FIELD

This specification relates to inlet end assemblies for double-acting hydraulic ram liquid suction pumps, e.g. for pumping water from wells, boreholes and the like.

BACKGROUND

Suction rams may be divided into two broad categories, single acting and double acting, as follows:

Single Acting: Those having a single drive pipe and delivery pipe, an impulse valve between the drive pipe and delivery pipe, and a single intake non-return valve situated immediately downstream of the impulse valve. Most examples incorporate an accumulator connected to the bottom of the drive pipe to store the kinetic energy in the drive pipe and to limit damage to the apparatus due to the production of un-exploited discharge shock waves. Examples are described in US799428, DE804288, US4948341, and AU708806.

Double Acting: Those having a single drive pipe but two delivery pipes, each connected to an intake non-return valve. The impulse valve is a diverter valve such that, in operation, at any one time one of the two delivery pipes is closed but not the other. Examples are described in FR435032, US3123009, US4121895, WO2010/130002, and WO20 18/042188.

There is a general need to improve the hydraulic efficiency of double-acting hydraulic ram liquid suction pumps. Also these pumps can have difficulties self-starting. One solution is to provide a pulse in the drive flow aimed at triggering the diverter valve to actuate, but improved solutions are desirable.

SUMMARY

In a first aspect there is described an inlet-end assembly for a double-acting hydraulic ram suction pump comprising a drive inlet port to receive a liquid drive flow for the pump and first and second exit ports to provide pumped liquid, each connected to an inlet via a respective non-return inlet valve. The exit ports may have a shared inlet or separate inlets. The inlet-end assembly may further comprise a diverter valve, e.g. in a diverter valve chamber, in fluid communication with the drive inlet port. The diverter valve may comprise a pair of diverter valve ports, each coupled to a respective exit port, and a self centring closure between the diverter valve ports, able to move to selectively inhibit fluid flowing from the drive inlet port into one or other of the diverter valve ports. The inlet- end assembly may further comprise an elastic chamber, e.g. an elastic bulb, in fluid communication with the diverter valve.

Such an arrangement can facilitate self-starting with any drive flow sufficient to generate a pumping effect, without reliance upon a sudden or characteristic rise or pulse in drive flow. Further, in such an arrangement the valves can switch between fully open and fully closed positions extremely rapidly and with minimal actuation force, so as to minimise rise and fall times of flows through the valve(s), minimise pinching-losses and back-flows during the valve actuation. Still further, such an arrangement can help give the components a long lifetime. It is important that all components should have as long a service life as possible in normal operation, which may involve pumping water heavily loaded with suspended solids and corrosive solutes. In many applications, such as lifting well water for smallholder farmers in developing countries, it is also desirable that this should be achieved with a minimal mass of materials using the cheapest materials suited for the application. Still further, such an arrangement can reduce a frequency of maintenance required.

The self-centring closure may be configured to enable the closure to swing back and forth between the diverter valve ports. For example, the closure may rotate or translate back and forth between the diverter valve ports.

In some implementations the self-centring closure comprises a blade flexure, e.g. a flexure spring having the form of a flat sheet of material, similar to a cantilever spring. The blade flexure may be mounted so that it is biased towards a central position between the diverter valve ports and flexes (driven by liquid flow though the diverter valve) to selectively inhibit fluid flowing from the drive inlet port into one or other of the diverter valve ports, thereby actuating the diverter valve. The blade flexure may be clamped at one end and have a valve port seal at an opposite end, although it is not essential that a valve port seal is used. The blade flexure may narrow away from the fixed end, e.g. it may have a trapezoidal shape, to reduce flutter and tearing forces at the fixed end cantilever. The blade flexure may have a cut-out to reduce viscous drag and consequential higher-order bending stresses in the flexure.

In some implementations the self-centring closure comprises a valve closing member mounted to enable rotation about a valve member axis to selectively close one or other of the diverter valve ports. The valve closing member may be biased towards a position in which both of the diverter valve ports are open. In implementations the valve closing member is mounted on a self-centring hinge or bearing.

In some implementations the closure is configured to move in a direction perpendicular to a longitudinal axis of the inlet-end assembly. For example the valve member axis may be aligned along a direction of, e.g. parallel to, this longitudinal axis, or the blade flexure may be clamped or fastened along this longitudinal axis. Such a configuration facilitates efficient use of space within the assembly.

