Abstract: A retractable guard for use in combination with a sewage pipe leading from a flush toilet is provided having a plurality of prongs with hooked ends positioned within a cross section of the pipe. The prongs are connected to a piston which is slidable within a cylinder, perpendicular to the pipe. Flushing the toilet causes water to be directed in the cylinder which in turn partially retracts the prongs. Water may be diverted from the cylinder to wash accumulated debris from the prongs.

Abstract: A multi-stage filter for filtering injection molding melt includes an elongate filter element having a filter inlet end, a filter outlet end and a plurality of filter stages axially disposed on the element and adjoining each other. Each filter stage includes a plurality of axial filter grooves in its outer surface which are spaced apart from a filter chamber wall to define a distinct filter clearance for each filter stage. The axial filter grooves are circumferentially spaced apart from each other and alternate with axial grooves axially extending between adjoining filter stages which define melt transfer passages to transfer melt between filter stages.

Abstract: A filtration apparatus suitable for use in peridural anesthesia formed of two mating sections and a membrane positioned between and supported by the sections. Each section has an liquid inlet or liquid outlet and are joined together to form a chamber therebetween. The membrane is positioned at an angle between about 5.degree. and 15.degree. relative to the axes of the inlet and outlet.

Abstract: Apparatus and method for isolating and blocking articles flushed down toilets before they can get into and jam a main sewer line utilizes a threaded rod having a head for rotation thereof disposed on one end, a nut threaded onto the rod, a flat washer disposed next to the nut on the opposite side therefrom from the head, and a rubber washer disposed next to the flat washer on the opposite side therefrom from the nut. In a preferred embodiment, the rod is threaded into a threaded hole in a cleanout plug adjacent a toilet to be isolated and the nut tightens against the cleanout plug to compress the rubber washer to seal in sewer gases and fluids.

Abstract: The present invention sets forth an adapter for filter cartridges and a mating cartridge which provides sealing means between the cartridge and the adapter and sealing means between the adapter and a filter head to which it is to be installed, and means for installing the adapter on a cartridge and for installing the adapter in the filter head with an aligning and locking means that ensures that all parts are appropriately positioned for proper function and at the same time will prevent physical disengagement and/or a break in the flow path from the cartridge to the filter head when the cartridge and adapter are properly installed in the filter head.

Abstract: A filter changing apparatus for use in an extrusion press, comprising a frame, filter support members hydraulically displaceable in the frame, in a direction which is substantially at right angles to the flow of material through the press and filters disposed in each of the filter support members, at least one of the filter support members being detachably mounted in the frame, and a support member for discharging residues of rubber or thermoplastics material from the extrusion press, the support member being detachably mountable in the frame in place of the at least one detachably mounted filter support member, the support member having associated therewith a discharge plate for displacing residual material in the extrusion press to a discharge station.

Abstract: A modular water conditioning apparatus for filtering or adding substances to water or similar fluids has a filter assembly with a hollow cylindrical casing extending perpendicularly upwards from a cylindrical base section. The base section has coaxial inlet and outlet tubes disposed perpendicularly outwards from opposite cylindrical walls of the base section. Within the base section, a hollow cylindrical boss, coupled to the outlet pipe, extends upwards. Cylindrical filter elements contained within the casing of the filter assembly are held in position and forced into sealing contact with the outlet boss by a cup spring pressed down on the upper surface of the filter element by a cap screwed down on the upper open end of the filter casing. Filter assemblies can be cascaded by inserting an outlet tube into the larger diameter inlet tube of an adjacent filter assembly.

Abstract: An in-line, inclined strainer device in which the strainer proper is removably mounted within a casing, which casing is mounted in-line in a piping system, such that the strainer may be removed in an easy manner for subsequent replacement and/or cleaning. The strainer is mounted by a removable tubular element having an elliptically-cut end for mounting directly to it an elliptically-shaped screen mesh forming the strainer proper. The end of the tubular element is mounted in a linear portion of a casing through which flows the liquid of the piping system, so that the screen mesh may entrap solids. Diametrically opposite to the tubular element is a drainage duct which, when opened, allows the flow of the liquid to pass through, carrying away with it the effluent sedimented and debris in the drainage duct. The strainer proper includes a plurality of rods that are welded to the lower end of the tubular element, which rods directly mount the screen mesh.

