Field of the invention

The present invention relates to cleaning apparatus and methods for cleaning screens used in vibratory screening apparatus, especially screens used in solids and liquids separations such as occur during drilling operations carried out in the oil and gas industry.

Background to the Invention

Screening equipment, especially vibratory screening equipment is widely used in drilling operations to separate solids from liquids, in particular to separate solids out from used drilling mud to allow its reuse. Solids such as drill cuttings are generally removed as far as practicable. Deliberately introduced solids may also be removed. In a drilling mud composition, weighting agents, lost circulation material, or sized solids provided to minimise damage of a formation during drilling, can be present. These solids may be selected by using appropriate screen mesh sizes and recycled back into the screened drilling mud.

Vibratory screening equipment such as shale shakers and mud cleaners are used for these duties. They employ one or more, often several, screens of differing mesh sizes to achieve the required solids and liquids separation. The finer mesh sizes of screens can become blinded, blocked with a layer of solids which can be difficult to remove. This is especially so if particles present in the feed to a screen are of a size comparable to that of the apertures in the mesh. Such particles can become stuck in the mesh and not readily dislodged by the vibratory action applied to the screen. Even if a mesh is only partially blinded it can have a detrimental effect on the classification efficiency of a screen. A screen of a given mesh size will allow particles below the size of its apertures to pass through, therefore screen meshes can be chosen to classify particles i.e. separate them on the basis of size. Where solids builds up on a blocked or partially blocked screen then particles that could pass through the screen may not do so as they do not penetrate the solids layer building up on the screen. Thus the intended separation may not be achieved.

Cleaning is also carried out to prevent solids/drilling fluids drying out on screens when operations are interrupted or finished. Good cleaning is also required when a screen is to be repaired. For these reasons there is a need for frequent screen cleaning during many drilling operations. Typically cleaning of screens is carried out with a hand held high pressure hose spray. Cleaning fluids used include water, water and cleaning agents, or a non aqueous fluid such as base oil (petroleum fractions) i.e. a hydrocarbon based cleaning fluid.

However this results in the spreading of solids, cleaning fluid and components of used drilling mud around the local environment, which may be hazardous and/or environmentally unacceptable. This can include spray droplets of cleaning fluid and components of used drilling mud dispersing in the atmosphere that create a breathing hazard.

With shale shakers being constructed with increasing numbers of screen decks and making use of finer screens there is a need for apparatus and methods for efficient claiming of screen, especially in the demanding environment of offshore drilling.

Description of the Invention

According to a first aspect, the present invention provides an apparatus for cleaning screen panels comprising:

an enclosure including a screen loading zone and a screen washing zone in communication with the screen loading zone;

at least one screen carriage formed and arranged for mounting at least one screen panel thereon and for transporting a said screen panel, edge first, into the screen washing zone and reversing to return a said screen panel to the screen loading zone;

wherein the screen washing zone has screen washing jets mounted for washing both faces of a screen panel mounted on the carriage. The screen carriage transports a screen panel edge first into and then back out of the screen washing zone i.e. the carriage is arranged so that the screen panel is mounted with its principal faces generally facing transverse to the direction of travel of the carriage. Screen panels may be formed in a number of different ways to provide an area of screening surface to separate out solids of above a certain size. The screening panel will have two sides, they can be described as a "top side" and an "underside" when the screening panels are used in a more or less horizontal orientation. The term face when applied to screen panels described herein refers to the surface on one side or the other of the panel. Thus the term "both faces" refers to both sides, such as the top side and the underside of the screening panel.

The term principal face refers to the general orientation of a side of a screen panel, as a screening panel may, for example, comprise areas of screening surface at different angles to each other in a zig-zag arrangement where a portion of the area of a surface faces in a different direction to an adjacent area of the surface. The principal face refers to the general orientation of the whole surface of the panel. A screen carriage may be formed and arranged to mount more than one screen panel in the same manner. The two or more screen panels are mounted on the carriage so that the faces of one panel do not obscure another from the washing jets i.e. the panels are mounted so that their faces do not overlap. The edge first transportation of the screen panels allows compact arrangements when more than one carriage is provided as described and illustrated hereafter with reference to specific embodiments.

The screen panels mounted on a carriage are cleaned by screen washing jets when in the screen washing zone. This may be achieved by mounting screen washing jets that are formed to wash (spray) all of both faces of a screen panel when it is in the washing zone. In such an arrangement the carriage may be held stationary when in the screen washing zone. Alternatively screen washing jets may be formed to move so as to provide progressive washing of both faces of the screen panel. The washing jets move so that their spray pattern covers the whole of the surface area of both faces of the screen panel.

