Patent Description:
Cone valves are often used to regulate the flow of medium, particularly a medium which consists of a mixture of liquid and solid particles, such as a slurry.

One application where this occurs is in pressure exchange chamber ("PEC") pumping systems. A PEC pumping system typically includes a pipe defining a PEC and having a medium or pumped fluid valve arrangement at one end and a driving fluid valve arrangement at the other end. The medium valve arrangement includes a medium inlet valve whereby medium to be pumped can be admitted into the pressure exchange chamber and a medium outlet valve whereby pumped medium can be discharged from the PEC along a discharge pipe, riser, or the like. Similarly, the driving fluid valve arrangement includes a driving fluid inlet valve through which a high-pressure driving fluid can be admitted into the PEC and a driving fluid outlet valve whereby driving fluid can be discharged from the PEC.

In use, medium to be pumped may be fed to the medium inlet valve at a relatively low pressure by means of a medium delivery pump, such as a centrifugal pump. With the medium inlet valve open and the driving fluid outlet valve open medium enters the pressure exchange chamber and displaces driving fluid out of the PEC through the driving fluid outlet valve. Although the medium to be pumped is fed into the PEC at a relatively low pressure, if the PEC is located on a sea bed, the ambient pressure may be high, but it will be lower than the pressure of the high pressure driving fluid.

When the PEC has been charged with medium, i.e., a desired quantity of medium has entered the PEC, the medium inlet valve and driving fluid outlet valve are closed. The medium outlet valve and the driving fluid inlet valve are opened such that driving fluid enters the PEC at high pressure and displaces the medium out of the PEC through the medium outlet valve. Naturally, the exact sequence and timing associated with the opening and closing of the valves may vary to optimise operation of the pumping system.

Once the medium has been discharged from the PEC the medium outlet valve and driving fluid inlet valve close and the medium inlet valve and the driving fluid outlet valve open to charge the PEC with medium in the manner described above.

As mentioned above, to be able to operate with a medium containing solid particles, the medium inlet valves are typically cone valves.

The cone valves typically comprise a valve housing defining an elongate cavity, an inlet opening which leads upwardly into the bottom of the cavity and an outlet opening which is in flow communication with a side of the cavity at a position spaced from the inlet opening. A valve seat is provided between the inlet opening and the outlet opening. The valve includes a closure unit and an actuator whereby the closure unit is displaceable between a closed position in which it seats against the valve seat to inhibit the flow of medium through the valve and an open position in which it is clear of the valve seat and permits medium flow through the valve.

<CIT> discloses a process control valve comprising a valve body having an inlet and an outlet and a plug. The plug selectively restricts fluid communication between the inlet and the outlet.

A problem with cone valves is that solid particles from the medium tend to settle in the cavity in the housing above the closure unit which can interfere with the proper functioning of the valve.

It is an object of an embodiment of this invention to provide means which may ameliorate this problem or provide a useful alternative.

This summary is provided to introduce a selection of concepts that are further described in the detailed description below. This summary is not intended to identify indispensable features of the claimed subject matter, nor is it intended for use as an aid in limiting the scope of the claimed subject matter.

In this application ordinal numbers (first, second, third, etc.) are assigned arbitrarily herein, and are used to differentiate between parts, and do not indicate a particular order, sequence, or importance.

Features or steps disclosed as options with respect to one aspect are intended to apply as options to other aspects, except where such combination is not possible.

According to a first aspect of the invention there is provided a valve according to claim <NUM>.

The reduced pressure differential may be the formation of a zone of reduced pressure above the piston that would inhibit closure of the valve. Alternatively, the reduced pressure differential may be the formation of a zone of higher pressure above the piston that would inhibit opening of the valve. Reducing a pressure differential has the advantage of ensuring that the piston can be moved at a desired speed for a given actuator force.

The barrier piston may have any convenient shape; in preferred embodiments, the barrier piston has a cylindrical shape and a circular cross-section, but in other embodiments an oval, rectangular, or polygon cross-section may be used.

Optionally, the valve comprises an actuated valve.

The valve may define a cylindrical chamber having a first end, a second end and a side extending therebetween, the first port opening into the chamber through the first end and the second port leading from the chamber through the side at a position spaced from the first end. The first end may be an operatively bottom end of the chamber. The valve seat may be frusto-conical in shape, tapering inwardly downwardly and the closure unit may be axially displaceable in the chamber between its open and closed positions.