Abstract: A process and apparatus for filtering a polymer which passes through a heated, high pressure filtering chamber across which a filter members passes and in which sealing plugs made of the substance being filtered are formed within entry and exit zones thereof. A plug removal zone is provided between the entry port for said filter and the outflow aperture of the filtering chamber. The zone is provided with a valve to permit removal of sealing plug material when in a heat-softened state. A cooled, substantially rigid plug of polymer is formed initially. Thereafter, the plug is heated at one end to soften it and to permit displacement of a part of it through the valve by fresh, hot polymer. In alternative embodiments, the plug removal zone is not needed and the plug is permitted to pass into the passage but is then diverted before meeting the main flow of substance being filtered.

Abstract: A filter apparatus having a hollow, T-shaped body, the upper portion of the "T" defining a fluid flow path and the lower portion of the "T" defining a filter housing portion. A baffle plate is positioned in the "T" to direct fluid into a filter element retained within the filter housing portion of the housing. A first end of the filter element extends into an aperture in the baffle plate and is retained thereby. A second end of the filter element is coupled to a base, a portion of which extends externally to the housing. The externally extending portion of the base may contain data regarding the filter element. An aligning pin and alignment tab for such externally extending portion of said base may be provided to facilitate assembly of the filter apparatus.

Abstract: A large diameter pipeline strainer has a body with a central chamber and an axially aligned inlet and outlet a lateral opening covered by a removable cover plate to allow removal and replacement of a strainer element mounted in the chamber. The strainer has first and second perforated conical sheet metal walls with an outer wall tapering from the inlet toward the outlet and an inner wall tapering from the outlet back to an apex at the inlet. The strainer is positioned by an annular bead at the inlet sealing against the body at the inlet and fitted within an annular groove formed in both the body and the cover. The strainer is supported at the outlet by a number of radially extending projections which engage the strainer at the point where the inner and outer walls are joined together.

Abstract: A multiple-disc type fluid filter is described wherein the housing includes an outer tubular section, and an inner section having two tubular members with an end plate at one end of one tubular member and securable to an open end of the outer housing section. The two tubular members of the inner housing section include ribs for supporting the filter discs. The end plate and the tubular member to which it is secured are open and constitute one of the filter ports, e.g. the inlet port, and the opposite end of the same tubular member is closed and terminates short of the outer housing section. The second tubular member, which is longitudinally spaced from the closed end of the first tubular member, constitutes the other filter port, e.g. outlet port. The stack of filter discs are all of substantially the same uniform thickness, but there are included a plurality of further discs of non-uniform thickness such as to correct the accumulation of non-uniformities in the latter discs.

Abstract: A drainpipe straining device can be attached either through an existing cleanout hole within the drainpipe or can be releasably secured to the drainpipe through a radial hole formed in the pipe. The device includes a plug member having substantially axially extending bristles. The shank of the plug member may be received within the bore of a cleanout hole already provided in a drain structure, or releasably received within a bore formed in a ring adapted to be secured to a radial hole drilled into the drainpipe. The ring member can be secured by strap means to the drainpipe and held in place thereon to releasably receive the plug. Solid materials will be received and collected by the bristles on the drain plug and can be removed from the drainpipe simply by removing and cleaning the plug and associated bristles.

Abstract: Spa recirculation water filter installation having an upwardly, inwardly open recess in the plastic spa water reservoir molded in a similar recess in a female mold. Water outlet fittings in opposite walls of the recess connected in a T-manner to a recirculation water pump. A filter having in each end a fitting interengaging with the water outlet fittings to secure the filter in place. A compression spring in one filter end fitting to be compressed during engagement and disengagement of the filter end fittings with the water outlet fittings. A cover over the filter installation with flanges secured to the filter end fittings.

Abstract: A diverting plate having the same external configuration as a changeable strainer in a flow line for a molten polymer. Contamination is removed by substituting the plate for a strainer.

Abstract: An improved filter screen device is provided which comprises an elongated, tubular housing, a hollow elongated perforated tubular member releasably secured in the hollow central interior of the housing and a flexible sock-type filter screen releasably disposed over the outer surface of the tubular member in the housing. The housing includes an open upstream end which is closed by the tubular member and a closed opposite downstream end. An inlet is disposed at an acute angle to the length of the housing and intersects the housing interior between its upstream and downstream ends. A first outlet is disposed at the downstream end along about the longitudinal axis of the housing so as to communicate with the interior of the hollow tubular member. A second outlet is also disposed in the downstream end of the housing at an angle to the first outlet and communicates with a space between the filter screen and the housing.

