Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a two-cylinder thicl; matter pump ha~ing
a piston storage accordin~ to the preamble of claim 1.
With its piston storage the inventive two-c~linder thick matter pump
compensates pressure and volume fluctuations in the feed pipe that arise
between the strokes of the cooperating feed c~linders. These fluctuations.
that disturb the uniformity factor of the feed, are, for constructional
reasons, larger in the case of mechanicall~ controlled feed cylinders, e.g.
feed c~linders whose pistons are driven with a crankshaft, than in the
case of hydraulicall~ driven feed pistons, which allow the piston s :;rokes
to be covered but cannot prevent pressure and volume fluctuations in the
f eed pipe, either, when the piston of the feeding c~linder is switched
over to the suction stroke and the piston of the feed c~-linder sucl;ing
out of the prefilling vessel of the pump is switched over to the pressure
stroke. In this switch-over phase the piston storage presses thici; matter
into the feed pipe, thereb~- at least partly compensating the pressure and
volume loss of the sw-itch-over phase.
The inventive two-cylinder thick matte:r pumps thus differ from pis-
ton pumps ~h hich aim to improve the uniformit~v factor of the thick mat-
ter feed with at least three or even more feed cylinders, because with
such pump constructions thick matter must be sucl;ed out of the prefilling
vessel with the second or additional feed c~linders, while with piston
storages the additional feed volume passes from the feed pipe into the
storage and from there back into the feed pipe during the switch-over
phase of the feed c~linders. Thick matter pumps having more than two
feed c~linders to compensate volume and pressure fluctuations in order to
increase the uniformity factor in the feed pipe can reduce the pressure
fluctuations at the e~pense of a simple mechanical construction and sim-
ple control means, with a considerable increase in technical effort. but
they cannGt avoid speed droops in the feed.
The invention relates in particular to thick matter pumps which feed
sludge. This may be turbid coal slime for acting upon furnaces with fossil
D ~
~,
fuels ! sewage sludge. mortar and plaster compounds or the like. but par-
ticularl~- media which tend to solidify in the rest phase of their feed and
thus ca~e on the walls of feed paths that at times conduct no feed
stream. Such media are above all hydraulically setting media and sludges
with pozzolanic properties. It is often important to feed such substances
at a high uniformity factor because pressure and volume fluctuations in
following installations. e.g. in furnaces, cause difficulties or lead to con-
siderable dynamic stresses, which is the case in particular wlth high lifts.
To compensate such fluctuations the invention employs a piston stor-
age. Piston storages generally use a cylinder built onto the feed pipe and
opening into it on one side while its other end is closed b~ a movable
piston. Such piston storages differ from bubble storages by their piston,
and from air domes by the fact that the pumping medium is closed off in
the storage by a firm but movable wall. Piston storages permit virtually
any feed pressures and can therefore be used together with pumps that
reach considerable lifts.
The invention starts with a known thick matter pump $hat works
with a piston storage. The storage piston works with its side facing awa~-
from the pumping medium on a pressure cushion consisting of a high-
pressure gas. During the pressure stroke of the feed cylinders the storage
cylinder fills up with pumping medium from the feed pipe, whereby the
storage piston compresses the gas cushion. AS soon as the pressure col-
lapses, or drops, in the feed pipe in the switch-over phase, the high-
pressure gas cushion urges the piston in the opposite direction and press-
es pumping medium out of the storage cylincler into the feed pipe. Such a
piston storage can in fact improve the uniformity fac$ors of thicl; matter
feed.
However, the disadvantage is that a complete evacuation of the stor-
age cylinder is not ensured. This has various causes! but the consequence
is that pumping medium tending to cake or harden prematurely impairs
the storage relatively quickly and eventually blocks it. This not onl;Y re-
duces the uniformity factor of the feed b~lt also results in disturbances in
the feed which are relatively difficult to eliminate.
The invention is based on the problem of improving the uniformity
factor of feed in a two-cylinder thicl~ matter pump having the general
construction described at the outset, said irnprovement functioning per-
fectly even with a pumping medium that tends to harden prematurely or
cake on parts of the feed pipe.