The barrier piston may be mounted for reciprocation in the chamber above the first port. The barrier piston is preferably dimensioned to inhibit the passage of large solid particles into the chamber above the piston, in particular particles which are sufficiently large to potentially interfere with the displacement of the closure unit. To this end, a radial clearance between the piston and an interior surface of the housing defining the side of the chamber may be less than <NUM>. In a preferred embodiment of the invention, the clearance may be approximately <NUM>.

The piston may extend axially beyond the second port (in some embodiments the outlet) thereby effectively closing or blocking the second port when the closure unit is in its closed position to inhibit the backflow of medium through the second port into the chamber above the piston. Inihibiting the flow of solid particles from the second port when the closure unit is in its closed position may comprise inhibiting backflow of solid particles where the second port is the outlet.

Optionally, the one or more bleed passages may be defined in the outer surface of the barrier piston, for example, as axially extending grooves in a radially outer surface of the piston. Hence, a bleed passage will be defined by each of the grooves and the portion of the chamber side which is adjacent the groove.

The valve may include a housing and a sleeve positioned in the housing which defines at least part of the chamber.

In particular, the sleeve may absorb eccentric forces on the piston caused by solids trapped between an engagement surface of the piston and a valve seat (on which the engagement surface abuts) when the piston is being closed. The sleeve may also protect the chamber from high velocity ore particles that would otherwise impact the chamber as the closure unit moves to the closed position and the gap between the closure unit and the valve seat reduces (increasing the particle velocity therethough).

The sleeve may define an opening having a smaller width (or diameter) than the width (or diameter) of the second port. The opening may be vertically offset from the opening such that a portion of the sleeve may act as a protruding wall extending upwards from a lower portion (floor) of the second port. This protruding wall may prevent flow of solid particles at the bottom of the second port (where large particles may settle due to gravity) towards the first port.

Using the sleeve as a liner for the chamber allows the sleeve to be treated with hard-facing to resist wear as it is not a dynamic pressure loaded part.

During use, the medium pressure will deform the housing, which causes the sleeve gap (i.e. the gap between the sleeve and the piston) to reduce and expand as the pressure increases and decreases respectively. The bleed passages connecting the cavity with the second port reduces damage to the sleeve and the piston by allowing the pressure to be relieved, for example, through the axially extending grooves in the piston.

The valve seat, valve, and the sleeve typically wear out by particle erosion over time. A stroke length of the piston and a height of the piston are selected to provide sufficient overlap to cover (or close) the second port.

The central portion may comprise a level (e.g. horizontal, when the valve is mounted with its longitudinal axis in a vertical orientation) surface or a surface having the same slope, or a different slope, to the downward sloping upper surface. The downward sloping upper surface may comprise a conical downward sloping upper surface. The downward sloping upper surface directs any trapped particles in the cavity towards the axially extending grooves in the barrier piston so that small particles flow through the grooves and are guided back to the flow path. The size of particles that can be guided back to the flow path depends on the size of the grooves. In one embodiment, the grooves are <NUM> deep (i.e. extend <NUM> radially inwards towards the longitudinal axis) and <NUM> long; In other embodimemts, the gooves may be between <NUM> and <NUM> deep and extend for the height of the barrier piston.

The downward sloping upper surface of the barrier piston may extend at an angle of at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> degrees to the horizontal.

The downward sloping upper surface of the barrier piston may extend at an angle of less than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> degrees to the horizontal.

Preferred embodiments may have the downward sloping upper surface of the barrier piston extending at an angle between <NUM> and <NUM> degress to the horizontal.

The valve may be in the size range of DN80 to DN500.

According to a second aspect of the invention there is provided a pressure exchange chamber pumping system which includes: at least one pressure exchange chamber; and a medium or pumped fluid valve arrangement in flow communication with the pressure exchange chamber and a driving fluid valve arrangement in flow communication with the pressure exchange chamber at a position longitudinally spaced from the medium valve arrangement, the medium valve arrangement and/or the driving fluid valve arrangement including at least one valve of the type described above.

The medium valve arrangement may include a medium inlet valve whereby medium to be pumped can be admitted into the pressure exchange chamber and a medium outlet valve whereby pumped medium can be discharged from the pressure exchange chamber along a discharge pipe, riser, or the like, at least the medium inlet valve being a valve of the type described above.