Abstract: A debris separator for rain gutter systems includes a substantially tubular housing having an upper port, a lower port, and an expanded chamber beneath the top port having a transverse opening. An inclined grate is secured within the chamber to extend angularly upwardly from the bottom peripheral edge of the transverse opening so as to extend across the chamber and the top port. Preferably, the grid includes a plurality of spaced, parallel plates which permit water to fall therebetween while diverting large particulate along the grid to direct it out of the housing through the transverse opening .

Abstract: A slide plate screen changer has a housing defining a material flow passage and a transverse slide plate passage in which is mounted a movable screen plate. Seal rings on the upstream and downstream sides respectively of the screen plate prevent leakage of material from the flow passage. One of the seals is adjusted by means of a threaded bushing which surrounds the flow passage and which protrudes axially from one end of the housing where it is fully accessible to torque exerting tools.

Abstract: An apparatus is disclosed for separating leaves, debris, dirt, and sediment from rain water. The apparatus is comprised of a drawer-containing accumulating device insertable in the leader pipe bringing rain water from a roof by way of a gutter. The drawer in the device contains a screen for separating leaves and debris from rain water. The drawer is periodically removed and emptied.

Abstract: A disposable filter device having a plastic housing with inlet and outlet chambers separated by a filter disc sealed within the housing, the housing being readily disassemblable after use to remove the filter disc for identification or analysis of the material filtered from the fluid.

Abstract: A blood and perfusate filter apparatus having a pair of molded housing members that are substantially identical in their configuration. The upper housing member having a pyramidal-shaped reservoir formed in the upper surface thereof which acts as a secondary distribution reservoir, and the lower housing member having a pyramidal-shaped reservoir formed in the lower surface thereof which acts as a secondary collection reservoir. Interchangeable tubing couplings are press-fit bonded to inlet/outlet ports located in the secondary reservoirs. A filter element, mounted in a resinous band, is bonded between the housing members so as to filter blood or perfusate as it passes through the filter. The filter element also forms primary distribution and collection reservoirs with respect to the upper and lower housing members. Different types of filter configurations, such as flat or pleated, can be mounted in a resinous band and used as the filter media.

Abstract: An improved low-profile inline fluid filter (10), for IV sets and the like, comprises only two discrete units: a shell unit (11) and a screen unit (12). The screen unit (12) is adapted to fit substantially within the shell unit (11) such that the screen unit (12) and the shell unit (11) are connected to each other at both ends.

Abstract: A method for early detection of mastitis in cows, effected during normal milking of cows in a milking parlor, by monitoring the milk taken from each cow for the presence of milk clots, comprises cutting the vacuum milk line to each milking station and inserting a filter-detector therein between the claw and the recorder jar. Each filter-detector comprises a flat-sided transparent casing with a lateral slot which receives a self-sealing slide carrying the filter element. The slide carrier preferably has an integral bypass aperture so that vacuum conditions at the claw end are retained even after the filter element has become blocked. The slide carrier is preferably constructed so that, when in position in the casing, a seepage passage remains between the slide and the casing inner wall, so that cleansing fluid can pass during normal in-place cleaning of the installation.

Abstract: In a screw extrusion device used for extruding plastics materials, a filter or tool-carrier is disposed at the downstream or outlet end of the extruder, an annular pressure element bearing on the carrier so as to secure and seal the carrier in its operative position. The carrier is displaceable perpendicularly to the flowpath of the plastics material so as to permit facile changing of the filter element. The annular pressure element is acted upon by hydraulic fluid, the hydraulic circuit including an annular pressure chamber. The inner and outer walls of the chamber are formed, respectively, by concentric metal bellows. One end of each bellows is mounted on the pressure element and the other end thereof on a housing.

Abstract: Filters, particularly relative small filters, usually include a screening element which readily clogs or becomes partially blocked with material thus impeding the flow of liquid therethrough. The present invention comprises a cylindrical filter housing or bowl portion bisected by a vertically situated screen element situated at an angle to the direction of flow so that the flow of fluid tends to wash the screen and deposit the sediment at the base of the housing. Preferably the housing is formed of clear plastic or glass so that the screen condition can be viewed. The base of the screen element is angulated and lies on the base of the housing upon the inlet side thereof so that when removing the screen for cleaning, any sediment may be lifted clear of the housing as the screen is removed.