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2~ 33~3
This problem is solved according to the invention by the features of
clalm 1. Further features of the invention are the subject of the sub-
claims.
Since the storage piston is driven by a hydraulic working cylinder
accordin~ to the invention, one can dispense with a gas cushion that
loads the storage pis$on, replacing it by the storage driving piston di-
rectly connected therewitht whose forced control with the feed cylinders
of the thick matter pump ensures that the storage piston is returnsd in
the storage cylinder for the storage to be filled, in the pumping phase,
and presses the storage content in the opposite direction into the feed
pipe, in the switch-over phase. The limits of travel of the storage driving
piston are hydraulicall~r fixed and therefore also determine the limits of
travel of the storage piston. whose outer extreme position in the storaga
cvlinder is selected in such a way that the storage is completely evacuat-
ed. Since these limits of travel are forced in each switch-over phase, the
pumping medium contained in the storage can at no time solldify and
block the storage.
The hydraulic medium required for supplying energy to the storage
driving cylinder can come from the pressure generator of the thick mat-
ter pump whose feed cylinders are directly driven by hydraulic working
cylinders. This considerably simplifies the storage operation, which re-
quires no external source of pressure gas. The forced control of the stor-
age driving piston also eliminates the irregularities in the storage piston
position which come about in particular when the lifting times of the
îeed c~linders are variable, which is the case in many thick matter pumps
for regulating the delivery.
Claim 2 proposes an embodiment of the invention which ensures b~r
hydraulic means that the storage cylinder is briefly evacuated in accord-
ance with the duration of the switch-over phase, and also makes it pos-
sible to fill the storage cylinder in the pumping phase following the
switch-over phase in such a way that the pumping medium penetrating
into the storage cylinder does not cause a pressure drop in the feed pipe,
which is effected b~r accordingly prolonging the time of filling of the
storage up to a maximum time! that may correspond to the pumping phase
but is selectable in individual cases. One thus obtains a virtually complete
uniformity of the feed stream. The brief evacuation of the storage is ef-
fected with the aid of the high-pressure hydraulic working medium of the
storage drive, while the longer duration of the storage filling is effected
2~ 133~
,
by regulating the stream into the storage driving piston ring space! in
which the hydraulic pressure acts in the same direction as the pressure
of the pumping medium on the storage piston and returns the storage
driving piston. The storage piston return time can be regulated with the
features of claim ~.
The embodiment of the invention as in claim 4 permits control of the
hydraulic pressure on the piston side in the storage driving cylinder, and
thus a fixing of the evacuation time of the storage cylinder. The hydrau-
lic accumulator provided for this purpose also allows for compensation of
wrong amounts of the hydraulic working medium for the storage opera-
tion.
The above-described regulation of the filling time of the storage cyl-
inder is made possible hydraulically in a simple way with the features of
claim 5. The adjustment is performed by hand, which offers the advantage
that the thick matter pump can be adapted at any time to the conditions
of a specific case of application, in particular to changing preconditions
which may be created by the particular pumping medium.
Claim 6, however, offers the advantage that an automatic adjustment
of the flow control valve allows for the storage filling to be adapted to
changing evacuation times of the feed cylinders, which OCCUI' particularly
when the thick matter pump is adjusted to different deliveries.
The invention shall be e~plained in more detail in the following with
reference to an exemplary embodiment that is shown in the connection
diagrams, of which
Fig. 1 shows schematically, i.e. free from all details that are unnec-
essary for understanding the invention, the connection state during evac-
uation of the piston storage into the feed pipe during the switch-over
phase of the feed cylinders, and
Fig. 2 shows the connection state during the filling of the piston
storage out of the feed pipe in the pumping phase of the feed cylinders.
The connection to the hydraulic pressure generator of the hydrauli-
cally driven feed cylinders of the thick matter pump is shown at 1.
Switch signals are present at 2 for the limits of travel of the pistons in
the feed cylinders or in hydraulic driving cylinders of the thick matter
pump.