In some implementations the closure is configured to move in a direction perpendicular to a transverse axis of the inlet-end assembly. For example the valve member axis may be aligned transverse to a longitudinal axis of the inlet-end assembly, or the blade flexure may be clamped or fastened along this transverse axis. Such a configuration can reduce unwanted shear forces on the blade flexure or value closure member. For example, where a drive flow received via the drive inlet port is incident on the diverter valve from above, the transverse axis may lie across the drive flow, rather than along the drive flow where it would result in a shear force on the blade flexure/value closure member. This arrangement can therefore increase a lifetime of the self-centring closure.

In some implementations the inlet-end assembly is generally cylindrical. As used herein “cylindrical” includes approximations to a cylindrical shape.

The inlet-end assembly may have a diverter valve chamber in which the diverter valve is located. In implementations the diverter valve chamber is in fluid communication with both the drive inlet port and the elastic chamber. The elastic (compliant) chamber may be partially or wholly located on an opposite side of the diverter valve to the drive inlet port or, in implementations, below the diverter valve chamber (or diverter valve) and the drive inlet port, e.g. the elastic (compliant) chamber may be at an opposite end of the inlet-end assembly to the drive inlet port and first and second exit ports. This can facilitate allowing the elastic chamber to flex in an axial direction of the assembly, enhancing the compliance provided by the elastic chamber. More specifically, an advantage of allowing the elastic chamber to flex axially as well as radially is that the elastic chamber may be fabricated from less material or from a material of lower strength as a size of the elastic chamber can be reduced. It can also help avoid a need to use different lengths of pipe for different applications, enabling the assembly to be more widely used.

In some implementations the diverter valve chamber may be within the elastic chamber. In some implementations the diverter valve chamber and the elastic chamber may be the same chamber. In some other implementations the diverter valve chamber and the elastic chamber may be different chambers in fluid communication with one another, e.g. the elastic chamber may comprise an elastic bulb in fluid communication with the diverter valve chamber. In some implementations a fluid path from the diverter valve chamber smoothly opens into the elastic chamber to provide a substantially swept fluid communication path between the elastic chamber and the diverter valve chamber. The swept fluid communication path may be a fluid communication path which substantially minimizes dead zones/fluid entrapment regions and which has generally low shear.

In some implementations the inlet, which may be referred to as an assembly inlet, is in fluid communication with each of the non-return inlet valves is located between the diverter valve chamber and the elastic chamber. The (assembly) inlet may be configured to allow pumped liquid to be taken in radially during a pumping cycle.

In some implementations the assembly comprises a protective shroud for the elastic chamber. The shroud may have perforations to facilitate a change in volume of the elastic chamber within the shroud. The shroud may cover the (assembly) inlet and have first perforations for fluid ingress to the (assembly) inlet and second perforations to facilitate a change in volume of the elastic chamber within the shroud. The first perforations screen out and inhibit debris from entering the assembly; the second perforations facilitating achieving a large compliance from the elastic chamber/bulb. In some implementations the shroud has a two-piece, e.g. modular construction. The elastic chamber may be supported within the shroud by a ring or guide, optionally an elastic ring or guide e.g. with a hollow or cross-shaped cross-section. This facilitates the elastic chamber/bulb moving both axially and radially within the shroud without chafing, again facilitating achieving an appropriate compliance with minimal material to endure a required operating pressure. It also reduces abrasion, hence increasing a lifetime of the elastic chamber/bulb, and allows larger manufacturing tolerances.

The above features of some implementations can facilitate hydrodynamic performance e.g. by efficient use of available space (facilitating increased flow/power or increased hydrodynamic efficiency at a given flow/power), in particular where the inlet-end assembly is cylindrical, and by reducing friction losses. The above features can also facilitate efficient starting and operation of a pump, by facilitating the provision of as much compliance as possible per unit volume and per unit mass (of the elastic material) of the compliant element e.g. elastic chamber/bulb. The above features can further facilitate locating the compliant element close to the diverter valve, which is also useful for efficient starting and operation of the pump. In addition these features can allow the size and cost of the compliant element to be reduced. A still further advantage of the above described features is to facilitate ease of maintenance e.g. easy removal of individual components for inspection and repair or replacement if required.

In some implementations the self-centring closure is sufficiently stiff that the closure does not close the diverter valve ports until a drive flow rate through the assembly is greater than approximately where g is the acceleration due to gravity, A is a cross sectional area of an exit pipe connected to one of said exit ports, h is the total pumping head in metres and c is a (modified) speed of sound within the fluid contained in the exit pipe.