Abstract: A modular block for osmotic methods of separation under pressure can be folded open and the filtration unit can easily be removed and introduced in the process. The filtration unit consists of a base plate with a membrane filter candle, and the filter candle consists of a stack of membrane filter plates. Spacers are placed between the filter plates and deflecting plates are provided to ensure zigzag penetration. The permeate transportation is displaced to the edge of the plates. The permeate issues laterally at the flange.

Abstract: A drain trap includes a J-shaped pipe section having an opening at one end of the horizontal portion. A removable tray is inserted through the opening and covers the bottom of the horizontal portion on the inside thereof. The tray has sides extending part way up the sides of the horizontal portion. An end cover on the tray is adapted to cover and seal the opening. A U-shaped spring clamp extending across the back of the end cover holds the cover against the pipe section. The tray is provided with three groups of vertically extending fingers which strain material such as food and hair from water flowing through the pipe section. This material can then be disposed of by removal of the tray from the pipe section.

Abstract: A water strainer is comprised of a body which contains a central chamber with which the inlet and outlet passages communicate. Strainer grids angularly oriented with respect to each other meet to form the apex of a triangle within the central chamber adjacent the inlet passage. Debris and foreign material caught on the grid is washed by the flow of water through the strainer towards regions near the side of the interior of the body where it will not impede the flow of the mainstream of the water through the grid, or cause an unsymmetrical flow velocity profile in the water stream issuing from the strainer.

Abstract: A filter assembly for extruded polymer melts is described which comprises a filter having retained between inlet and outlet manifolds with a contact pressure that can be varied. A primary seal device between the manifold and the housing is located in a rabbet in either the housing or the manifold at the contact plane. This seal responds to pressure from the polymer melt flow by deforming and increasing the contact pressure between the manifold and the housing. Thus the greater the pressure at which the melt is extruded, the tighter is the seal.

Abstract: A slide-plate filter apparatus particularly for plastic stock under pressure in which rigid filter plate sections carrying corresponding sections of filter media are fed in a continuing sequence across the flow path of the plastic stock is provided with off-set retainer plates for directing plastic stock which is forced between the filter plate sections into a path which includes filter media, so that no unfiltered plastic stock can pass through the apparatus.

Abstract: A change device for sieves used for filtering plastic materials. The change device comprises a sieve holder having a bore for the throughflowing material and a slot extending transversely thereto, in which there are sealingly retained in work position sieve supports or carriers containing sieves. By means of a work cylinder it is possible, without interrupting the transport of the material which is being processed, to eject and replace the contaminated sieve by a new sieve. The rapid change device is particularly suitable for installation in an extruder for fabricating rubber hoses for automobile tires, the installation of such rapid change device advantageously being accomplished between the extruder and the injection head.

Abstract: A fluid filtering device is provided for connection with a fluid line. The fluid device includes a housing having a fluid inlet on one end, a fluid outlet on the other end and a fluid passage formed through the housing. The fluid passage connects the inlet with the outlet and includes a port formed along its length. A tubular filter element open at one end is removably insertable into a filter chamber formed within the housing and, upon insertion, is axially slidable between a first position in which the open end of the filter element abuts against the fluid port and a second position in which the open end of the filter element is spaced from the fluid port. A spring urges the filter element toward its first position. In operation the fluid flow into the housing inlet passes through the port and into the interior of the filter element. The fluid then flows through the filter element and to the housing outlet.

Abstract: Filtration apparatus in which the filter medium is mounted at a slope with respect to the horizontal and in which there are means to vibrate the medium in a horizontal direction to assist the cleaning of the medium. A single chamber may contain many sheets of media, one version of the apparatus comprises a plurality of separate modular structures each containing at least one filter medium and in another version modular structures are so designed that they assemble into a stack and when so assembled form the necessary conduits by which each filter medium communicates with the necessary inlets and outlets for the relevant materials.

Abstract: A filter holding assembly capable of being used to filter pressurized fluid from a source of the latter, with the assembly capable of being dismantled without the use of hand tools to occupy a minimum of space, and the assembly likewise capable of being transformed without the use of hand tools to a unit in which first and second mating plates support a large diameter filter membrane in a position to be subjected to the pressurized fluid. Particulates in the fluid above a predetermined size are deposited on the membrane, with the balance of the fluid discharging as a filtrate from the assembly. The first and second plates when in mating engagement define a centered confined space in which the membrane and a supporting screen are disposed, and the membrane having the peripheral edge portion thereof in sealing contact with a compressed resilient ring to prevent the pressurized fluid in the centered confined space by-passing the membrane.

