Note: Descriptions are shown in the official language in which they were submitted.
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PUMPING SYSTEM
BACKGROUND OF THE INVENTION
[0001] This invention relates to a pumping system and to a pressure vessel
assembly
for use, particularly, in a slurry pumping system.
[0002] The efficient pumping of slurry is technically challenging. Typically
use is made
of centrifugal pumps connected in series to achieve target pumping pressures.
For
example to operate at a pressure of about 20 bar seven pumps, each capable of
achieving about 3 bar pressure, are required.
[0003] Slurry can be highly abrasive. Thus the wear parts of the pumps must be
lined
with abrasive-resistive materials. Clearances in the pumps must be generous to
minimise wear and this adversely impacts on the efficiency of the pumps. A
further
negative factor is that the impeller speed in a centrifugal slurry pump must
be low to
avoid excessive erosion of the impeller and volute casing.
[0004] Sacrifices which are made to pumping efficiency in order to obtain
increased
pump life translate into higher energy consumption. Even then maintenance
costs are
high due to the frequent replacement of wear parts.
[0005] Various techniques have been proposed in the prior art to address the
aforementioned aspects. Reference is made in this regard to the following
documents:
US4,229,143, UK945624, US5213478, EP0249655, W097/49897, US3951572,
US2002/0011579 and W02006/076827.
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[0006] Without exhaustively examining these documents it should be noted that
in
some cases use is made of mechanical connections between drive and driven
components, an approach which can add significantly to technical problems. If
an oil-
based hydraulic fluid is used to transfer energy a potentially damaging
environmental
problem is created. Some techniques which are capable of pumping a low volume
of
slurry at a high pressure cannot, practically, be extended to operate at high
pump rates
e.g. in excess of 450 cubic metres per hour, and at high pressures.
[0007] A need exists for a system which is capable of pumping slurry in an
efficient
manner and at a substantial rate which can be sustained without unacceptable
fluctuations in the flow rate and wherein the effects of wear and abrasion are
addressed, and wherein the use of glands is reduced, if not eliminated.
[0006] An object of the invention is to provide a slurry pumping system which,
at least
partly, addresses one or more of the aforementioned requirements.
SUMMARY OF THE INVENTION
[0009] The invention provides in the first instance a pressure vessel assembly
which is
suited for use in a pumping system which includes:
(a) an elongate cylindrical pressure vessel with a longitudinal axis, an upper
substantially hemispherical end with a first fluid port, and a lower
substantially
hemispherical end with a second fluid port,
(b) an elongate flexible bladder, inside the pressure vessel, which has a
substantially hemispherical lower end and a mouth, at an upper end which, on
an outer
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side, is sealingly engaged with the pressure vessel, the bladder defining a
second fluid
volume of variable size between an outer surface of the bladder and an inner
surface of
the pressure vessel, and
(c) an elongate valve tube which extends inside the bladder along the
longitudinal
axis, and which has a plurality of flow apertures at respective locations
along its length,
an upper end, through which is formed a flow passage and which is located
within and,
externally, is in sealing engagement with, the mouth of the bladder, and a
lower end.
[0010] Preferably the pressure valve assembly includes a sensor for detecting
elongation of the bladder, inside the pressure vessel, beyond a predetermined
position.
[0011] The sensor may be of any suitable type but preferably includes an
elongate
member, inside the valve tube, with a lower end which projects from the valve
tube and
which is fixed to the lower end of the bladder and a switch which is actuable
upon
unwanted movement of the elongate member, e.g. movement of an upper end of the
member away from a predetermined location.
[0012] The valve tube may have a plurality of longitudinally extending sides
which,
optionally, may nominally be flat, and each side may have a number of flow
apertures.
Preferably each flow aperture is bounded by a respective arcuate surface which
extends towards an interior of the valve tube. This feature is intended to
reduce the
likelihood that the bladder can be damaged by edges of the valve tube
particularly in the
region of each flow aperture.