Put differently, in implementations the inlet end assembly is configured such that the closure does not close the diverter valve ports until a drive flow rate through the assembly is greater than approximately where h is a specified pumping head of the assembly.

That is, a process of designing the inlet end assembly may involve selecting the stiffness of the self-centring closure so that it does not close the diverter valve ports until a drive flow rate through the assembly is greater than approximately The process may involve making the inlet end assembly to this design. In general this flow rate generates a force on the closure that is greater e.g. at least 2 times or 5 times greater, than a gravitational force acting on the self-centring closure e.g. due to a weight of parts of the diverter valve. For example in a configuration in which the valve member axis is aligned transverse to a longitudinal axis of the inlet-end assembly, in general gravitational force is insufficient to close the diverter ports, and the inlet end assembly is configured so that for the specified pumping head h the closure does not close the diverter valve ports until a drive flow rate through the assembly is greater than approximately — .

Equivalently the self-centring closure is sufficiently stiff that the closure does not close the diverter valve ports until a flow rate through the assembly is sufficient to provide a pressure reduction at either exit port greater than or equal to pgh where p is the density of the pumped medium, g is the acceleration due to gravity and h is the total pumping head in metres. The pressure reduction may be defined as a pressure reduction between either diverter valve port and the respective exit port; in use the pressure reduction is for a short period of time during a cycle.

More exactly the self-centring closure is sufficiently stiff that the closure does not close the diverter valve ports until the maximum flow rate through either said exit port exceeds Here the flow rate referred to is equal to the peak flow rate through each of the exit ports (the drive flow rate is approximately half this value).

In some implementations one or more of the non-return inlet valve and diverter valve comprise parts made from cavitation-resistant material e.g. nylon or acetal moulded parts. It has been found that, in practical applications, the longevity of valve and other parts in a double-acting hydraulic ram suction pump is limited by cavitation and consequent pitting. This can be addressed by fabricating such parts, e.g. a valve part which is intended to seal against another part such as a valve seat/block or valve port seal, from cavitation-resistant material. Such materials may include nylon, in particular glass-filled nylon, and acetal, e.g. glass-filled acetal. Susceptibility to cavitation damage occurs in the close vicinity of the moving valve parts in the diverter valve and inlet valves, and cavitation and impact resistant materials are particularly useful in these locations. Thus in another aspect there is provided a double-acting hydraulic ram suction pump including one or more valves with valve parts, such as a valve seat/block or valve port seal, made from cavitation-resistant material.

In a further aspect there is provided a double-acting hydraulic suction ram pump. The double-acting hydraulic suction ram pump may comprise a diverter valve chamber comprising two rising exit ports for connecting to riser or delivery pipes and one drive inlet port for connecting to a drive pipe, the two rising exit ports and one drive inlet port being arranged e.g. in a triangular configuration on the top of the chamber.

The double-acting hydraulic suction ram pump may further comprise two valve blocks comprising respective valve-seats contained within the diverter valve chamber. Each valve block may be connected to one of the rising exit ports at the top and to a non-return inlet valve at the bottom thereof to allow fluid to be sucked into the pump. Each valve block may have a swept diverter valve port to one side thereof.

The double-acting hydraulic suction ram pump may further comprise a diverter valve within the diverter valve chamber and comprising a self-centring closure. The self centring closure may be located below the said drive inlet port and between the respective swept diverter valve ports of the two valve blocks. In implementations the self centring closure comprises a flexure-spring supporting a valve port seal.

The double-acting hydraulic suction ram pump may further comprise an elastic bulb connected to the diverter valve chamber by a connecting conduit or adapter in fluid communication with the diverter valve and drive inlet port and in switching communication with each one of said rising exit ports. The elastic bulb may be partly or wholly situated below the diverter valve and pump inlet valves and may be mounted to allow the elastic bulb to flex both axially and radially.

BRIEF DESCRIPTION OF FIGURES

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which: Figure 1 is a schematic diagram of an example inlet-end assembly of a double-acting hydraulic ram suction pump.

Figures 2a-2c show the inlet-end assembly of Figure 1 in use, illustrating phases of normal operation.

Figures 3a and 3b are schematic diagrams of another example inlet-end assembly.

Figures 4a and 4b show a three-dimensional model of an example inlet-end assembly.

