
separating cylinder.
When pumping solid suspensions and abrasive fluids thers is
the risk of damage to those parts of the pump which come
into contact w.~th the pumping medium. For this reason
diaphragm pumps are primarily used instead of piston pumps
for such pumping media. These, too, are subject to a high
wear and tear, as the diaphlagm is under a great strain
during pumping operation. Similarly diaphragm pumps cannot
be used for p~mping high temperature fluids.
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A pumping device of the type initiall~ described is known
~printed German application 1 453 576 laid open (Auslegeschrift)
1 453 576 ), havlng a se~arating piston can freely move
with clearance within the separating cylinder and is not
sealed from the inner wall of the separating cylinder,
with the result that the pumped medium can flow pa~ the
separating piston during operation and into the operation
medium. In order to prevent larger quantities of pumping
medium from getting into the operation medium, there is
provided between separating cylinder and displacement
pump a long conduit and an auxiliary pump which constantly
pumps the operation medium into the conduit -- between
displacement pump and separating piston.
In the case of this known pumping device the pumping medium
penetrated into the operation medium is in fact kept away
from the displacement pump sufficiently reliably but it is
still necessary for the conduit at least between displacement
pump and separating cylinder to be composed of a material
which cannot be corroded by the pumping medium. Moreover
separating cylinders and separating pistons are subject to
high wear and tear when pumping solid substance suspensions,
since the pumping medium constantly flows between separating
piston and cylinder and solid particles may become firmly
lodged in the gap. Even if slurries are to be pumped ,
difficulties can occur, since these block up the gap between
separating piston and separating cylinder thus impeding
the free movability of the separating piston. Furthermore
the known pumping device only functions if the separating
piston has approximately the same density as the liquid to
be pumped.
The object of the invention is toprovide a very simple and
robust device for pumping free-flowing media of the type
initially described, whereby the pumping medium
does not penetrate into the operation medium and does not
impede the movement of the separating piston within the
separating cylinder.
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This problem is solved by the invention in that the
separating piston is spring loaded by at least one
spring element acting against the pressure direction
of the pump and is sealed around its circumference
against the pumping medium.
This arrangement has the advantage that no pumping medium can
penetrate into the operation medium and both during
pressure stroke as well as suction stroke a small amount
of operation medium flows past the separa~ing piston into
the pumping medium which flushes the annular gap and the
packing therein. This effect is produced due to the fact
that in addition to the pumping force a force to overcome
the spring pressure must be applied by the pump upon press-
ure stroke, thus producing a pressure differential in the
operation medium and the pumping medium, which allows the
operation medium to flow past the separating piston.
Upon suction stroke, however, the spring element lets the
separating piston advance enabling the operation medium to
pass via the annular gap between separating piston and
separating cylinder into the pumping medium.
The separating piston subdivides the separating cylinder
into two cylinder chambers, which with the separating
piston in its final positions have 2 smaller volume than
the operation ~nedium moved by the pump during pressure and
suction stroke. In doing so the working s~e of the pump
is expediently connected to a supply tank, which is closed
to the pump upon pressure stroke. In this way an increase
in the pressure of the operation medium is achieved at the
end of the pressure stroke, if the separating piston has
reached its extreme position. As a result of the pressure
differential between operation medium and pumping medium a
certain volume of the operation medium can flow past the
packing into the pumping medium and flush the packing and
peripheral edge of the separating piston free from pumping
means, thus ensuring a perfect sealing of the separating
piston at the separating cylinder, when the displacement
pump ~egins its suction stroke and the separat~ng piston
once again suctions pumping medium.
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~ this purpose the separating piston is provided with at least
one gasket haYlng a sealing lip continguous to the inner wall of
the cylinder and being directed towards the cylinder chamber
filled with pumping medium. This sealing lip is flushed and
cleaned by the operation medium flowing through the annular gap
between separating piston and inner wall of the separating cy-
linder. In neutral position the sealing lip then fits closely
to the inner wall of the separating cylinder so that no pumping
medium can flow back into the operation medium.
Betweer. the supply tank and the working side of the pump a
first non-return valve preloaded against the supply tank and
a second non-return valve preloaded against the working side of
the pump is respectively arranged and controlled by the sepa-
rating piston. By this construction the inlet from the supply
tank remains closed while the pump carries out its pressure
stroke and the second non-return valve is opened at the end
of the suction stroke of the separating piston; the first non-
return valve, however, only opens when there is a low pressure
on the working side of the displacement pump, which exceeds
the spring force closing the first non-return valve.
To control the second non-return valve the latter can have a tappet
which protudes into the separatin~ cylinder and is admitted
by the separating piston in the last phase of the suction
stroke. Hereby it is particularly expedient for the valve
bodies of the first and second non-return valves to be pressed
on their seats by a common valve spring~
On the front face of the separating piston facing the dis-
placement pump a spring can be arranged which retards the
action of the separating piston in its suction stroke and
softens the impact of the separating piston on the
separating cylinder casing.