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[0013] Preferably the total cross-sectional area of the flow apertures, per
unit length of
the valve tube, increases from the upper end of the valve tube towards the
lower end of
the valve tube.
[0014] The valve tube and the bladder may be configured so that, upon
collapse, the
bladder has an elongate central core which abuts the valve tube, and a
plurality of
elongate pleats which extend radially from the core and which are angularly
displaced
from one another in a circumferential direction around the core, and wherein
each pleat
is respectively formed by first and second elongate sections of the bladder
with opposed
surfaces in contact with each other.
[0015] The first fluid port may be a port for a driving fluid, e.g. water,
i.e. a fluid which
delivers energy to the assembly. The second fluid port may be a port for a
driven fluid,
e.g. slurry, i.e. a fluid which draws energy from the assembly.
[0016] The invention also provides a bladder for use in the pressure vessel
assembly
which includes an elongate cylindrical body which is made from an elastically
deformable material with a substantially hemispherical lower end, a
substantially
hemispherical upper end, and a tubular mouth at the upper end which includes a
circumferentially extending seal formation.
[0017] This seal formation may be in the nature of an O-ring which is
integrally formed
with the remainder of the body. Any suitable material may be used for making
the
bladder, e.g. rubber, a synthetic rubber-like material (elastomeric) or the
like. The
invention is not restricted in this regard.
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[0018] The invention further extends to a pumping system which includes first
and
second pressure vessel assemblies, each assembly being of the aforementioned
kind, a
first fluid manifold connected to the first fluid ports of the pressure
vessels, a pump for
pumping a first fluid to the first fluid manifold, a second fluid manifold
connected to the
5 second fluid ports of the pressure vessels, and a controller which regulates
operation at
least of the first fluid manifold so that, during a pumping cycle, the second
fluid flows
through the second fluid manifold into the second fluid volume of the first
pressure
vessel assembly at least while the pump pumps the first fluid into the bladder
of the
second pressure vessel assembly thereby to expand the bladder and displace the
second fluid from the associated second fluid volume, through the second fluid
manifold, into a pipeline.
[0019] In one particular application the first fluid is water, and the second
fluid is slurry.
[0020] The controller may be operated continuously so that the slurry volumes
of the
pressure vessels are alternately filled with slurry and so that water is
pumped into the
bladders of the pressure vessels alternately thereby to expel slurry from the
respective
slurry volumes, to deliver a continuous flow of slurry.
[0021] Preferably use is made of a damper which contains a gas, for example
air, at a
pressure which is dependent on the level of slurry in a slurry feed tank.
[0022] In use of the pumping system slurry is caused to flow into the slurry
volume of a
pressure vessel. The bladder of the pressure vessel is thereby caused to
collapse from
its lower end towards its upper end. As the bladder collapses onto the valve
tube,
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inside the bladder, the flow apertures in the valve tube are closed
successively from the
lower end to the upper end of the valve tube. Consequently the flow rate
through the
valve tube is progressively decreased and is reduced to zero when the bladder
is fully
collapsed. This process serves to dissipate the momentum (kinetic energy) in
the
incoming slurry flow to the pressure vessel, thereby eliminating any fluid
hammer in the
incoming slurry feed line when the slurry volume is full.
[0023] In order to achieve a smooth slurry flow from the system, i.e. to avoid
slurry flow
rate fluctuations when diverting water flow from one bladder to the other, the
pump is
also used to pressurise the bladder of one pressure vessel assembly prior to
the end of
a pumping cycle based on the use of the bladder in the other pressure vessel
assembly.
[0024] The control valves, in the system, function concomitantly to divert
water flow
progressively from one bladder to the other thereby to eliminate pressure
spikes in the
water system and therefore also in the slurry system. This pressure
equalization is
achieved by means of a pilot valve which supplies a small quantity of water to
the target
bladder. After start-up of the pumping system the water pump thus operates
continuously and delivers a constant flow rate which can however be adjusted
as
necessary to take account of the slurry supply rate.