Figures 5a to 5c show a three-dimensional model of an example inlet-end assembly corresponding to that of Figure 4, sectioned in 3 orthogonal planes.

Figures 6a and 6b are schematic diagrams illustrating example closure movement alignments for the inlet-end assembly.

Figures 7a and 7b are schematic diagrams illustrating alternative arrangements of a compliant chamber.

Figures 8a and 8b show, respectively, an isometric view and a cross-sectional view of a three-dimensional model of an example inlet-end assembly with a protective shroud.

Figure 9 a schematic diagram of an example inlet-end assembly including a sealed chamber.

DETAILED DESCRIPTION

This specification generally relates to hydraulic suction ram pumps which enable fluids to be lifted from above, particularly from beyond suction depth. Generally hydraulic suction ram pumps are employed to enable surface-level water pumps to draw water from deep wells or boreholes in which the water level is beyond suction depth (theoretically over 10m, but in practice around 7-8m). This specification relates particularly to hydraulic suction ram pumps of the type that employ a diverter valve and two rising pipes, which can help avoid stalling scenarios in which all rising pipes are blocked.

Referring to Figure 1, this shows an example cylindrical inlet-end assembly 1 for a double-acting hydraulic ram suction pump. The assembly comprises a drive inlet port 2, to receive a liquid drive flow for the pump, and first and second exit ports 3,4 to provide pumped liquid. Each of the first and second exit ports is connected to an inlet 5 via a respective non-return inlet valve 6, 7. In some other implementations there may be two inlets, one connected to each inlet valve but that are not otherwise connected.

The assembly may further comprise a diverter valve in fluid communication with the drive inlet port. In some implementations the diverter valve is located, as shown, in a diverter valve chamber 8. The diverter valve may have a pair of diverter valve ports 9,10, each coupled to a respective exit port.

In implementations the diverter valve comprises a self-centring closure 11, located between the diverter valve ports and able to move to selectively inhibit fluid flowing from the drive inlet port into one or other of the diverter valve ports.

In implementations the inlet-end assembly 1 also comprises an elastic, i.e. compliant, chamber 12, e.g. an elastic bulb, in fluid communication with the diverter valve, e.g. with the diverter valve chamber. The elastic chamber may be partially or wholly located on an opposite side of the diverter valve (or diverter valve chamber) to the drive inlet port.

In the example of Figure 1 the drive inlet port 2 and exit ports 3,4 are arranged side by side and the two non-return inlet valves 6, 7 are both shown in an open position for clarity. However in some implementations the drive inlet and exit ports may be arranged in a triangular pattern, for compactness. During operation at least one inlet valve would normally be closed.

Referring to Figures 2a-2c, Figure 2a shows drive liquid flowing into the inlet-end assembly 21 through drive inlet port 22, around self-centring closure 211 and diverter valve ports 29, 210, and out through both exit ports 23, 24. The pump may be operated so that the drive flow-rate is too small to excite oscillations (though turbulence or otherwise) in the self-centring closure 211, but large enough to permit impacts of the self-centring closure against either of the diverter valve ports 29, 210 to close the respective ports.

The self-centring force per unit displacement from a central position of the self-centring closure may thus be selected or adjusted to inhibit such impacts when the drive flow-rate is smaller than a value which is sufficient to affect pumping (e.g. by the Joukowski effect), with the purpose of minimising component wear.

A “central” or quiescent position of the self-centring closure may be arranged to be slightly off-centre with respect to the diverter-valve ports. Such an asymmetry is useful for initialising oscillations in the closure at a lower starting flow, which can be helpful for starting the pump.

When the drive flow is sufficiently large oscillations commence as shown in Figure 2b. This shows the assembly in normal operation at an inlet phase of the cycle, where the self-centring closure 211 is substantially sealed over one of the diverter valve ports 29. Figure 2c shows normal oscillations at another inlet phase of the cycle where it is substantially sealed over the other diverter valve port 210.

The seal does not have to be perfect and some leakage is tolerable. For example in some implementations the closure only partially seals the diverter valve ports but has greater durability than would otherwise be the case.