However, it is preferred that the screen washing jets are formed and arranged for washing both faces of a screen panel mounted on the carriage as it moves into and/or as it moves out of the screen washing zone. Such an arrangement is compact, requires fewer washing jets, can avoid the complication of providing moving washing jets and can provide effective cleaning methods. The screen washing jets are mounted for cleaning both faces of screen panels on the carriage as it moves into the screen washing zone. High pressure (e.g. 100 to 200 bar) low volume jets are typically employed to give good cleaning and to minimise the quantity of fluid required to clean a screen panel. By washing the screen panel as it is in motion, fewer wash jets are required as they need only wash the whole height or width of screen panel faces that are passing by to achieve good cleaning. They do not need to simultaneously spray the whole surface area of the faces or to move in order to spray the whole area of the faces. However the screen washing zone may be provided with additional wash jets, for example lower pressure screen rinsing jets that can be used to remove residual contamination. Such processes may be carried out with the screen panel in motion or held stationary within the washing zone. The screen washing jets are supplied with cleaning fluid from a high pressure supply, e.g. from a pump system.

Conveniently screen panels are washed by the screen washing jets both as the carriage moves into the screen washing zone and also as it moves out of the screen washing zone. Thus in one cycle, into and back out of the washing zone, both faces of a screen panel can be washed twice.

Conveniently the screen washing jets are mounted proximal to the entrance of the screen washing zone. Typically jets are arranged on opposite walls of the enclosure in the screen washing zone to direct washing fluid directly onto both faces of screen panels mounted on a carriage as it enters the screen washing zone. The jets may be arranged to direct their spray at or substantially at right angles to the direction of travel of the carriage, so as to maximise the force of the sprayed fluid acting on the screen panel. Spray jets may be designed to produce a desired spray pattern in the usual way, for example in a fan or conical shape to project fluid in the desired pattern at the screen panels. The expression "to direct their spray at or substantially at right angles to the direction of travel of the carriage" refers to the principal direction of washing fluid emitted from the jets i.e. the centre axis line of a cone or fan spray pattern is the principal direction of the washing fluid.

Conveniently, to aid in washing solids away from the faces of the screen panel the jets may be angled slightly away from the right angle (principal direction of spray normal to the direction of carriage travel). For example the principal direction of their spray may be angled up to say 20 ^s , typically around 5 to 10 ^s from right angles. Typically the angle will be in the direction away from the loading zone so as to reduce the amount of spray rebounding from the screen panels that may go back towards the screen loading zone.

A plurality of washing jets may be provided at both sides of the screen panel to ensure the whole of the portion of screen panel passing the location of the screen wash jets receives a powerful washing action. The screen washing action may be enhanced to some extent by providing jets which are directly opposed i.e. the spray of cleaning fluid is directed to opposite sides of the same portion of screen panel at the same time, creating turbulence which may aid in dislodging particles of solid trapped in screen mesh, including by causing the mesh to flex in different directions.

As an alternative the screen washing jets may be set so as to not be directly opposed but the screen washing jets are formed and arranged so that the spray or sprays of cleaning fluid washing a portion of one face of a screen panel are offset from the spray or sprays of cleaning fluid washing the other face of the screen panel as it passes into and/or out of the screen washing zone. This arrangement of offset washing jets can have advantages. As a given portion of screen panel receives the force of a spray or sprays of cleaning fluid from only or substantially from only, one side at a time, the cleaning action can include pushing particles lodged in a screen mesh (blinding of the screen mesh) out of the mesh without the force of the jet spray(s) acting on the other face of the screen panel acting in the opposite direction.

The screen loading zone may be provided with rinsing jets for rinsing a screen panel with fluid before and/or after it has been in the screen washing zone. The apparatus may be provided with two or more screen carriages. Operations can be arranged to carry out sequential transportation of screens into and back out of the screen washing zone.

The carriages may be mounted one carriage adjacent the next, transverse to the direction of travel into and out of the screen washing zone. Screens mounted on each carriage are washed on both faces as a respective carriage moves into and/or as moves out of the screen washing zone. The next carriage then follows suit and so on until all the carriages have taken screens mounted thereon through the cleaning procedure. If desired or required the cleaning procedure may include more than one cycle into and out of the screen washing zone for each carriage and screen panels loaded thereon. Such repeated cycling may be carried out on each carriage before the next carriage is employed or all the carriages may be cycled into and out of the washing zone before repeat cycles operate. Where a plurality of carriages are provided in an apparatus then additional washing jets may be provided, for example so that each carriage has a set of washing jets at either side of and equidistant, or approximately equidistant from screen panels entering the screen washing zone. However it has been found that additional sets of jets may not be required. Jets placed at opposite sides of the enclosure can be sufficient even where a plurality of carriages is provided.