[0025] As the vessels are pre-pressurized, or de-pressurized, as the case may
be,
before any valves are actuated the pressure differential across the valves is
effectively
zero. This factor materially extends the operating lifetime of the valves,
particularly so
when highly abrasive slurries are being pumped.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention is further described by way of example with reference to
the
accompanying drawings in which:
Figure 1 is a side view in section of a pressure vessel assembly according to
the
invention,
Figure 2 shows, on an enlarged scale, a sensing arrangement used to prevent
damage
to a bladder of the pressure vessel assembly arising due to excessive
deformation of
the bladder,
Figure 3 is a side view in cross section on an enlarged scale of an upper end
of the
pressure vessel included in the assembly of Figure 1,
Figure 4 is a cross-sectional view in plan of a valve tube included in the
assembly of the
invention,
Figure 5 is a perspective view of a bladder which is used in the assembly of
Figure 1,
Figure 6 shows the bladder when it is fully collapsed around the valve tube of
Figure 4,
Figure 7 is a view in cross section and in plan of a pressure vessel with an
internal
bladder in a relaxed state,
Figure 8 is similar to Figure 7 but showing the bladder fully collapsed, and
Figure 9 is a schematic representation of a slurry pumping system based on the
use of
two pressure vessel assemblies, each of the kind shown in Figure 1.
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DESCRIPTION OF PREFERRED EMBODIMENT
[0027] The invention is described hereinafter with particular reference to the
use of
water to pump slurry. This however is exemplary only and non-limiting, for
other
applications of the pressure vessel assembly, and of the pumping system,
exist.
[0028] Figure 1 of the accompanying drawings is a side view in cross section
of a
pressure vessel assembly 10 according to the invention.
[0029] The assembly includes an elongate, cylindrical pressure vessel 12 which
is
made from suitable steel with a lower, substantially hemispherical end 14 and
an upper,
substantially hemispherical end 16.
[0030] A port 18 is positioned at the lower end 14 centred on a longitudinal
axis 20 of
the vessel. A port 22, also centred on the longitudinal axis, is positioned at
the upper
end 16. In this application the port 18 is for a driven fluid i.e. slurry
which is pressurised
in the vessel. The port 22 is for a driving fluid i.e. water under pressure
which inputs
energy for the assembly.
[0031] The slurry port 18 is connected via a suitable coupling 24 to a slurry
manifold 26
which is described in greater detail hereinafter with particular reference to
Figure 9. The
water port 22 is connected via a suitable connector 28 to a water manifold 30
which is
also described hereinafter in greater detail with particular reference to
Figure 9.
[0032] An elongate valve tube 34, which is shown in cross section in Figures 7
and 8
and on an enlarged scale in Figure 4, extends downwardly inside the pressure
vessel
12. In this example of the invention the valve tube has six sides 38 which are
nominally
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flat. Adjacent sides adjoin at junctions 40 which lie on a circumference 42 of
a circle. A
plurality of flow apertures 46 are formed in the respective sides. Each flow
aperture is
bounded by a respective arcuate surface 48 which extends towards an interior
of the
valve tube. This feature is intended to reduce the likelihood that the bladder
can be
damaged in the region of each flow aperture, particularly by edges 50 of the
valve tube.
[0033] Referring to Figure 1 it is evident that the apertures are centrally
positioned in
the respective sides and are closer to each other at a lower end 52 of the
valve tube.
The spacing 54 between adjacent flow apertures increases towards an upper end
56 of
the valve tube. In addition, particularly near the upper end 56, the sizes of
the apertures
are significantly reduced. Due to the variations in aperture sizes, and
spacing, the total
area of the flow apertures, per unit length of the valve tube, decreases
towards the
upper end of the valve tube.
[0034] A bladder 60 is positioned inside the pressure vessel and the valve
tube is
located inside the bladder. The bladder has an elongate body 62 which, as
shown in
Figures 5 and 7, is generally cylindrical and has a substantially
hemispherical lower end
64 and a substantially hemispherical upper end 66. The bladder is made from
any
appropriate material e.g. rubber or any equivalent synthetic material known in
the art.