The feed cylinders of the thick matter pump (not shown) work alter-
natingly on a feed pipe 3, one of the feed cylinders sucking the thick
matter out of a prefilling vessel of the pump, while the other feed cylin-
.. . .. .. . .. . . .. . . . ..
3 ~ ~
-
der presses its previously sucl~ed in filling into feed pipe 3. Directl~Y fol-
lowing the port of the feed cylinders, e.g. on the upper side of a bifur-
cated pipe ~hat combines the feed of the two feed cylinders, a storage
cylinder 4 is flange-mounted at 6. The opposite end of storage cylinder 4
is flange-mounted on a working cylinder 7 whose working piston 8 drives
a storage piston 10 mounted on its piston rod 9 and closing storage cyl-
inder 4 against flange 6.
Two seat valves 12 and 14 control hydraulic storage driving cylinder
7 and are indicated within the dot-dash line at 11. Seat valves 12 and 14
are piloted by a 2l2 directional valve. Piston space 11' closed by the full
piston area of storage driving piston 7 is connected directly to a hydrau-
lic accumulator 17 by a line 16 bypassing 2/2 directional valve 15. Line 16
feeds the 2/2 directional valve via a branch 18. Line 19 to hydraulic ac-
cumulator 17 opens into line 16 before directional valve 15. Connection 20
to the line coming from the pressure generator is located before line 19.
The 2/2 directional valve is switched over with the aid of a hydraulic
control line 2''. The switch-over takes place against the pressure from a
line 24 which is relieved from the tank via a choker 23.
In the switch-over phase shown in Fig. 1. the ''/2 directional valve is
changed over via line 22, so that hydraulic working medium reaches seat
valve 12 via line 18 to block the hydra,llic connection to piston ring
space 11 ' of storage driving cylinder 7 closed off from the ring area of
storage driving piston 8. At the same time, seat valve 14 is relieved from
the tank on its back via lines 30, 31, so that it unblocks the path via
line 27 to tank 28. Bypassing the 2/2 directional valve, high-pressure hy-
draulic working medium thus passes from hydraulic accumulator 17 to pis-
ton side 15 of the storage driving piston, so that storage piston 10 press-
es the volume OI pumping medium contained in storage cylinder 4 into
feed pipe 3.
An on-off valve 3Z in storage driving cylinder 7, which is controlled
hydraulically by piston 8, controls the limit of travel of storage driving
piston 8 in cylinder 7. The switch point is selected in such a way that
the total volume of storage cylinder 4 is pressed into feed pipe 3. The
piston ring side of storage driving cylinder 7 is depressurized via line 27.
This makes it possible to transfer the storage content into feed pipe 3
while overcoming the feed pipe pressure.
As soon as working piston 8 has îully evacuated storage cylinder 4.
the switch signal of valve 32 Iriggered thereby switches over the 2/2
3 ~ Ç~
directional valve. In the following pumping phase (Fig. 2). in which seat
valve 14 is closed via the storage pressure and seat valve 12 is opened b,v
the storage pressure, the hydraulic working pressure is applied to both
sides of storage driving piston 8. The hydraulic working medium pressure
built up in ring space 25 acts in the same direction on storage driving
piston 8 in cylinder 7 as the feed pipe pressure on storage piston 10 in
storage cylinder 4. This moves storage driving piston 8 in the opposite
direction, pressing hydraulic working medium via line 16 bypassing 2/2
directional valve 15 into hydraulic accumulator 17, which is fed from hy-
draulic pressure generator 1. This allows storage cylinder 4 to be filled
with medium from feed pipe 3 for compensation in the following swi~ch-
over phase. Flow control valve 25 is used to adjust the return time of
storage piston 10 to make it correspond to the duration of the feed
stroke of the thick matter pump, in order to prevent a change in delivery
due to the filling of the storage.
The return time of working piston 8 for filling storage 4 can be ad-
justed by hand by adjusting flow control valve 25. However, this adjust-
ment can also be performed automatically in order to adapt the return
time of the storage piston to changing lifting times of the thick matter
pump
Instead of changing over the 2/2 directional valve hydraulically, one
can also do this electrically via limit switches.