The apparatus is typically provided with a sump for collecting washing fluid and solids dislodged from the screens. The sump may be emptied by gravity or by a pump. The sump may be a holding tank for holding washings from multiple wash cycles.

The used cleaning fluid may be subject to filtration procedures to separate solids from liquid to facilitate disposal and/or reuse. For example the used cleaning fluid may be directed from a sump to a screening apparatus which removes solids for disposal and allows recycle of the cleaning fluid.

Conveniently the sump may be fitted with sump washing jets, to assist in cleaning of solids from the sump. These may be fed with the same washing fluid as used in the screen washing jets. Advantageously the screen loading zone is accessed by means of a door (e.g. a lid on the top of the enclosure) that is closed after loading screen panels. The enclosure can contain all or substantially all of the cleaning fluid and solids washed off the screen panels and direct fluid and solids to the sump for disposal, reprocessing and/or recycle. The door or lid may be provided with appropriate safety interlocks (safety switches or buttons) to prevent inadvertent operation of the sprays and motion of the carriage(s) during loading and unloading operations. The interlocks will also halt spraying and operation of carriages if the door or is opened during a cleaning procedure.

Where hazardous or harmful vapour or gas may be present, from the dirty screen panels or the cleaning fluid selected, then the apparatus may be fitted with appropriate systems to control the risk. For example the apparatus may be fitted with an air extraction system on the enclosure, with an air inlet provided to replace the extracted air. The air inlet may be provided with a noise reduction system such as a panel of air permeable sound reducing material.

The screening fluid may be supplied at high pressure/low volume to the screen washing jets and a lower pressure to the screen rinsing jets. A pump is employed to provide the desired pressures. The carriages may be powered by pneumatic or hydraulic pistons, avoiding the need for electrical equipment within the enclosure, to reduce risk of loss of power due to water damage and reduce risk of fire/explosion.

For example the carriages may have a base on which loaded screen panels may rest. The base or another part of the carriage is connected directly (or indirectly via a shoe as described below) to a pneumatic piston that may conveniently be located below the base, where the carriages travel horizontally into and out of the washing zone. The extension and retraction of the piston provides the reciprocating motion to the carriage. In a particularly convenient arrangement the base of a carriage is connected to a shoe sitting on and preferably straddling or even wrapping round a rail running from the screen loading zone into the screen washing zone. The shoe running along the rail constrains the direction of travel of the carriage. The shoe may be connected to a pneumatic piston arrangement that is fitted inside the rail to provide a particularly compact arrangement as described hereafter and with reference to a particular embodiment. Suitable arrangements of cylinders and shoes are commercially available, for example so called "Rodless Cylinders" from Pneumax UK Ltd of Southampton, United Kingdom. These arrangements have a double headed piston running in a cylinder that is the inside of a rail on which the shoe rides. The shoe is connected to the piston inside the rail with more or less gas tight sealing provided along the length of the rail by means of a band sealing system. Air pressure applied at one side of the piston pushes it along the cylinder carrying the shoe with it. Conveniently where the carriage runs horizontally along a rail of this type the shoe wraps round the rail and the connection to the piston, contained in the cylinder within the rail, is through a slot underneath the rail. This arrangement aids in prevention of entry of solids and fluid to the piston and cylinder mechanism.

Alternatives can include electrically driven carriages (e.g. a rack driven by a pinion powered by an electric motor) or even manual operation e.g. the carriage has a handle projecting out of a slot in the enclosure, to allow an operator to move the carriage back and forth.

Carriages may also ride on rollers or on an endless belt or chain arrangement. However the use of pneumatic or hydraulic pistons and guide rails has advantages of relative simplicity and strength.

The carriages are sized to suit the dimensions of screen panels to be cleaned. The carriages may be made sufficiently large to fit a variety of different screen panel sizes. During the cleaning process the screen panels may be subject to significant forces applied by the washing fluid. The carriages are generally formed and arranged to support screen panels upright and with their principal faces facing substantially normal to the direction of travel ("edge first" travel). More generally any type of screen panel may be supported in a suitably configured carriage. Carriages are generally configured to support screen panels in a vertical or substantially vertical orientation so that solids dislodged from both faces during washing can easily fall off the faces under gravity. For example, where the screen panels are self supporting, (or fixed to a support frame even when removed from a shale shaker or other screening apparatus), then the carriage may employ a base, such as an elongate member (that may be a plate, a bar, or a hollow box section tube) on which an edge of the screen panel and/or any associated support frame can rest. It will be understood that self supporting in this context refers simply to a screen panel (or screen panel and attached support frame) that is sufficiently stiff to support its own weight when stood on an edge and to withstand washer jet pressure without deforming substantially.