The invention is not limited in this regard.
[0035] Figure 3 illustrates on an enlarged scale and in cross section a
portion of the
upper end 66 of the bladder. This end is formed with a tubular mouth 68 which
flares
outwardly slightly and which terminates in a sealing formation 70, in the
nature of an 0-
ring seal, which is integral with the tubular mouth. The tubular mouth is
positioned
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inside a tapered bore 72 of the pressure vessel with the O-ring formation 70
in a
complementary recess 74. A tapered flange 76 which, itself, is externally
sealed by
means of an O-ring 78, is used to secure the tubular mouth to the tapered
bore. An
upper end of the tapered flange extends to the connector 28 shown in Figure 1.
An air
5 vent valve 80 is operable to bleed air from a volume (referred to
hereinafter as a slurry
volume 192) between an inner surface of the pressure vessel 12 and an outer
surface
of the bladder 60 - see Figures 1 and 9.
[0036] The circumference 42, referred to in connection with Figure 4, is
marked in
Figure 3. This constitutes an upper end of the valve tube 34 which extends
downwardly
10 inside the bladder and which is centred on the longitudinal axis 20 of the
pressure
vessel.
[0037] Figure 2 illustrates additional constructional details of a sensing and
switch
mechanism 82 at the upper end of the bladder and at the lower end. An elongate
member 84, e.g. a corrosion-resistant rod, e.g. of stainless steel, extends
through the
valve tube 34. An upper end 86 of the rod carries a switch bobbin 88 which is
secured
to the rod by means of a grub screw 90. A proximity switch 92 fixed to an
appropriate
housing 94 is used to detect movement of the bobbin. At a lower end the
housing 94 is
attached to a spigot 96 which projects outwardly from part of the connector
28. The
housing is fixed to the spigot by means of one or more grub screws 100. A
gland holder
102 carries a U-seal 104 which provides a sealing interface with an outer
surface of the
rod 84. A seal retainer 106 ensures that the U-seal remains in position. A
spring 108
acts between the structure at the lower end of the housing and the bobbin 88.
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[0038] A lower end 110 of the rod extends beyond the lower end 52 of the valve
tube
and is engaged with appropriate attachment structure 112 which fixes the lower
end 110
at a central location to the lower hemispherical end 64 of the bladder.
[0039] Figure 9 shows a slurry pumping system 120 which is based on the use of
a first
pressure vessel assembly 10A and a second pressure vessel assembly 10B each of
the
kind shown in Figures 1 to 8. Where appropriate the parts in the two pressure
vessel
assemblies are distinguished from each other by means of the suffixes A and B.
[0040] The water ports 22A and 22B are connected to a compound water manifold
30.
Similarly the slurry ports 18A and 18B are connected to a compound slurry
manifold 26
- the components 30 and 26 are those referred to in connection with Figure 1.
An outlet
from the slurry manifold is directed to a slurry pipeline 130.
[0041] An elevated slurry source 132 in the form of a tank with an internal
agitator or
impeller 134 is connected via an isolating valve 136 to the slurry manifold.
An air-filled
shock damper 140 is connected to the slurry manifold.
[0042] Water from a clean water source 150 can be pumped by means of a clean
water
pump 152 through a water meter 154 to the water manifold 124. Water from the
manifold is returned to the water source through a water meter 158. A
programmable
logic controller 160 is connected to various components of the pumping system
as is
indicated by means of dotted lines.
[0043] The water manifold includes control valves 160A and 160B, return valves
162A
and 162B, and pilot valves 164A and 164B, and 166A and 166B, respectively.
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[0044] The switch mechanism 82 shown in Figure 2 is notionally indicated in
Figure 9
and is designated 82A and 82B respectively for the two pressure vessel
assemblies.
[0045] The slurry manifold 126 includes non-return valves 180A and 180B, and
182A
and 182B, slurry drain valves 184A and 184B, and slurry purge valves 186A and
186B,
respectively. The valves 186A and 186B can be used to direct water from the
pump
152 into the pressure vessels.