Figure 3a, and Figure 3b which illustrates the assembly of Figure 3a in operation, show a configuration in which the non-return inlet valves 36, 37 are of the poppet-type and arranged substantially coaxially with, and underneath the two exit ports 33, 34. As with Figure 1, the components have been arranged to show the drive inlet port 32 and exit ports 33, 34 side by side, though in practice they may have a triangular arrangement. In Figure 3a, the two non-return inlet valves 36, 37 are both shown in an open position for clarity (this would typically not be the case during normal operation). Figure 3b illustrates an inlet phase of the cycle in which self-centring closure 311 is substantially sealed over one diverter valve port. Figures 4a and 4b show an arrangement in which the drive inlet port 42 and exit ports 43, 44 are arranged in a triangular, e.g. an equilateral triangle, configuration. In a variant an isosceles triangle configuration may be used, for example if the ports are connected to pipes of different diameters. Above a minimum flow rate related to the minimum flow velocity at which the inlet valves can open due to the Joukowski effect, this configuration helps to achieve high hydraulic efficiency for a given power or flow rate by allowing the diameter of the pipes to be maximised. It is advantageous for the inlet-end assembly to have a minimum external (envelope) diameter in proportion to the diameter of the pipes connected to the pump, so that a pump of a given capacity can fit into the smallest diameter boreholes, or the greatest pump capacity possible can be used in any given borehole.

Hosetails may be connected to the ports to facilitate connection to pipes, or threads or other connection means may be provided. A “keeper plate” arrangement 420 may be used to retain the hosetails or other connection means against the ports, facilitating easy removal of pipes from the inlet-end assembly, for example for inspection and maintenance.

In the example of Figures 4a and 4b the diverter valve chamber comprises a thin-walled diverter valve can 48. Inlet 45 comprises a connection from the diverter valve chamber to an elastic (compliant) chamber, e.g. comprising an elastic bulb 412.

Figure 4b shows the example of Figure 4a with the diverter valve can 48 removed to show the components contained within. The diverter valve can may be sealed from the exterior at the top and bottom by top flange 430 and base flange 440 respectively.

The base flange may comprise a port 450 connecting the diverter valve can through to the compliant chamber (elastic bulb). In implementations the base flange also comprises other ports (not shown in Figure 4b).

Two valve blocks 441, 442 are situated in the diverter valve can between the top and base flanges, comprising diverter valve ports 49, 410. The valve blocks may each be permanently joined to one of the flanges, or they may be independent components sealed against the flanges with O-rings or by other sealing means. They may be arranged to couple each exit port 43, 44 to inlet 45 via ports in the base flange. It has been found that cavitation can be a problem in practical implementations of the inlet-end assembly. Thus in implementations the valve blocks may be made from a material which has a combination of high cavitation resistance and high impact strength. It has been found in practice that a nylon material, in particular glass-filled nylon material, or an acetal polymer material is satisfactory.

Thus in implementations the non-return inlet valve and/or diverter valve e.g. diverter valve ports, comprise nylon or acetal moulded parts. The flanges 430 and 440 and inlet 45 may be fabricated from a different material, in particular a UV-stabilized material such as UV-stabilised glass filled polypropylene or glass filled high-density polyethylene.

The ports may each comprise elastomeric sealing means to improve sealing, buffer impact forces and minimise stiction effects. That is, one or more of the ports may have an elastomeric seal. Elastomeric seals may also or instead be located elsewhere, for example, as part of self-centring closure 411 e.g. on a part of the closure which closes a diverter valve port. The ports may be configured to seal substantially along a line to minimise stiction effects, whether or not elastomeric seals are employed.

Referring now to Figures 5a-5c, these show details of an example self-centring closure 511 and some of the ports. Figure 5a shows a section along the axis of the cylindrical assembly through drive inlet port 52, inlet 55, self-centring closure 511, and elastic chamber 512. Figure 5b shows a section perpendicular to the axis of the assembly and through diverter valve chamber 58, diverter valve ports 59, 510, and a lower part of the self-centring closure 511. Figure 5c shows a section along the axis of assembly through exit ports 53, 54, inlet 55, non-return inlet valves 56, 57, and elastic chamber or bulb 512.

In the example of Figures 5a-5c the self-centring closure 511 comprises a flexure spring e.g. a blade flexure 530, clamped and rigidly held by a cantilever block and clamp 531 and a valve port seal 532 at the opposing end of the blade flexure. The valve port seal 532 may be made from a polymer e.g. nylon or acetal and/or an elastomer; and/or it may include a metal component.

In normal operation, the valve seat orbits the cantilever block approximately along an arc, permitting it to seal selectively against the diverter valve ports 59, 510 contained within the valve blocks 541, 542. The valve blocks and/or other components may be manufactured from materials exhibiting a desirable combination of cavitation resistance and impact stress resistance, for example, an appropriate grade of nylon or a nylon composite. The valve seat may be constructed from an impact-resistant material and may be configured to seal substantially along a line to minimise stiction effects.