The carriage is arranged to prevent the panel falling flat or otherwise moving substantially during the washing procedure. The panel may be held upstanding by support members, typically upstanding support members; conveniently upstanding carriage ends positioned one at either end of the base. The support members may engage edges of the screen panel to avoid obscuring the faces to be washed. The support members keep the screen panel upright or at another selected orientation during washing and transport into and out of the washing zone.

The engagement of screen panel edges may be by providing support members (e.g. carriage ends) that include or are formed as elongate slots or pairs of rails into which edges of the screen panel and/or support frame fit. Alternatively hook or fork features may be provided on the support members that fit about edges of the screen panel (and/or associated support frame if present) to prevent excessive lateral movement during washing. Similar arrangements may be used on the carriage base if desired to provide support against lateral movement. Releasable fastenings such as clamps may be employed but this will increase the time required to load screen panels into the apparatus.

An example of a self supporting screen panel would be a screen panel of a mesh or meshes bonded to an apertured support plate. Such panels are generally clamped to a support frame for use in vibratory screening machines and are widely used on shale shakers. Examples are described in WO 03/013690 (Axiom Process Limited). If the screen panel is not self supporting, for example if it is or is largely an unsupported mesh of a material that will collapse under its own weight when stood on edge, then the carriage ends can be fitted with hooks or clamps to engage the mesh or fittings such as hooks that may be at the periphery of the mesh. The carriage may even include a frame for attaching and bracing an unsupported mesh if desired. Alternatively a not self supporting screen panel may be loaded into the apparatus whilst supported on a support frame such as one it is supported by when in use for screening procedures.

Conveniently the screen loading zone is horizontally adjacent to the screen washing zone and the carriage or carriages travel substantially horizontally from the loading zone into and back out of the washing zone. Screens are held substantially vertically on the screen carriages with faces facing substantially normal to the direction of travel of the carriage. The loading zone is conveniently provided with a door that is a lid (e.g. a hinged lid) on its top to provide access for loading and unloading screens.

Alternatively the screen loading zone may be vertically above the screen washing zone, providing a more compact footprint to the apparatus, but with greater height required. The carriages descend from the screen loading zone down into and then back up out of the screen washing zone. In such an arrangement a sump if provided is below the bottom of the screen washing zone. Access to the screen loading zone may be by a lid on the top of the enclosure or by a door on a side of the enclosure, at the screen loading zone. Where a side entry door is employed the carriages may conveniently include a base, an upright support member distal from the loading entrance, at the back of the loading zone, and a top support member connected to the upright support member and spaced above the base. Screen panels are then loaded onto the base and held upright by appropriate fittings on the top support member and/or the upright support member and/or the base.

To aid in keeping as much wash fluid and displaced solids as possible in the screen washing zone especially, but not only, where more than one carriage is fitted, the periphery of the entrance between it and the screen loading zone may have screening (shuttering). Alternatively or additionally shuttering may be provided on the carriages.

Where the carriages travel horizontally, upright ends of carriages, especially those proximal to the entrance to the screen washing zone, when the carriage is located in the loading zone, may be provided with shuttering transverse to the direction of travel so as to tend to keep splashing from the washing jets within the washing zone. Thus for example when three carriages are employed and one is in the washing zone, the other two may have shutters at their ends, proximal to the entrance of the washing zone, keeping the bulk of splashing that may occur from the cleaning process within the washing zone. Stray solids sprayed back into the screen loading zone may conveniently be washed away by use of rinsing jets as discussed above. Similarly, where carriages travel down into and then up out of the washing zone then the base of a carriage may be fitted with shuttering and/or a top support member may be fitted with shuttering. A yet further advantageous option in this respect is the provision of shuttering between the locations of carriages, in the loading zone. The shuttering divides the loading zone, into compartments. Washing fluid and solids that come out into the loading zone as a screen panel on a particular carriage is washed are constrained from contaminating adjacent or even further away carriages and their load of screen panels. Thus the loading zone may be provided with shuttering in the form of panels, lateral dividers, one between each pair of carriages, in the direction of travel of the carriages. For example if three carriages are provided the loading zone will have two dividing panels to divide the zone into three compartments, one for each carriage. Conveniently the operation of an apparatus of the invention and the control of services that may be employed such as compressed air, washing fluid, electricity and hydraulic fluid is by means of an appropriate control panel that can include appropriate processing logic e.g. from a microprocessor, to carry out a cleaning procedure automatically, once a screen panel or screen panels has been loaded into an apparatus of the invention. Thus for example a screen cleaning system may comprise: an apparatus for cleaning screen panels as described herein; a controller; a compressor to supply compressed air for pneumatic operation of a carriage or carriages, a pump to pressurise cleaning fluid from a supply of the same to feed washing (and optionally rinsing) jets; and optionally a sump pump for emptying a sump fitted to the apparatus. Where alternative means are employed, such as electricity or hydraulics are used to drive carriages, then appropriate components are substituted in the system as appropriate.