Abstract: Safety device for oil filters and the like, having a casing containing a filtering cartridge, wherein a piston is entered with a frictional fit in said casing against a spring means, said piston being forced towards the bottom of the casing into a waiting position by the insertion of said cartridge; at least one oil passage being provided through said piston, said spring means returning the piston in its active position upon removal of the cartridge from the casing and a means being provided for releasably locking said piston in its active position.

Abstract: A fluid filtering device is provided for connection with a fluid line. The fluid device includes a housing having a fluid inlet on one end, a fluid outlet on the other end and a fluid passage formed through the housing. The fluid passage connects the inlet with the outlet and includes a port formed along its length. A tubular filter element open at one end is removably insertable into a filter chamber formed within the housing and, upon insertion, is axially slidable between a first position in which the open end of the filter element abuts against the fluid port and a second position in which the open end of the filter element is spaced from the fluid port. A spring urges the filter element toward its first position. In operation the fluid flow into the housing inlet passes through the port and into the interior of the filter element. The fluid then flows through the filter element and to the housing outlet.

Abstract: A fluid filtering device is provided for connection with a fluid line. The fluid device includes a housing having a fluid inlet on one end, a fluid outlet on the other end and a fluid passage for connecting the inlet to the outlet. The fluid passage includes an elongated cylindrical wall portion along its length. A filter assembly comprising a tubular filter element open at each end and a cap attached to a first axial end of the filter element is insertable within the housing so that the other or second end of the filter element is received within and sealingly engages the cylindrical wall portion of the fluid passage when the cap is connected to the housing. With the filter assembly thus positioned, the outer periphery or exterior of the tubular filter element is open to the housing inlet while, conversely, the interior of the filter element is open to the housing fluid outlet.

Abstract: A rapid cleaning filter utilized in a liquid fertilizer system including an elongate tank having a screen filter element longitudinally disposed in the tank with an entry slot in the end of the tank for quick removal from the tank; sealing means around that portion of the filter element extending outwardly of the tank and a quick release latching arm for holding the element in sealing relation with the tank.

Abstract: A high volume low pressure drop filter is provided which comprises a housing containing a plurality of filter panels hinged in accordian form. The filter panels in filtering position have an upwardly facing V-configuration. The panels are readily replaced by moving the active panels into an inactive position and drawing a fresh pair of panels into the position occupied by the panels which were removed.

Abstract: A high capacity low pressure drop flow line filter apparatus of standardized pipe dimension having an interchangeable filter apparatus disposed therein. The filter apparatus is provided with means for positively securing within the apparatus while compensating for dimensional variations in the filter apparatus to provide for such interchangeable use.

Abstract: Apparatus for forming plastic melts into strands or filaments wherein molten plastic material is delivered by a pump from a container through a feed line to a distributor means which has a first outlet for the molten plastic material to be processed and a second outlet to a return line leading back to the container, and a control valve is located in the return line to regulate the return of flow of the plastic material to the container, the return flow of the plastic material to the container, the return line and associated control functioning to avoid undesirable plugging of the apparatus or damage to the plastic materials during interruptions in operations, and the like.

Abstract: Filtering apparatus having a housing defining an inlet and an outlet. Disposed within the housing is a plurality of filter elements constructed in tubular form and held together as a bundle of such elements. The entire bundle of elements may be removed from or inserted into the housing as a unit. Each of the tubular filter elements has a threaded fitting at each end thereof with the threads on each of the ends being adapted for mating engagement with each other. In this manner a plurality of the filter elements may be assembled in tandem form by threaded engagement of the mating ends thereof to provide the desired filter area and size for any particular application without the necessity of custom designing filter elements for each housing or application. The mating threads are formed on dissimilar non-galling metals.