In a preferred embodiment of the invention, the pressure exchange chamber pumping system includes a plurality of pressure exchange chambers arranged in parallel, and a feed arrangement including a feeder pump having a suction side and a discharge side connected in flow communication with the medium inlet valves.

The components of the pressure exchange chamber pumping system may be transported in a disassembled or knocked-down kit form for assembly at site.

Hence, according to an unclaimed aspect, there is provided a pressure exchange chamber pumping system kit which includes: pressure exchange chamber defining means defining a plurality of elongate pressure exchange chambers; a plurality of medium valve arrangements each of which is connected or connectable to one of the pressure exchange chambers, each medium valve arrangement including a medium inlet valve whereby medium to be pumped can be admitted into the associated pressure exchange chamber and a medium outlet valve whereby pumped medium can be discharged from the associated pressure exchange chamber; and a plurality of driving fluid valve arrangements which are connected or connectable to the pressure exchange chambers at a position longitudinally spaced from the medium valve arrangements, each driving fluid valve arrangement including a driving fluid inlet valve through which a driving fluid can be admitted into the associated pressure exchange chamber and a driving fluid outlet valve whereby driving fluid can be discharged from the associated pressure exchange chamber, at least one of the valves being a valve of the type described above.

According to an unclaimed aspect there is provided a valve closure unit for use with a valve of the type described above which defines an elongate cavity having a pair of opposed ends and a side extending therebetween, a first opening in flow communication with one end of the cavity, a second opening which is spaced from the first opening and is in flow communication with the cavity, a flow path connecting the first and second openings in flow communication, a valve seat provided in the flow path, the closure unit including (i) a head configured to seat sealingly against the valve seat, and (ii) a barrier piston coupled to the head and defining a bleed passage between the barrier piston and the side, where the barrier piston is receivable in the cavity for reciprocation between a closed position in which the head seats sealingly against the valve seat and an open position in which the head is clear of the valve seat to permit flow through the flow passage.

The valve closure unit may include an annular elastomeric seal. The seal may be held captive between the barrier piston and the head.

The barrier piston may have a circular cylindrical radially outer surface.

The barrier piston may define a bleed passage between an outer surface thereof and the elongate cavity. The bleed passage may comprise an annular gap. Alternatively, or additionaly, the bleed passage may be defined by one or more channels defined in part by one or more longitudinally extending grooves. Each longitudinally extending groove may extend for the entire length of the outer surface of the barrier piston. In a preferred embodiment of the invention, a plurality of circumferentially spaced grooves is provided in the radially outer surface of the barrier piston.

The elongate cavity may be lined by a sleeve.

According to an unclaimed aspect there is provided a method of modifying a pressure exchange chamber pumping system comprising a plurality of pressure exchange chambers, each chamber including (i) a fluid container, (ii) a medium inlet valve whereby medium to be pumped can be admitted into the associated fluid container and (iii) a medium outlet valve whereby pumped medium can be discharged from the associated fluid container, (iv) a driving fluid inlet valve through which a driving fluid can be admitted into the associated fluid container, and (v) a driving fluid outlet valve whereby driving fluid can be discharged from the associated fluid container, which method includes removing at least one valve and replacing it with a valve as described above.

The method may, in particular, include removing each medium inlet valve and replacing it with a valve as described above.

According to an unclaimed aspect there is provided a valve comprising: a first port; a second port which is spaced from the first port; a flow path connecting the first and second ports in flow communication; a valve seat positioned in the flow path; a closure unit which is displaceable between a closed position in which it seats against the valve seat to inhibit the flow of medium through the flow path and an open position in which it permits the flow of medium through the flow path; and a barrier piston configured to inhibit the passage of solid particles which could interfere with the displacement of the closure unit into a closure unit receiving cavity within which at least part of the closure unit is received when the closure unit is in its open position and/or to inhibit the flow of medium from the second port when the closure unit is in its closed position.

These and other aspects of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:.

In <FIG> of the drawings, reference numeral <NUM> refers generally to part of a pressure exchange chamber (PEC) pumping system in accordance with an embodiment of the invention.