According to a second aspect the present invention provides a method of cleaning a screen panel comprising: providing an apparatus of the invention as described herein; loading a screen panel onto a screen carriage of the apparatus positioned in the screen loading zone; transporting the screen panel into and then back out of the screen washing zone; and operating screen washing jets in the screen washing zone to wash both faces of the screen panel with a cleaning fluid. Preferably the screen panel is washed by screen washing jets a as it moves into and/or as it moves out of the screen washing zone.

The method of the second aspect may include use of any or all of the optional features of an apparatus of the invention as described herein.

The method of the second aspect of the invention, making use of the apparatus of the first aspect of invention has been found capable of effective washing of screen panels without the need for scrubbing with brushes or other additional agitation or vibration being applied to the screens.

Suitable fluid for washing screen panels depends on the circumstances but is typically water, water with added cleaning agents such as detergents, or a non-aqueous cleaning fluid such as base oil (petroleum fractions).

The apparatus of the present invention may incorporate additional features including for example a screen loading system where one or more screen panels are loaded, in the loading zone, onto a storage rack. A screen carriage receives a screen panel from the rack and takes it through the screen washing procedure. The cleaned screen may then be returned to the storage rack. Typically the screen loading rack is formed to mount a plurality of screen panels. The screen carriage may return the cleaned screen panel to the rack before receiving another screen panel for washing. This storage rack and screen panel system can be formed in various ways. For example the storage rack may be in the form of a rotating carousel from which a screen carriage picks up a screen panel when at a pick up location and may return it to the same place after cleaning. The carousel then rotates to position the next screen panel at the pick up location for picking up and cleaning. The screen panel may be picked up by a suitable mechanism on the carriage or even by a separate robotic arm. As an alternative to returning the cleaned screen panel to the storage rack it may be delivered by the carriage to a second storage rack, for cleaned screen panels. The second storage rack may be provided within or in communication with the screen loading zone. Conveniently the apparatus may incorporate a screen drying module that dries washed screens before storage. The screen drying module may take the form of an enclosure within or in communication with the screen loading zone which includes drying means such as a forced warm air supply to dry screens after washing. Thus the method of cleaning screen panels may include the step of drying making use of the drying module.

Conveniently the apparatus incorporates a finishing jet system to spray the cleaned screen panels with a preservative fluid. The preservative fluid protects the screen panel from corrosion during storage, before subsequent reuse in screening operations. Examples of such fluid would be a water repellent light oil, a grease or a wax that may be dispersed in a solvent. The finishing jet system may be located for example either in the screen washing zone, the screen loading zone or in a separate finishing module that may be in communication with the screen loading zone.

Conveniently the apparatus may be fitted with an automated screen packing system. The screen packing system places cleaned screen panels into protective packing that is suitable for storage or transport to an alternative location. For example a location in the screen loading zone or in communication with the screen loading zone may be fitted with a rack for holding packing material such as a protective box to be fitted to a screen panel or protective sheeting to be fitted to one or both faces of the screen panel. The screen carriage delivers the cleaned screen panel to the rack where it is inserted in the box or placed adjacent the sheeting. For example by use of a robot arm.

It will be appreciated that features such as the finishing jet system, second storage rack for cleaned screen panels, the screen drying module, or the automated screen packing system may be fitted to apparatus for cleaning screen panels in various different ways. Thus in addition to making use of these features in the apparatus and methods according to the first and second aspects of the invention they may be employed in an apparatus according to a third aspect of the invention.

According to a third aspect the present invention provides an apparatus for cleaning screen panels comprising: an enclosure including a screen loading zone and a screen washing zone in communication with the screen loading zone;

at least one screen carriage formed and arranged for mounting at least one screen panel thereon and for transporting a said screen panel, edge first, into the screen washing zone;

wherein the screen washing zone has screen washing jets mounted for washing both faces of a screen panel mounted on the carriage.