Abstract: The invention relates to a dirt filter for water pipes of the type used for carrying water for household and industrial use. The filter defines inlet and outlet chambers with an apertured dividing wall therebetween. An upper lid and a lower dirt collecting container and attached with threaded connections to the housing. A filter insert is disposed between the lid and the dividing wall and the insert has a carrier with upper and lower cylinder rings which respectively engage the lid and the chamber dividing wall. The interior of the filter has fluid communication with the inlet chamber through the opening in the chamber dividing wall. An annular, cup shaped insert keeps the flow in the inlet chamber away from the interior of the dirt collecting container but permits the drop of dirt into this container.

Abstract: A slide filter for filtering plastic stock and other materials having a slide plate movable within a housing, across the path of material flow. The housing contains sealing means to prevent leakage of the material to the outside of the housing. The slide plate includes one or more recesses bounded by wall means within which a mechanical screen or sand pack filter is positioned.

Abstract: An arrangement for filtering fluid flow includes a T connection having a hollow body connected with two aligned hollow lateral extensions. A plate is secured within and intersects the lateral extensions and has an opening therein to accommodate flow through the lateral projections. A filter member including a hollow core is positioned adjacent the plate and surrounds the opening in the plate for filtering flow through the lateral extensions. The filter member extends from the extensions into the body and is closed off at one end by a flange secured to the body.

Abstract: A trap for use with waste water lines for sinks, laundry tubs and the like has a dip portion for retaining liquids to prevent the reverse flow of noxious gases. The lower wall of the dip portion has an opening which is smaller than the interior diameter of the trap and which is adapted to receive a closure plug. A plug for closing the opening is arranged to support a blocking member in the interior of the dip portion of the trap. The blocking member comprises a plurality of flexible fingers which are held in spaced apart relationship on a toroid such that the exterior surfaces of the fingers taper outwardly from the supporting toroid to dimension such that the fingers in combination form a circle which approximates the interior diameter of the trap and the fingers then taper inwardly until the tips of the fingers in combination define a circle of approximately the same dimension as the toroid.

Abstract: A fluid filter including a filter body having inlet and outlet passages communicating with an open ended chamber on opposite sides of a tapered seat area. A cupshaped fluid filter or strainer element is located in the chamber through the open end thereof and is adapted to be closely received in the seat area. A bonnet assembly covers the open end of the chamber, is threadedly mounted to the body and is comprised of a bonnet, a bonnet nut and biasing means. The biasing means is employed to exert a biasing force against the filter or strainer element to continuously urge it toward the seat area. At least the bonnet and bonnet nut are themselves interconnected in a manner that permits both rotational and limited axial movement therebetween. The disclosed structure facilitates access to the chamber and filter or strainer element without the necessity for removing the entire fluid filter structure from a service installation.

Abstract: The specification and drawings disclose a fluid filter device which includes a central body section clamped between a pair of end fittings by a plurality of longitudinally extending tie bolts. The tie bolt arrangement is such that only one bolt must be removed to permit the central body section to be swung out of position between the end fittings for filter cleaning, changing, or the like. The central body section includes a cylindrical through passage which extends longitudinally of the body perpendicularly to end faces which mate with the end fittings. A filter cartridge is received in the through passage and includes a cylindrical sleeve which is sized so as to be closely and slidably received in the passage. Filter elements are mounted within the sleeve. Additionally, seal rings are carried about the opposite ends of the sleeve to provide a fluid seal between the end fittings and the central body, as well as to prevent leakage between the outside of the sleeve and the wall of the passageway.

Abstract: A fluid filtering device comprises an inner member having an inner axial passageway for the fluid, and an outer housing radially spaced from the inner member to define therewith an outer axial passageway for the fluid, the inner member being formed with a radial passageway providing a communicating path between the two axial passageways for the fluid. A filter is disposed with the device upstream of the radial passageway in the path of the fluid flowing through the passageway, and a deflector is disposed within the axial passageway of the inner member on the upstream side of its radial passageway to deflect the fluid to flow through the radial passageway and through the filter. The deflector has a cylindrical wall disposed within the inner member and extending axially thereof, and a transverse wall extending transversely across the axial passageway of the inner member.

Abstract: A screen changer mounted between a flowable plastic extruder and a die has a clamp frame movable rectilinearly across the extrusion passage by fluid piston and cylinder means to successively position one of four screen blocks across the passage. A used block is removable from the frame at one end, whereupon latch mechanism retains three blocks while the frame retracts to receive a fresh block. Each block contains a filter recess, a purge recess and a pre-fill groove in the upstream face, so that the incoming block is pre-filled with plastic and purged while moving into position across the passage.