The PEC pumping system <NUM> includes three PECs <NUM>, <NUM>, <NUM> defined by lengths of pipe <NUM>, <NUM>, <NUM>, each having a medium or pumped fluid valve arrangement <NUM>, <NUM>, <NUM> connected respectively thereto at one end thereof, and a driving fluid valve arrangement <NUM>, <NUM>, <NUM> connected respectively thereto at the other end thereof, i.e. longitudinally spaced from the medium valve arrangements <NUM>, <NUM>, <NUM>, in this embodiment. However, in other embodiments, different configurations of PEC may be used (such as a loop) so that the medium valve arrangements <NUM>, <NUM>, <NUM> may be located near the driving fluid valve arrangements <NUM>, <NUM>, <NUM>.

Each medium valve arrangement <NUM>, <NUM>, <NUM> includes a medium inlet valve <NUM>, <NUM>, <NUM>, in accordance with an embodiment the invention and as described in more detail herebelow, whereby medium to be pumped can be admitted into the associated pipe <NUM>, <NUM>, <NUM> and a medium outlet valve <NUM>, <NUM>, <NUM> whereby pumped medium can be discharged from the pipe <NUM>, <NUM>, <NUM> along a discharge riser <NUM>. Similarly, each driving fluid valve arrangement <NUM>, <NUM>, <NUM> includes an inlet valve <NUM>, <NUM>, <NUM> through which a driving fluid can be admitted into the associated pipe and an outlet valve <NUM>, <NUM>, <NUM> whereby driving fluid can be discharged from the associated pipe.

The PEC pumping system <NUM> further includes a feed arrangement, part of which is generally indicated by reference numeral <NUM>, configured to feed medium to be pumped to the medium inlet valves <NUM>, <NUM>, <NUM> as described in more detail herebelow. The feed arrangement <NUM> includes a feed or delivery pump (not shown in detail). The feed arrangement <NUM> further includes a pipe <NUM> which is connected to a source of ore particles and three feed lines <NUM>, <NUM>, <NUM> each of which has an upstream end connected to the pipe <NUM> and a downstream end. The downstream ends of the feed lines <NUM>, <NUM>, <NUM> are connected, respectively, to the medium inlet valves <NUM>, <NUM>, <NUM>. Hence, in use medium to be pumped is transported through the pipe <NUM> and the feed lines <NUM>, <NUM>, <NUM> to the medium inlet valves <NUM>, <NUM>, <NUM>.

In use, with the medium inlet valve <NUM>, <NUM>, <NUM>,<NUM> open and the corresponding driving fluid outlet valve <NUM>, <NUM>, <NUM> open, medium enters the associated pipe <NUM>, <NUM>, <NUM> and displaces the driving fluid out of the associated driving fluid outlet valve <NUM>, <NUM>, <NUM>. When a desired quantity of medium has entered the pipe <NUM>, <NUM>, <NUM>, the medium inlet valve <NUM> and driving fluid outlet valve <NUM> are closed. The medium outlet valve <NUM>, <NUM>, <NUM> and the driving fluid inlet valve <NUM>, <NUM>, <NUM> are opened such that driving fluid enters the pipe at high pressure and displaces the medium through the respective medium outlet valve <NUM>, <NUM>, <NUM> and thereby out of the pipe <NUM>, <NUM>, <NUM> and into the discharge riser <NUM>.

Once the medium has been discharged from the pipe <NUM>, <NUM>, <NUM>, the associated medium outlet valve and driving fluid inlet valve are closed and the medium inlet valve and driving fluid outlet valve are opened, once again, to charge the pipe <NUM>, <NUM>, <NUM> with medium in the manner described above.

To permit more or less continuous pumping, the operation of the valves of the different PECs <NUM>, <NUM>, <NUM> is staggered such that the filling of the pipes <NUM>, <NUM>, <NUM> with medium and the discharge of medium occurs in a more or less continuous basis.

The medium inlet valve <NUM>, <NUM>, <NUM>,<NUM> are substantially identical. In the interests of brevity of description, only the medium inlet valve <NUM> is described in detail herebelow with reference to <FIG> of the drawings.