Any one of the finishing jet system, second storage rack for cleaned screen panels, screen drying module or automated screen packing system may be fitted to an apparatus according to the third aspect. For example the screen carriage may be formed and arranged to carry the screen panel through the screen washing zone and not to reverse back out. the carriage continues through into a zone or module in communication with the screen washing zone where one or more of a finishing jet system, second storage rack for cleaned screen panels, screen drying module or automated screen packing system may be fitted. Other features described above with respect to the first aspect of the invention may also be provided for an apparatus of the third aspect of the invention as appropriate. According to a fourth aspect the present invention provides a method of cleaning a screen panel comprising: providing an apparatus according to the third aspect of the invention described herein; loading a screen panel onto a screen carriage of the apparatus positioned in the screen loading zone; transporting the screen panel into the screen washing zone; and operating screen washing jets in the screen washing zone to wash both faces of the screen panel with a cleaning fluid.

Description of Some Embodiments by Way of Example

Further preferred features and advantages of the invention will appear from the following detailed description given by way of example of some preferred embodiments illustrated with reference to the accompanying drawings in which:

Figures 1 a, 1 b show in schematic perspective view a screen cleaning apparatus; Figure 1 c shows the apparatus of figures 1 a andl b in end elevation;

Figure 1 d shows the apparatus of figures 1 a to 1 c in plan view;

Figure 2 shows schematically a screen cleaning system; Figure 3 shows in schematic perspective internal components of the apparatus of figures 1 ;

Figure 4 shows another screen cleaning apparatus in schematic elevation, Figure 5 shows the use of lateral dividers in a screen cleaning apparatus, Figure 6 shows in plan schematic view an alternative screen cleaning apparatus,

Figure 7 shows in plan schematic view a further alternative screen cleaning apparatus, and

Figure 8 shows in plan schematic view a yet further alternative screen cleaning apparatus.

Figure 1 a shows a screen cleaning apparatus of the invention being loaded with screen panels. The apparatus has an enclosure 1 in the general form of two boxes 2,4 of metal paneling, typically stainless steel, connected together. One of the boxes 2 has a door 6 in the form of a lid that is hinged 7 and is shown in an open position. The interior of box 2 constitutes a screen loading zone 8 of the enclosure 1 and the interior of box 4 constitutes a screen washing zone 9. The enclosure sits on a base 10 with a space 1 1 provided for a sump (see figure 1 c). A screen panel 12 has edges 14a, 14b formed for clamping onto a frame in a shale shaker. The panel 12 is shown being loaded into the screen loading zone 2. In this example the screen panel is self supporting as the mesh of the panel 12 bonded to an apertured plate (detail not shown). The panel 12 has some curvature as is common where screen panels of this type are used in a so called crown deck arrangement in a shale shaker. Figure 1 b is the same view as figure 1 a except that panel 12 has been loaded into the loading zone 8 and sits alongside another two panels. The panels 12 have been loaded onto carriages as shown and discussed with respect to figure 3 below.

Other external features of the apparatus include an air intake 16 on one end of box 2 in the form of a panel having tortuous paths there through to allow air to enter and prevent significant escape of cleaning fluid. This inlet for air may be provided with a noise reduction system to reduce noise escaping from the apparatus during cleaning operations e.g. a panel of air permeable sound reducing material. A corresponding air extraction point 18 at the end of box 4 can be used to extract air and harmful vapours in the conventional manner. Thus when the door (lid) 6 is closed (figure 1 d) the enclosure 1 can be used to contain harmful vapours that are extracted out of outlet 18.

Inspection hatches 20, 22 are bolted onto sides of boxes 2 and 4 and can be removed for inspection repair and replacement of internal components.

A hood 23 is provided at one end of box 4 in this example, to shield the inlet connections for services such as compressed air and washing fluid (see figure 2). Figures 1 c and 1 d show the enclosure 1 of figures 1 a, 1 b in end elevation and plan views respectively. In figure 1 c the sump 24 and sump outlet 26 can be seen. Loading zone rinse water jets 27 are shown at the top and one end of box 2 interior. Screen panel washing jets 30 are shown in the interior of box 4 adjacent the entrance from box 2. In this example three jets 30 are provided at each side of box 4 proximal to the start of the screen washing zone 9. Each group of three jets 30 are in a vertical relationship and the principal direction of spray as indicated by arrows Y close to but not at right angles to the direction of travel indicated by double headed arrow X (discussed further with reference to figure 3). Arrows Y in this example point at a slight angle from normal towards the rear of box 4, away from box 2.