[0046] The interior of each bladder 60A, 60B forms a water volume 190A, 190B
respectively of variable size depending on the extent of collapse of the
bladder. A
respective slurry volume 192A, 192B is formed inside each pressure vessel
between an
outer surface of the bladder and an inner surface of the pressure vessel.
[0047] At start-up the slurry tank 132 is filled with slurry, and the agitator
134 is
engaged. The water tank 150 is full to the required operating level and all
valves in the
system are closed. The controller 160 is used to initiate a start-up sequence
whenever
the system has been shut down and is to be restarted.
[0048] The vent valves 80A and 80B are opened for a short interval, for
example two
minutes, and the return valves 162A and 162B are also opened.
[0049] The slurry tank 132 is positioned higher than the pressure vessel so
that when
the slurry isolator valve 136 is opened slurry flows under gravity action into
the slurry
manifold 126, past the non-return valves 186A and 186B, and into the slurry
volumes
192A and 192B. If it is not possible to elevate the slurry tank, an
appropriate feed pump
arrangement is used to supply slurry to the manifold 126.
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[0050] The slurry fills each slurry volume from the bottom of each pressure
vessel and
as the slurry levels rise the bladders collapse inwardly towards the
respective valve
tubes. Air in the slurry volumes is exhausted through the vent valves 80A and
80B. Air
which may be in the bladders is exhausted via the water return valves 162A and
162B
into the water tank 150. Within a short period both slurry volumes are
completely filled
with slurry. At this point slurry flows through the vent valves 80A and 80B.
Both
bladders are fully collapsed around the respective valve tubes and each
bladder takes
up the configuration shown in Figure 8 wherein, as is further described
hereinafter, the
flow apertures 46 in the valve tubes are closed by the bladder material.
[0051] Air in the damper 140 is compressed to a maximum extent into a bubble
at an
upper end of the damper. A pressure transducer 200 reads the pressure which is
created by the difference in elevation between the transducer and the slurry
level in the
tank 132 and transmits a reading of this pressure to the controller 160. By
way of
example if the difference in elevation between the transducer and the low
level of the
slurry in the tank 132 is ten metres and the slurry has a specific gravity of
1,5 then the
pressure reading is of the order of 1,5 bar.
[0052] If the minimum pressure reading does not register with the controller
160 then
the implication is that the slurry tank is empty or that there is a blockage
in the slurry line
to the slurry manifold. The controller will then abort the start-up process. A
beneficial
point is that the pressure transducer is only in contact with air and does not
come into
contact with the slurry.
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[0053] After the initial two minute period the controller 160 causes the vent
valves 80A
and 80B, and the water valves 162A and 162B, to be closed, whereafter the pump
152
is started and the control valve 160B, the pilot valve 164B and the water
return valve
162A are opened. Water can then flow under pressure from the pump through the
meter 154 into the valve tube 34B. The water exits through the respective flow
apertures 46B and forces the bladder 60B outwardly away from the valve tube.
In the
process the slurry in the slurry volume 192B is displaced through the slurry
manifold
126 past the non-return valve 182B into the pipeline 130.
[0054] The controller 160 is driven by the water meter 154 which has a pulsed
output.
Consider that the design displacement volume of each of the bladders in their
relaxed
states, as is shown in Figure 5, is 300 litres and that the meter 154 sends a
pulse every
10 litres. Thirty pulses from the meter means that 300 litres have been pumped
into a
bladder and as a consequence 300 litres of slurry would have been discharged
into the
pipeline 130 at a pressure determined by the back pressure in the pipeline. As
the
water flows into the bladder 60B the pulses from the meter 154 continue to
register in
the controller 160. For the given example when pulse 25 is reached the
controller
causes the water return valve 162A to be closed and then, on pulse 27, it
causes the
pilot valve 164A to open. This pre-pressurises the vessel 12A to the correct
operating
pressure. During the next three pulses from the water meter discharge of
slurry takes
place from the slurry volume 192A at a rate which is determined by the size of
the pilot
valve 160A.
