WO2010017567A1

WO2010017567A1 - Pumping system

Info

Publication number: WO2010017567A1
Application number: PCT/ZA2009/000071
Authority: WO
Inventors: Richard Roy Wood
Original assignee: Richard Roy Wood
Priority date: 2008-08-03
Filing date: 2009-08-03
Publication date: 2010-02-11
Also published as: ZA201101489B; RU2011104247A; CA2736856C; AU2009279417B2; AU2009279417A1; CA2736856A1; CL2011000231A1; RU2519681C2

Abstract

A pumping system which includes two pressure vessels each of which has an internal flexible bladder, a water manifold, a pump for pumping water trough the water manifold alternately into the bladders, a slurry manifold through which slurry is expelled alternately from each vessel as the bladder is expanded and a control system which pressurises one bladder with water shortly before the other bladder is fully collapsed, and vice versa.

Description

PUMPING SYSTEM

BACKGROUND QF 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] Siurry 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 siurry 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, WO97/49897, US3951572, US2002/0011579 and WO2006/076827. [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.

[0008] 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 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 vaive 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 vaive 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. [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. [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 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, 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 siurry 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 piiot 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. 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. 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 vessei 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 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 iower 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 CD- ring seal, which is integral with the tubular mouth. The tubular mouth is positioned 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 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 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. [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. [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 6OA, 6OB 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 8OA and 8OB 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. [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 8OA and 8OB. 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 8OA and 8OB. 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. [0053] After the initial two minute period the controller 160 causes the vent valves 8OA and 8OB, 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 biadder 6OB outwardiy 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 6OB 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. [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 160A and 160B the flow of water from the pump 152 is smoothly diverted from the vessel 12B to the bladder 6OA without any pressure spike - a benefit which is due to the pressure in the bladder 6OA 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 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. 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 6OB 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 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 fiow 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 6OA 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 controi 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 fiuid-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 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 inwardiy towards the centraiiy 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 pieats 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 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: 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 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.

Claims

1. A pressure vessel assembly 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 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

2. A pressure vessel assembly which includes a sensor for detecting elongation of the bladder, inside the pressure vessel, beyond a predetermined position.

3. A pressure vessel assembly according to claim 2 wherein the sensor 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 movement of the elongate member from a predetermined position.

4. A pressure valve assembly according to claim 1 , 2 and 3 wherein the valve tube has a plurality of longitudinally extending sides and each side has a number of the flow apertures, and wherein each flow aperture is bounded by a respective arcuate surface which extends towards an interior of the valve tube.

5. A pressure valve assembly according to any one of claims 1 to 4 wherein the total 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.

6. A pressure valve assembly according to any one of claims 1 to 5 wherein the valve tube and bladder are configured so that, upon collapse, the bladder has an elongate central core which abuts the vaive tube, and a plurality of elongate pleats which extend radially from the core and which are angulariy 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.

7. A pressure valve assembly according to any one of claims 1 to 6 wherein the first fluid is water and the second fluid is slurry.

8. A pumping system which includes first and second pressure vessel assemblies, such pressure vessel assembly being according to any one of claims 1 to 6, 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 second fluid ports of the pressure vessels, and a controller which regulates operation at least of the first fluid manifold so that second fluid flows through the second fluid manifold, during a pumping cycle, into at least the second fluid volume of the first pressure vessel assembly 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.

9. A pumping system according to claim 8 which includes a damper which contains a gas at a pressure which is dependent on the level of the second fluid in a second fluid feed tank.

10. A pumping system according to claim 8 or 9 wherein, as the second fluid flows into the second fluid volume, the bladder of the first pressure vessel assembly is caused to collapse from the lower end of the bladder towards the upper end of the bladder so that the flow apertures in the valve tube are closed successively from the lower end to the upper end of the valve tube.

11. A pumping system according to claim 8, 9 or 10 wherein, prior to the end of the pumping cycle, the pump pressurises the bladder of the first pressure vessel assembly.

12. A pumping system according to any one of claims 8 to 11 wherein the first fluid is water and the second fluid is slurry.

13. A bladder for use in the pressure vessel assembly of claim 1 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.