Also shown in figures 1 c and 1 d are faces 28 of box 4 that shield box 2, to some extent from spray emitted from jets 30. These faces constitute shuttering at the entrance 31 to the screen washing zone 9 from the screen loading zone 8. Dashed lines in figure 1 d indicate the presence of three pairs of rails 29 running along inside the top of box 4, discussed below and with reference to figure 3.

Figure 2 shows in side elevation an apparatus of the form shown in figures 1 in a schematic diagram with various services supplied. Actual cleaning fluid, pneumatic and electrical connections are not shown, for clarity. A controller 32 is used to control operation of pumps and valves and thereby the screen panel cleaning process.

A compressor 33 supplies compressed air for pneumatic power inside enclosure 1 . The compressed air produced by the compressor is routed through controller 32 and then fed as required to the enclosure 1 via appropriate lines 33a (only one shown). A pump 34 supplies cleaning fluid to cleaning jets 30 and rinse jets 27 from a supply 36. In this example the sump is emptied by use of a pump 38. The action of all these components and associated valves is controlled by controller 32 as suggested by dashed lines 40.

Figure 3 shows internal features of the enclosure 1 shown in the preceding figures. For clarity pneumatic piping and valves, washing fluid piping and valves and the like are not shown in the figure. The cutaway perspective view shows three carriages 42 in side by side relationship. Each carriage is formed to mount a screen panel 12 as shown in figures 1 a, 1 b. Each carriage has a base 44 in the form of an elongate box section member with upstanding screen panel support members 46,48 - carriage ends in this example - to support screen panels. The carriage ends 48 nearest the box 4 (whose interior is the screen washing zone 9) also include shuttering 50 to aid in reducing the amount of spray and dislodged solids that may come back into the screen loading zone 8 during a cleaning operation. To aid in supporting screen panels the carriage ends are in the form of elongate slots 52 into which the edges of screen panels (parts 14a, 14b in figure 1 a) can fit. In this example the carriage ends 46,48 also include projections 54 at their tops used to hook about the carriage ends to provide additional support and ensure screen panels are inserted in the desired orientation for efficient cleaning.

Each carriage 42 in figure 3 is bolted to a shoe 56 (bolted connection visible by partial cutaway of bases 44 in this view). The shoes 56 are each connected to a double headed pneumatic powered piston fitted inside a cylinder in the interior of a respective rail 58. In this example the shoes 56 each wrap round their respective rails 58 and the connection to the pistons, contained in the cylinders within the rails, is through a slot underneath the rail. This arrangement aids in prevention of entry of solids and fluid to the piston and cylinder mechanism.

The rails 58 are supported above the bulk of sump 24 by fixing to cross braces 62,64.

Also shown are pairs of pins 66 that fit into between rails 29 (figure 1 d) fitted inside the roof of box 4 and providing bracing to keep carriages upright when in motion and subject to lateral forces from the screen washing jets. Operation of a typical screen panel cleaning procedure will now be described. Screen panels 12 are loaded onto carriages (42, figure 3) in the screen loading zone 8 and the door 6 is closed (figures 1 ).

The controller (32, figure 2) is then switched to carry out a cleaning process operating pumps and valves in a predetermined sequence. Each carriage 42, shown in figure 3, is moved by pneumatic power, in turn, from the screen panel loading zone 8 into and then out of the screen panel washing zone 9, along its respective rail 58, as suggested by double headed arrow X (figure 3). The speed of motion can be adjusted by experience to suit the degree of cleaning concerned. As each carriage 42 moves into and then out of the screen washing zone, screen washing jets 30 operate to clean the screen panel carried by the carriage. Screen rinsing jets 27 may also operate to initiate and/or to complete washing.

Once all three screen panels have been into and out of the screen washing zone 9 and any final rinsing period completed the door 6 can be opened, the cleaned screens removed and more screens loaded for cleaning. Used cleaning fluid and solids collected in the sump may be pumped away using sump pump 38 operating as washing proceeds or after an accumulation of washings in the sump. In this example the sump 24 includes sump washing jets 25 formed to wash down solids in the sump to the outlet 26 (figure 1 c). Typical washing times for screen panels such as generally used in shale shaker operations may be only of the order of 30 seconds each. Thus with the apparatus of figures 1 to 3 , three screen panels may be cleaned very rapidly with little operator time required. The use of the apparatus therefore allows rapid cleaning of screen panels so that they can be readily exchanged for dirty screen panels on a vibratory screening machine, keeping screening operations going whilst avoiding running with blocked or partially blocked screens for extended periods of time.