For this purpose the separating cylinder has stops in both
cylinder chambers which reciprocally limit the stroke of
the separating piston and the one cylinder chamber of the
separating cylinder can be connected by one conduit to the
delivery line and the other cylinder chamber by one conduit ~
to the working side of the piston pump actLng as displacement
pu~.
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It is particularly expedient to adapt the si~e of the
flow inlet between separating cylinder and separating
piston to meet the volume of the operation medium which
is to be pressed into the pumping medium with each
pressure stroke. Such a construction ls then particularly
advantageous if a metered volume of a particular medium
is to be added to the pumping medium with every stroke
of the pump. In this case the operation medium is composed
of this additive which is topped up constantly from the
supply tank. If the pumping medium is a bauxite slurry,
for example, to which sodium hydroxide solution is to be
added during pump operation, then the supply tank can
contain the sodium hydroxide solution to be added to the
pumping medium. In other cases the supply tank contains a
flushing liquid or the operation medium, which can be
any suitable hydraulic fluid, for e.g. an oil or water,
which exerts no adverse effect on the pumping medlum if
added thereto in small quantities during the pump operation.
Further features and advantages of the invention will be
apparent from the following description, in which a preferred
embodiment of the invention is more closely illustrated by
means of an example. It shows :
Fig. 1 a pumping device according to the
invention in a schematic sectional
view and
Fig. 2 ltem II of Fig. 1 on an enlarged
scale, showing the packing or sealing
of the separating piston at the
separating cylinder.
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The drawings show a pumping device 10 for the pumping
of free-flowing media, in particular an abrasive fluld
such as e.g. a bauxite slurry which is hereinafter
abbreviated as " pumping medium " and identified in the
drawing as 1 1 . The pumping medium flows in the direction
of arrow 12 in a pump hose 13, in which two bypass valves
14 and 15 are located, said valves being ball valves, and
are housed in a valve casing 16. Between the two bypass
valves 14 and 15 ~here is a pipe joint socket 17 to which
a conduit 18 is connected, leading to a separating cylinder,
marked collectively as 19.
In the separating cylinder 19 there is a separating
piston 20 freely displaceable in axial direction, which
subdivides the separating cylinder 19 into a lower cylinder
chamber 19a and an upper cylinder chamber 19b. The conduit
18 already mentioned is connected to the lower cylinder
chamber 19a, which leads to the valve casing 16 ofthe pump
hose 13. A conduit 21, filled with an operation medium 40,
connected to the working side 22, a displacement pump 23,
which is a piston pump in the embodiment example illustrated
enters into the upper cylinder chamber 19b. The pump housing
is marked 24 and the pump piston bears the reference number
25. The piston rod 26, only schematically indicated here,
acts upon the piston 25, which is moved by the crankshaft 27
and imparts a reciprocal movement to the piston 25.
As seen from Fig. 1 the separating piston 20 has a peripheral
edge 28 enlarged in axial direction, which protrudes beyond
the lower face 29 of the separating piston and touches the
one face 30 of the separating cylinder upon pressure stroke.
On the opposite face 39 of the separating piston a protuber-
ance 31 is fitted which can touch the upper face 32 of the
separating cylinder and hereby limit the suction stroke
of the separating cylinder.
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From Fig. 2 it is evident that the separating piston 20
has a diameter d which is somewhat smaller than the
diameter D of the separating cylinder, leaving as a result
an annular gap 33 between the separating cylinder 19 and
the separating piston 20. This annular gap is sealed by
two lip seals 34 arranged consecutively in axial direction
which are each located respectively in a peripheral
groove 35 of the separating piston and have a sealing lip
37 contiguous to the inner wall of the cylinder 36, said
lip being directed at the cylinder chamber 19a filled with
pumping medium 11. The annular groove has a quite definite
dimension which is explained in more detail further below.
In the upper ront cover38 of the separating cylinder 19
there is a bore 41 through which the tappet 42 of a disk
valve 43 protrudes into the upper cylinder chambe~ 19b of
the separating cylinder. The disk valve 43 is located
together with a ball return valve 44 in a valve casing 45,
which is fixed to the upper front cover 38 of the separating
cylinder 19 and belongs to a hose 46 which leads to a supply
tank 47, in which the operation medium or a special flushing
liquid 48 is located.
As seen from Fig. 1 the spherical closure of the non-return
valve 44 and the valve disk of the disk valve 43 are pressed
against their seats by a valve spring 49 common to both and
kept closed. The disk valve 43 is raised from its seat, if
the annular enlargement 28 of the separating piston 20
pushes against the end of the valve tappet 42 protruding into
the cylinder chamber 19b and displaces this in axial
direction, if the separating piston 20 in Fig. 1 moves
upwards.