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[0055] Upon pulse 30 the controller 160 instructs the control valves 160A and
160B to
change state concomitantly. The pulse counter in the controller resets to zero
and then
continues to count the next thirty pulses as water flows into the other
vessel.
[0056] As a consequence of the simultaneous change of state of the control
valves
5 160A and 160B the flow of water from the pump 152 is smoothly diverted from
the
vessel 12B to the bladder 60A without any pressure spike - a benefit which is
due to the
pressure in the bladder 60A in the vessel 10A having previously been raised to
the
operating pressure by means of the function of the pilot valve 160A.
[0057] Water is now metered into the bladder 60A. When the controller 160
receives
10 confirmation that the two control valves 160A and 160B have successfully
changed
state it instructs the pilot valve 166B to open. The pressure in the vessel
10B drops to
atmospheric level and a small amount of water returns to the tank 150. After a
further
two seconds (in this example) the controller 160 causes the water return valve
162B to
open and, as a consequence, the interior of the bladder is fully vented to
atmosphere.
15 Slurry then flows into the bottom of the pressure vessel 12B i.e. into the
slurry volume
192B via the non-return valve 180B and displaces 300 litres of water in the
bladder 60B
through the valve tube 34B to the water tank 150 via the water meter 154. The
meter
pulses the controller 160 to provide an indication of the volume of water
which has been
expelled. If insufficient water is expelled then the controller stops the
system and
reports an overlap fault.
[0058] The slurry system is oversized with respect to the water pumping system
by
about 50%. This ensures that the slurry filling rate, for one slurry volume,
is completed
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well before the slurry discharge from the other slurry volume has reached 300
litres.
(The numerical values given herein are exemplary only, and are non-limiting).
[0059] The overlap in time provides a window during which pressures in the
vessels
are balanced by means of the pilot valves and during which a small flow of
slurry is
commenced so that when the full flow of water is diverted to the bladder,
which has
been pressurised, a smooth transition can be achieved without pressure spikes.
[0060] As the water flows into the bladder 60A the pulses from the water meter
154
register in the controller 160. At pulse 25 the controller closes the water
valve 162B and
the pilot valve 166B. At pulse 27 the pilot valve 164B is opened and the
vessel 10B is
pressurised to the operating pressure. On pulse 30 (in this example) the
controller is
caused to change the state of the control valves 160A and 160B whereupon the
next
cycle in the pumping sequence begins.
[0061] As the slurry flows into the slurry volume 192A a certain amount of
momentum
(kinetic energy) is built up in the slurry feed line. When the water return
valve 162A is
closed the momentum of the slurry can cause a shock wave to propagate from the
valve
162A to the slurry manifold 126 and then to the slurry feed line to dissipate
in the slurry
tank 132. This type of fluid-hammer is to be avoided. This is achieved in the
invention
because each valve tube 34A, 34B acts as a control valve wherein the flow
apertures
46A, 46B progressively shut off as the associated bladder collapses under the
action of
the slurry. As noted the slurry enters the slurry volume from a lower end and
gradually
causes the bladder to collapse from the lower end upwardly. At the upper end
of the
valve tube the flow apertures 46 are further apart and are smaller in size.
Thus the flow
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rate of the slurry is gradually reduced to a point at which the kinetic energy
of the
incoming slurry is inconsequential and the water return valve 162A, 162B can
then be
closed without giving rise to a fluid-hammer effect.
[0062] As a bladder collapses it deforms inwardly towards the centrally
located valve
tube. The slurry is denser than the water. Thus the slurry starts to deform
the lower
hemispherical end of the bladder inwardly initially to form a plurality of
radially spaced
pleats 200 (see Figure 8) which close upon themselves as the bladder material
between
apices 202 of the pleats migrates towards the closest flow apertures 46 in the
valve
tube 34. Each pleat comprises opposed sections 204 and 206 of bladder
material.