The valve <NUM> includes a hollow housing <NUM> which partially defines a cylindrical chamber <NUM> having a circular cross section, and a cap <NUM> above the housing <NUM>. The chamber <NUM> is defined by a bottom <NUM>, a top <NUM> and a side <NUM> extending between the bottom <NUM> and the top <NUM>. The top <NUM> is defined by a lower surface of the cap <NUM>. A circular cylindrical sleeve or liner <NUM> is positioned in the housing and a radially inner surface of the liner <NUM> abuts the side <NUM> and extends into the cap <NUM>. A first port <NUM> extends through the housing <NUM> into the bottom <NUM> of the chamber <NUM>. A second port <NUM> extends through the housing <NUM> and liner <NUM> into the chamber <NUM> through the side <NUM> at a position spaced from the port <NUM>. In this embodiment, the port <NUM> forms an inlet and the port <NUM> forms an outlet. However, in other embodiments the port <NUM> could be an inlet and the port <NUM> an outlet.

An annular seat ring <NUM> is mounted in the chamber <NUM> adjacent to the inlet <NUM>. In the embodiment shown, the sleeve or liner <NUM> extends between the seat ring <NUM> and into the cap <NUM>. An opening <NUM> is provided in the liner <NUM> and is aligned with the port <NUM>. The ports <NUM>, <NUM> are connected in flow communication by means of a flow path, part of which is formed by a passage <NUM> (see <FIG>) extending through the seat ring <NUM>. The passage <NUM> includes a cylindrical portion <NUM> (having a circular cross section) (<FIG>) which is in flow communication with the port <NUM> and a frustoconical portion <NUM> (<FIG>) which opens into the chamber <NUM>. A surface <NUM> of the frustoconical portion <NUM> forms a valve seat as described in more detail herebelow.

The valve <NUM> further includes a closure unit, generally indicated by reference numeral <NUM> and an actuator, part of which is generally indicated by reference numeral <NUM>.

The valve <NUM> extends along a longitudinal axis <NUM> which is co-axial with the circular cylindrical chamber <NUM>, the inlet port <NUM>, and the liner <NUM>; and perpendicular to the outlet port <NUM>. In this embodimeint, the valve <NUM> is oriented generally vertically (i.e. longitudinal axis <NUM> is vertical), with the first port <NUM> lower than the second port <NUM>.

The closure unit <NUM> includes: (i) an annular seal <NUM> which is typically formed from an elastomeric material and has a frustoconical seal surface <NUM> which is complementary to the valve seat <NUM>, (ii) a head <NUM>, and (iii) a barrier piston <NUM>.

The seal <NUM> is sandwiched between the head <NUM> and the barrier piston <NUM> which are secured together by a retaining stud bolt <NUM> which extends axially through the head <NUM> and piston <NUM> and retaining nuts <NUM> which are mounted on end portions of the stud bolt <NUM> to urge the head <NUM> and piston <NUM> inwardly towards one another and retain the seal <NUM> in position. The stud bolt <NUM> and retaining nut <NUM> may also be considered as part of the closure unit <NUM>, although different techniques for mutually coupling the seal <NUM>, head <NUM>, and barrier piston <NUM> may be used in other closure units.

The head <NUM> defines a frustoconical surface <NUM> which is complementary to the valve seat <NUM>.

The barrier piston <NUM> has a circular cylindrical outer surface <NUM>, the dimensions of which are selected such that it is snuggly receivable for reciprocation within the sleeve <NUM> with little clearance between the outer surface <NUM> of the piston <NUM> and a radially inner surface <NUM> of the sleeve <NUM>. In some embodiments, the little clearance may comprise an annular gap that functions as a bleed passage.

The actuator is typically in the form of a linear actuator such as a hydraulic piston and cylinder arrangement which includes an elongate coaxially extending actuator rod <NUM> which extends through the cap <NUM> at the top of the housing <NUM> and is connected to the stud bolt <NUM> to facilitate displacement of the closure unit <NUM> and piston <NUM> between a closed position (shown in <FIG> of the drawings) and an open position (shown in <FIG> of the drawings).

As can best be seen in <FIG> of the drawings, a plurality of circumferentially spaced axially extending grooves <NUM> is provided in the radially outer surface <NUM> of the piston <NUM> which, together with the radially inner surface <NUM> of the sleeve <NUM> (or the side <NUM> for embodiments where a sleeve is not used) form bleed passages to prevent the creation of a vacuum as described in more detail below. Furthermore, the grooves <NUM> allow fine particles to settle out of the cavity <NUM> and towards the second port <NUM>, thereby preventing blockages in the cavity <NUM>. The grooves <NUM> also assist with reducing the viscous forces during movement of the piston <NUM>.