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When the displacement pump 23 is not operable
the separating piston 20 is held approximately in
the middle of the separating cylinder 19 by two
springs 50 and 51, said spring 50 being located in the
lower cylinder chamber 19a and said spring 51 being
located in the upper cylinder chamber 19b of the
separating cylinder 19.
The mode of operation of the device is as follows :
If the piston 25 of the displacement pump 23 is moved in
a downwards direction by the connecting rod 26 in Fig. 1
and ii said piston carries out its pressure stroke, the
operation medium 40 located within the conduit 21 presses
on the upper face 39 of the separating piston with the
result that the former likewise is pressed downwards in
Fig. 1 and exerts a pressure on the pumping medium 11
located in the conduit 18 and in the valve casing 16. With
this increase in pressure the non return valve 15 in the
valve casing 16 is kept closed, whereas the non return
valve 14 opens and the pumping medium is passed along in
the direction of the arrow 12 within the delivery line 13.
As the separating piston 20 i5 under the action of spring
50, the liquid pressure produced in the conduit 21 by
piston 25 of the displacement pump must be greater than
the pressure for pumping the pumping medium within the
conduit 18 and the delivery line 13, if the separating
piston 20 in the separating cylinder 19 is pressed down-
wards. As a result of the pressure differential in the
conduits 21 and 18 the operation medium 40 flows through
the annular gap 33 between separating piston 20 and
separating cylinder 19 past the sealing lips 37 into
the pumping medium, and in doing so flushes the seals 34.
The same effect also occurs if the separating piston 20
contacts the face 30 of the separating cylinder 19, before
the piston 25 of the displacement pump 23 reaches its
bottom dead centre, if the cylinder chambers 19a and 19b
in the final positions of the separating piston 20 have a
smaller volume than the operation medium displaced by thP
pump 23 upon pressure and suctlon stro~e.
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When the piston 25 has reached its bottom dead centre
and the piston pump 23 begins its suction stroke, the
separa~ing piston 20 is carried upwards by the low
pressure arising in the conduit 21, whtch for its part~
produces a low pressure in the conduit 13 and in the
valve casing 16, whereby the non-return valve 14 is closed
and the non-return valve 15 in the delivery line 13 opened
and pumping medium suctioned out of the delivery line 13.
sefore the separating piston 20 comes to rest at the
upper face 32 of the separating cylinder 19, the outer
annular enlargement 28 on the separating piston 20 pushes
against the tappet 42 of the disk valve 43 and lifts this
from its seat. As the separating piston 20 is retarded in
its up stroke by the spring 51, but the piston 25 of the
displacement pump 23 however continues its suction stroke
after the separating piston 20 has contacted the upper face
32 of the separating cylinder 19 , a low pressure occurs
in the conduit 21. As the sealing lips 37 of the lip seals
34 are directed to the lower cylinder chamber 19a filled
with pumping medium 11, said sealing lips 37 are pressed
by the pumping medium 11 firmly against the inner wall 36
of the separating c~linder. Due to the simultaneously
effective lower pressure in the interior of the valve casing
45 the non-return valve 44 is lifted from its seat, with the
result that the fluid 4~ in the supply tank 47 can flow
through the valve casing 45 into the cylinder chamber 19b
and supplement the operation medium 40, while the piston
25 of displacement pump 23 continues its suction stroke.
The cylinder chamber 19b and the conduit 21 are then once
again completely filled with fluid, when the piston 25
reaches its upper dead centre.
It is evident that the pumping device according to the
invention can be used simultaneously as a metering device,
with which a fluid 48 present in the s~pply tank 47 can
be added in metered quantity to the pumping medium 11,
whereby the force of the spring 50, the cylinder chambers
19a and 19b and the width of the annular gap 33 can be
attuned to one another in such a way that with every suction
stroke a quite definite quantity of fluid 4~ passes into
the conduit 21 and is pressed past the lip seals 34 into
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the pumping rnedium 11 upon pressure stroke. In this
way the fluid additive 48 can be the same fluid as the
operation medium 40. It is, however, also possible to
use a fluid additive which is different from the
operation fluid, as when using the injection inlet
arrangement for the fluid additive in the upper face 38
of the separating cylinder 19 as shown, - an arrangement
not insignificant to the invention - there is hardly any
mixing of the operation fluid in conduit 21 and the fluid
additive injected into the upper cylinder chamber ~9b.
The invention can be used in industry for the pumping of
free-flowing substances, in particular aggressive and
abrasive slurries such as bauxite suspensions or carbon
slurries. As operation medium a hydraulic fluid e.g. a
mineral oil, but also water, sodium hydroxide solution
or another additional fluid can be used, which is to be
injected into the pumping medium and can be supplemented
or refllled from the additional tanks 48.
The invention is not restricted to the embodiment example.
It is also possible, e.g. to use even differently formed
and differently controlled valves for the injection of
the fluid additive, without hereby exceeding the scope
of the invention.
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