Figure 4 shows an alternative apparatus in schematic elevation and generally of the similar construction to that of the preceding figures. It can be supplied with services and controlled in the same way as the arrangement of figure 2. The enclosure 1 has screen loading zone 8 vertically above screen washing zone 9. Motion of carriages 42 (only one shown in this figure, but typically three in side by side relationship are provided) is therefore down and then up as indicated by double headed arrow X. In this example door 6 in a side of box 2 is shown open. The carriages 42 for mounting screen panels have a base 44 in the form of a an elongate box section with shuttering 50 (as in the example of figure 3), an upstanding screen panel support member 46 at the back of box 2 and connecting to a top support member opposite and parallel to base 44. See figure 4a showing a side view sketch.

Base 44 and top member 68 may be in the form of elongate slots(not shown for clarity) to fit about the edges of screen panels in similar fashion to the slots 52 shown in figure 3. Such a slot may also be supplied on the screen panel support member 46, depending on the type of screen panel being supported Projections 54 (figure 3) may also be used if desired.

The carriages 42 may be pneumatically powered as for the apparatus of figure 3 with a shoe 56 connecting either to base 44 or to support member 46 (figure 4a). The shoe runs on a rail 58 operating vertically (not shown in figure 4 but see figure 4a) to provide the desired vertical motion to the carriages 42.

The sump 24 is provided at the bottom end of box 4 for removal of used washing fluid and solids. In use of the apparatus of figure 4 screen panels are loaded onto carriages via the door 6 which is then closed and similar cleaning procedures as described for the apparatus of figures 1 to 3 employed. The screen panel washing jets 30 are at opposite sides of box 4, at the entrance to the screen washing zone 9. The principal direction of spray as indicated by arrows Y is close to horizontal, across box 4, but angled slightly downwards.

As an alternative arrangement door 6 may be replaced with a fixed side to box 2 and the top 70 of the box made an opening lid. In this case the carriages may be formed in the form indicated in figure 4b showing a side view sketch, with two upright screen panel support members 46,48 to facilitate top loading of screen panels. The screen panel support members 46,48 may be in the form of elongate grooves to fit about screen panel edges as described above with respect to the embodiment of figure 3.

Figure 5 shows in plan view an apparatus similar to that of figures 1 to 3 with like parts numbered the same. In this view the lid of box 2 is omitted to allow viewing inside the screen loading zone 8. In use of the apparatus a lid 6 such as shown in figures 1 would be employed. The screen loading zone in this example includes three carriages 42 which are separated by dividing panels 72, 74 running in the direction of travel of the carriages X and therefore dividing the screen loading zone 8 into three compartments, each having a carriage 42, when the carriage is in the loading zone. The panels 72,74 prevent spray of cleaning fluid and solids exiting from the screen washing zone 9 into the screen loading zone 8 reaching an adjacent carriage 42 and its load of a screen panel. The dividing panels 72,74 can be of the same depth as box 2 and fixed to its end walls 76,78. The dividing panels may also be fixed to transverse bracing struts at the base of box 2 and above the sump, in the same manner as the strut 64 supports the rails 58 in figure 3.

Figure 6 shows in schematic plan view an alternative apparatus. In this view the top of the apparatus is not shown to allow viewing of the internals. Like parts are numbered the same as in the earlier figures. In the screen loading zone 8 a storage rack in the form of a rotating carousel 78 is provided. The carousel can be loaded with a number of screen panels 12 for cleaning. Screen carriage 42 is formed to pick up a screen panel from the carousel and take it into and then back out of the screen washing zone 9 (suggested by double headed arrow X). The cleaned screen panel is then returned to its place on the carousel 78 which then rotates (arrow R) to allow the carriage to pick up the next screen panel 12 and so on until all the panels loaded on the carousel have been cleaned.

Figure 7 shows an apparatus in a similar schematic plan view to that of figure 6. In this apparatus the screen panels are loaded on to a storage rack 80 in side by side relationship. Screen carriage 42 is formed to move in two directions as indicated by double headed arrows X and Y. In the direction X a screen panel can be taken into and out of the screen washing zone 9. In the direction Y the screen carriage may index up and down rack 80 to pick up a selected screen panel 12 or return it to its location. In this example the box 2 includes a second rack 82 in the loading zone to which cleaned screen panels may be carried by carriage 42. The second rack is in a drying module, defined by partition 85 and the sides of box 2. A warm air inlet 86 provides a drying means. Also featured in this example are jets 88 provided to spray cleaned screen panels with anti corrosion (preserving) fluid if desired.

Figure 8 shows an apparatus similar to that of figure 7 in a similar plan view. In this example the second rack 82 is part of a screen packing system. Cleaned screens are delivered by the carriage 42 to storage rack 82 where they are inserted into boxes 90 and may be sealed therein by a suitable taping system (not shown) if desired

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.