These pleats radiate from a centrally positioned core 208 of the bladder which
is in
intimate contact with, and which is thereby defined in shape by, a centrally
positioned
portion of the valve tube.
[0063] The pleats continue to form vertically from the bottom of the bladder
upwardly
and the flow apertures in the valve tube are sequentially closed by the
bladder material
as the level of the slurry rises in the slurry volume. Ultimately the upper
hemispherical
portion of the bladder is reached whereupon the pleats terminate in a mirrored
fashion
to the pleats in the lower hemispherical portion of the bladder as is shown in
Figure 6.
This controlled collapse of the bladder is dependent, at least, on the
external shape of
the valve tube. In order to guide the bladder as it deforms and to prevent
damage to the
bladder material it is desirable thus for the valve tube to have the nominally
flat outer
surfaces 38 with the apices 40 between adjacent surfaces. These structural
features
help in the formation of the bladder shape as it collapses. Also the flow
passages 46
have surrounding arcuate side walls 48 which extend inwardly towards an
interior of the
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valve tube with inner edges 48X well set back so that the likelihood of
bladder damage
arising when the bladder has been fully collapsed and bears hard against the
valve
tube, is much reduced.
[0064] The switch mechanism 82 shown in particular in Figure 2 is used to
reduce the
likelihood of the bladder being damaged if it is over-pressurised. The bladder
is made
from a highly elastic material and thus can be elongated by a factor of up to
eight. If the
bladder is over-pressurised it is quite possible for the bladder to be
extruded through the
slurry port 18 and into the slurry manifold - an event which would cause
destruction of
the bladder. The switch mechanism 82 is intended to prevent this from
occurring.
Ideally the bladder should be deformed in a radial sense only i.e. between the
relaxed
position shown in Figure 7 and the collapsed configuration shown in Figure 8.
For this
type of operation the bladder length is not extended to any meaningful extent.
If
however a malfunction occurs then the bladder, once fully expanded in a radial
sense,
initially abuts an inner wall of the pressure vessel but, thereafter, further
pressurisation
causes the length of the bladder to be increased. If this occurs the rod 86,
which has
one end attached to a central position of the lower hemispherical end of the
bladder, is
moved downwardly inside the housing 94 against the bias of the spring 108.
Movement
of the switch bobbin 88, attached to the upper end of the rod, is detected by
the sensor
92 and an alarm signal is directed to the controller 160 which stops
functioning of all
components of the slurry pumping system. All valves then revert automatically
to
closed positions.
[0065] The pumping system of the invention possesses significant advantages
compared to conventional centrifugal slurry pumps, which include the
following:
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19
elimination of glands or rotating seals operating in slurry;
no gland service water pump;
no gland service water cost;
no pumps operating in slurry;
no control instrumentation in slurry;
immediate detection of any malfunction;
each bladder has a high service life for the bladder material has an
elongation factor of
about 800% and in use is only subjected to stretch of 10% maximum - thus the
material
is virtually stress free;
use is made of only one direct coupled, high efficiency, multi-stage, clear
water pump
(152), with a mechanical seal, as an energy source. This pump exhibits better
efficiency and a lower power consumption than a conventional centrifugal
slurry pump
arrangement with an equivalent pumping capacity;
consistent pumping efficiency;
widely variable flow capability;
inbuilt accounting system - the volume of slurry displaced is equal to the
measured
volume of clear water pumped;
consistent density of slurry is delivered;
virtually unlimited pressure possibility as no booster pump stations required;
and
the length to diameter ratio and design of the pressure vessels result in
inexpensive
manufacture.
[0066] The capacity of the system is readily increased by extending the length
of each
pressure vessel, which is comparatively inexpensive, as opposed to increasing
the
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diameter of a vessel, which is expensive. As each pressure vessel is of
integral welded
construction, connecting flanges are not required. The upper opening in the
vessel is
dimensioned so that the bladder and valve tube can be located inside the
vessel by
being passed through the opening, at the upper end, to which the flange 76 is
fixed.