The flexure spring, e.g. blade flexure, may be tapered to inhibit tearing at the cantilever and to reduce or discourage second-order oscillatory modes such as flutter. It may include a relief hole or cut-out to reduce viscous drag and minimise undesired bending stresses associated with this or other causes, for example, those which might result in higher-order deflections resulting in an undesirable seating angle of the valve seat, or which might give rise to stresses in the blade flexure beyond its fatigue limit. Baffles or other flow-guiding means may optionally be included within the diverter valve chamber to minimise destructive hydrodynamic forces on the diverter valve, for example shear forces or forces that may promote tearing or stress cracking.

In some alternative arrangements, a hinge or bearing may be used. Then a self-centring force may be provided by bias means such as one or more torsion springs, or standard (linear travel) compression or expansion springs. Alternatively a torsion bar, torsion spring, elastomer, or other means of arranging a centring (bias) force may be used, with or without a hinge or bearing.

In the example of Figures 5a-5c, inlet 55 comprises a swept connection 551 between diverter valve can 58 and elastic bulb 512. In operation, the elastic bulb is unconstrained in both radial and axial directions along most of its length with the result that it may be minimised in size and mass to achieve a given compliance for a given service pressure. The elastic bulb may be formed at least partly from a stiff elastomeric material such as a thermoplastic elastomer or other elastomeric material.

In Figures 5a-5c ports in the base flange connected to the valve blocks comprise non return inlet valves 56, 57 coupled to the inlet 55 and the respective valve blocks 541 , 542.

Figures 6a and 6b illustrate operation of an example cylindrical inlet-end assembly. These schematic diagrams illustrate alternative alignments of a self-centring closure which uses a hinge or bearing. However a blade flexure-based self-centring closure may be arranged with corresponding alignments, although the path traced by movement of a valve port seal, such as a flap at the end of the blade flexure (flexure spring), is not circular - in effect the movement is a combination of rotation and translation.

Figure 6a shows a self-centring closure 611 that comprises a valve closing member mounted for rotation about a valve member axis 621 (into the page). In Figure 6a the valve member axis is aligned along a direction of e.g. parallel to a cylinder axis 631 (also into the page) of the cylindrical inlet assembly, and in this example also along a direction of an axis 641 of the drive inlet port 62. An advantage of this alignment is to facilitate a close form-fit with the approximately “wedge-shaped” space available for the self centring closure within diverter valve can 68 and between diverter valve ports 69, 610. This facilitates maximising one or more hydraulic diameters of the flow channels between the drive inlet port and the diverter valve ports within the limited space available.

In Figure 6b, a valve member axis 661 of valve closing member 651 is aligned perpendicular to a cylinder axis 671 of the cylindrical inlet assembly or an axis of the drive inlet port, to minimise bluff-body forces transverse to the direction of valve movement between diverter valve ports 619, 629. An advantage of this alignment is that it can minimise undesirable hydrodynamic “bluff-body” forces due to cross-flows substantially perpendicular to the direction of valve movement. These can otherwise increase friction wear or lead to component damage, for example, tearing of the blade flexure spring(s).

Thus in Figure 6a the closure moves in a direction perpendicular to a longitudinal axis of the cylindrical inlet-end assembly whereas in Figure 6b the closure moves in a direction perpendicular to a transverse axis of the cylindrical inlet-end assembly. In an arrangement where the closure comprises a blade flexure (flexure spring) the closure may similarly be arranged to move in a direction perpendicular to either a longitudinal or transverse axis of the cylindrical inlet-end assembly.

In other arrangements the valve member axis (closure movement) may be aligned in a direction intermediate between those of Figures 6a and 6b, for example to optimise a trade-off between the advantages and disadvantages of either alignment. In some applications there is a tight constraint on a diameter of the cylindrical inlet assembly. For example the inlet assembly may be required to operate efficiently in a narrow borehole. In some applications it is possible to relax this constraint, for example if the assembly is to operate in wells or boreholes with an internal diameter significantly greater than the minimum diameter at which the pump can operate efficiently, or at a flow rate significantly lower than the maximum flow rate at which it can operate efficiently. Relaxing the diameter constraint can facilitate a reduction the number, mass, and cost of the components used. Also an axial length or height of the assembly may be reduced which can be useful, for example, when a difference between the dug or drilled depth, and the water level in a well or borehole is small.