The barrier piston <NUM> defines an upper portion <NUM> having a flat central portion <NUM> defining a bore <NUM> for receiving the actuator rod <NUM>, and an outer portion <NUM> sloping downwards (in this embodiment towards the valve seat <NUM>) as it extends towards the radially outer surface <NUM>. The outer portion <NUM> may be referred to as a downwards sloping portion when the valve is mounted in an upright orientation, as shown in <FIG> and <FIG>. In this embodiment, the downwards sloping portion <NUM> extends at an angle of between <NUM> and <NUM> degrees to the horizontal (i.e. perpendicular to longitudinal axis <NUM>).

As mentioned above, the medium typically comprises a liquid (such as water) in which solid particles are entrained. Some of the solid particles may be small (fine), others medium size, and others relatively large.

With reference to <FIG> of the drawings, in the closed position of the valve <NUM>, the seal surface <NUM> and the frusto-conical surface <NUM> of the head <NUM> abut sealingly against the valve seat <NUM> formed by the frusto-conical portion <NUM> of the seat ring <NUM> to inhibit the flow of medium through the valve. In this regard, the seal <NUM> protrudes radially beyond the surface <NUM> such that when the closure unit <NUM> is being displaced towards its closed position, the seal surface <NUM> of the seal <NUM> abuts against the valve seat <NUM> before the frusto-conical surface <NUM>. By virtue of the seal <NUM> being formed of an elastomeric material, it is able to form a reliable seal even if small solid particles are trapped between the surface <NUM> and the valve seat <NUM>.

Of importance to note is that in the closed position, the piston <NUM> protrudes axially into the chamber <NUM> from a position, below a lower edge of the opening <NUM> upwardly beyond the port <NUM> and opening <NUM> and accordingly forms a barrier which effectively closes off the opening <NUM> and resists the flow of material or medium through the port <NUM> into the chamber <NUM> even when the valve is in its closed position. The portion of the chamber <NUM> above the piston <NUM> forms a closure unit receiving cavity, generally indicated by reference numeral <NUM>, into which at least part of the closure unit <NUM> (e.g. the piston <NUM>) is displaced when the valve is in an open position as described below.

With reference to <FIG> of the drawings, to open the valve <NUM>, the rod <NUM> is displaced in the direction of arrow <NUM> such that the piston <NUM> and closure unit <NUM> are drawn upwardly into the portion of the chamber <NUM> defining the closure unit receiving cavity <NUM> thereby connecting the inlet <NUM> and outlet <NUM> in flow communication and permitting the free flow of medium through the valve <NUM>.

To close the valve <NUM>, the piston <NUM> and closure unit <NUM> are displaced in the direction opposite to the direction of arrow <NUM> into the closed position shown in <FIG> of the drawings.

By virtue of the snug fit of the piston <NUM> within the chamber <NUM> and in particular the restricted clearance between the radially outer surface <NUM> of the piston <NUM> and the inner surface <NUM> of the liner <NUM>, large solid particles are unable to pass between the piston <NUM> and the liner <NUM> into the portion of the cavity above the piston <NUM> where they could potentially accumulate and inhibit the displacement of the piston <NUM> and the closure unit <NUM> to its open position.

The provision of the grooves <NUM> permit limited flow of medium into the chamber <NUM> above the piston <NUM> (the closure unit receiving cavity <NUM>) when the piston <NUM> and closure unit <NUM> are being displaced towards the closed position and limited flow of medium out of the closure unit receiving cavity <NUM> when the piston <NUM> and closure unit <NUM> are being displaced towards the open position. This avoids any significant pressure differential between the closure unit receiving cavity <NUM> and the second port <NUM>. Without this pressure balancing, a zone of reduced pressure could be created above the piston <NUM> which could resist displacement of the closure unit <NUM> towards its closed position. Similarly, a zone of increased pressure could be created above the piston <NUM> which could resist displacement of the closure unit <NUM> towards its open position. The dimensions of the grooves are selected to inhibit the passage of large solid particles therethrough. In this embodiment, each groove <NUM> has a width of <NUM> and a maximum depth of about <NUM>. The number and depth of grooves required may increase for larger diameters of barrier piston. In another embodiment of the invention, if desired, grooves could instead or in addition be provided in the radially inner surface <NUM> of the liner <NUM>, and may have any convenient cross-sectional shape or configuration.