Thus as shown in Figures 7a and 7b, in some implementations a self-centring closure 711 and/or diverter valve ports 79, 710 may be located substantially within the compliant (elastic) chamber 712. In Figure 7a, inlet 75 and non-return inlet valves 76, 77 are located in the lower part of or at least partly below the compliant (elastic) chamber. This provides an advantage that they may easily be accommodated in this location e.g. without interrupting a drive flow between the diverter valve ports and the exit ports; the elastic chamber may be cheaply made by extrusion.

In Figure 7b non-return inlet valves 76, 77 are located in the upper part of the assembly, or at least partly above the compliant (elastic) chamber 712. This facilitates allowing the compliant (elastic) chamber 712 to flex in both a radial and an axial direction with advantages as previously described, i.e. lower material mass and associated cost, and facilitating manufacture by injection-, rotational- or blow-moulding.

Inlet 75 may be located below the self-centring closure 711 and diverter valve ports 79, 710, as shown in Figure 7a, or it may be located above the self-centring closure 711 and diverter valve ports 79, 710, as shown in Figure 7b. More generally, the diverter valve can and compliant (elastic) chamber may be combined into a single compliant diverter can or bulb.

Figures 8a and 8b show, respectively, an isometric view of an example inlet-end assembly with a protective shroud 813, and a cross section thereof passing through drive inlet 82 and self-centring closure 811. It is often desirable to protect the compliant chamber from damage during operation, for example due to repeated impacts or friction wear against the sides of a well or borehole, or damage incurred during installation. As shown in Figures 8a and 8b, a shroud 813 may be installed over at least part of compliant chamber 812. This may be constructed from two halves as shown in figure 8, or otherwise - for example, as a single closed-tube assembled from below, or in three or more parts. The shroud may have an inlet screen 814 to prevent large particles, such as those capable of causing blockage or damage, from entering the assembly. In operation, the volume between the compliant chamber and the shroud may be filled with water or another incompressible fluid. Thus the shroud may include “relief” slots 815 along its length to allow for the rapid movement of said incompressible fluid into and out of the shroud to minimise pressure pulses which can reduce efficiency and cause damage in operation.

The compliant (elastic) chamber may comprise an elastic bulb. In use the elastic bulb may flex both axially and radially, but where the elastic bulb is mounted inside a shroud wear can result. A solution to this is to install a guide ring or bush 816, such as an X- ring, quad-ring, quad-seal, or similar, between compliant chamber 812 and shroud 813. This can facilitate alignment on assembly and reduce frictional wear of the compliant chamber against the shroud which might occur, for example, due to axial misalignment. A gap or “relief-channel” 817 may be provided on the inside of the shroud in the vicinity of the guide ring or bush 816 to allow it to run smoothly along the inside of the shroud, for example, during longitudinal expansion and contraction of compliant chamber 812 along a cylinder axis.

A shroud similar to that described above with reference to Figure 8 may be provided for the other example arrangements described herein.

Figure 9, is a schematic diagram of an example inlet-end assembly that includes a sealed chamber 900 around compliant chamber 912, arranged to contain a trapped volume of gas 990, e.g. air or nitrogen. The inlet-end assembly of Figure 9 is generally similar to that shown in Figures 3a-3c, but such a sealed chamber may be provided for any of the inlet-end assemblies described herein, including those of Figures 6 and 7.

The trapped gas 990 may surround compliant chamber 912 instead of or in addition to a shroud, to provide external support thereto. This can be useful in very deep wells and/or at very high flow rates where a time averaged pressure inside the compliant chamber may otherwise exceed the burst pressure of the compliant chamber. Where a sealed chamber is provided the compliant chamber may comprise an elastic bulb with substantially thinner walls or be significantly more elastic than arrangements without a sealed chamber might otherwise allow. Conversely, it may be less elastic and arranged instead as a collapsible bag or bellows, to fold or pleat instead of or as well as stretch and relax beyond its natural un-pressurised form. In either case, the intention may be that compliant impedance is provided substantially by gaseous compression and expansion of the trapped gas instead of elastic elongation and contraction of the elastic bulb. Means e.g. a valve such as a capillary or snifting valve may be arranged to facilitate replenishment of the trapped gas from a surface level or otherwise, for example, due to the gradual loss thereof due to permeation or slow leaks. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.