The barrier piston <NUM>, head <NUM>, seal <NUM>, stud bolt <NUM>, and nut <NUM>, together may form a valve closure unit which could be replaced as a unit should the seal <NUM> or one of the other parts become worn or fail. Similarly, the liner <NUM> and the seat ring <NUM> could be replaceable wear items. The wear parts such as the valve seat ring <NUM>, valve head <NUM>, barrier piston <NUM>, liner <NUM>, valve seal <NUM> are easy to replace by removing a top-cover (not shown) and unscrewing the retaining nut <NUM>.

The valve <NUM> will be particularly suitable for use in an environment where the medium contains solid particles such as in the pressure exchange chamber pumping system and will provide reliable operation thereof.

Reference is now made to <FIG>, which is a partial sectional view of a valve <NUM> according to another embodiment of the present invention. Valve <NUM> is almost identical to valve <NUM>, however valve <NUM> has a sleeve (or liner) <NUM> (instead of sleeve <NUM>) defining an opening <NUM> that has a smaller diameter than the diameter of the second port <NUM>. The opening <NUM> is vertically offset from the opening <NUM> such that a portion of the sleeve <NUM> acts as a protruding wall <NUM> extending upwards from a lower portion (floor) of the second port <NUM>. This protruding wall <NUM> prevents flow of solid particles at the bottom of the second port <NUM> (where large particles may settle due to gravity) towards the first port <NUM>. When the the second port <NUM> is the outlet, this prevents backflow towards the first port (the inlet) <NUM>.

Although the valve has been described with particular reference to its application as a medium inlet valve in a pressure exchange chamber pumping system, it will be appreciated that it would be suitable for use in many other applications. In particular, it could be used as a medium outlet valve, a driving fluid inlet valve and/or a driving fluid outlet valve. Indeed, a valve in accordance with the invention could be used in applications other than PEC's.

Claim 1:
A valve (<NUM> or <NUM>) comprising:
a housing (<NUM>) defining a cylindrical chamber (<NUM>) having a central axis (<NUM>);
a first port (<NUM>);
a second port (<NUM>) which is spaced from the first port (<NUM>);
a sleeve (<NUM> or <NUM>) concentrically mounted within the housing cylinder (<NUM>);
a flow path connecting the first port (<NUM>) and the second port (<NUM>) in flow communication to allow medium containing solid particles to pass therethrough;
a valve seat (<NUM>) positioned in the flow path;
a closure unit (<NUM>) which is displaceable between a closed position in which it seats against the valve seat (<NUM>) to inhibit the flow of medium through the flow path and an open position in which it permits the flow of medium through the flow path;
a cavity (<NUM>) configured to receive at least part of the closure unit (<NUM>);
wherein the closure unit (<NUM>) further comprises (i) a barrier piston (<NUM>) configured to inhibit the flow of solid particles from the second port (<NUM>) when the closure unit (<NUM>) is in its closed position and thereby inhibit the passage of such solid particles into the cavity (<NUM>); (ii) one or more bleed passages connecting the cavity (<NUM>) with the second port (<NUM>) in flow communication to provide a pressure balancing arrangement that reduces a pressure differential therebetween, and (iii) a downwards sloping top (<NUM>) extending from a central portion (<NUM>) of the barrier piston (<NUM>) to an outer surface (<NUM>) of the barrier piston (<NUM>) to permit fine particles in the cavity (<NUM>) to settle through the one or more bleed passages towards the second port (<NUM>);
characterised in that the sleeve (<NUM> or <NUM>) defines a bore transverse to the central axis (<NUM>) of the sleeve (<NUM> or <NUM>) so that the second port (<NUM>) extends through the housing (<NUM>) and sleeve (<NUM> or <NUM>) into the chamber (<NUM>) through a side (<NUM>) of the sleeve, and
wherein the sleeve (<NUM> or <NUM>) surrounds the barrier piston (<NUM>) with clearance between the outer surface (<NUM>) of the barrier piston (<NUM>) and a radially inner surface (<NUM>) of the sleeve (<NUM> or <NUM>) so that the sleeve (<NUM> or <NUM>) and housing (<NUM>) provide support to the barrier piston (<NUM>) to reduce or prevent lateral movement that may arise when ore particles are trapped between part of the closure unit (<NUM>) and the valve seat (<NUM>).