Abstract: A composite pipe comprises a polyetheretherketone innermost pipe around which a reinforcing overwrap is arranged. A protective sheath surrounds the overwrap. Such a composite pipe may be made by selecting a polyetheretherketone pipe having an outer region having a crystallinity of less than 25%; overlaying the selected pipe with overwrap; and subjecting the combination to heat, thereby causing the crystallinity of the outer region of the polyetheretherketone pipe to increase. The method reduces the risk of pipe failure.

Abstract: Single- or multilayer propylene polymer pipes and pipe components for pipelines with improved resistance to rapid crack propagation made from a propylene homopolymer with a melt index of 0.05 to 10 g/10 min at 230° C./2.16 kg or propylene block copolymer from 90.0 to 99.9 wt % of propylene and 0.1 to 10.0 wt % of a ?-olefins with 2 or 4 to 18 carbon atoms with a melt index of 0.05 to 8 g/10 min at 230° C./2.16 kg or mixtures thereof, wherein the propylene homopolymers or propylene block copolymers are ?-nucleated propylene polymers, and the propylene polymer pipes for pipelines made from the ?-nucleated propylene homopolymers have a rapid crack propagation characterized by a critical temperature of ?5 to +40° C. and a critical pressure?3 bar below the critical temperature and the propylene polymer pipes made from ?-nucleated propylene block copolymers have a rapid crack propagation characterized by a critical temperature of ?25 to 0° C. and a critical pressure?3 bar below the critical temperature.

Abstract: An apparatus for controlling water ingress into a pipe useful in the production of hydrocarbons from underground reservoirs comprises a multi-layer tubular, the multi-layered tubular comprising an outer pipe layer, an inner pipe layer longitudinally aligned within the outer pipe layer, and a hydrophilic composite material between the outer pipe layer and the inner pipe layer. The composite comprises a material selected from the group consisting of sand, silt and clay and mixtures thereof. The composite material is non chemically reactive and has absorption properties such that the material swells in the presence of water but is non-absorptive of hydrocarbons. Upon exposure to water, composite material creates an impervious shield covering at least a portion of the inner pipe layer.

Abstract: This invention relates to the use of a colored polyethylene pipe for transporting water containing disinfectant. The pipe is prepared from a polyethylene resin, that is produced with one or more single site catalyst systems, and that comprises blue pigments and anti-UV additive.

Abstract: A hose comprising a tubular body of flexible material arranged between an inner and an outer helically wound wire, the tubular body serving to transport fluid through the hose and to prevent fluid leakage through the body, the tubular body comprising a reinforcing layer and a sealing layer, wherein the hose further comprises axial strengthening strips extending along the length of the hose.

Abstract: Single or multilayer tube such as for use as airbrake tubing. At least one of the layers of the tube may be formed of a long-chain polyamide such as nylon 4-10, nylon 6-10, nylon 10-10, nylon 6-12, nylon 10-12, or nylon 12-12, or an alloy thereof.

Abstract: A flowpath assembly for a gas turbine engine includes a plurality of flowpath insert ducts arranged in a cascade configuration. Each flowpath duct includes a radially inward wall, a radially outward wall, a first side wall, and a second side wall. A flowpath volume is defined between the inward, outward, first side and second side walls. The first side wall of a given one of the plurality of flowpath insert ducts is positioned adjacent to the second sidewall of an adjacent one of the plurality of flowpath insert ducts in the cascade configuration.

Abstract: A sleeved composite pipe or piling structure formed of an elongated polyethylene pipe or tube of high-density polyethylene (HDPE) or another polyethylene material installed over a substantially rigid and incompressible hollow metal pipe or solid wood core having an outer diameter that is the same or slightly larger than a normal inside diameter of the polyethylene pipe or tube when measured in a relaxed state at ambient temperature. The polyethylene pipe or tube is, for example, a HDPE 3408 material formed of virgin PE 3408 resin as specified in ASTM D3350 with UV protection, and the pipe is produced to ASTM A-3408. The metal pipe core can be ferrous or nonferrous pipe.

Abstract: A conduit includes a multilayer wall including an outer layer having a first color; an intermediate layer having a second color; and an inner layer having a third color, wherein the intermediate layer is between the outer layer and the inner layer, and the first color, the second color, and the third color are different. Each of the first color, the second color, and the third color indicates a level of wear of the multilayer wall when one of the first color, the second color, or the third color is exposed due to wear or abrasion.

Abstract: A co-extruded multi-layer plastic pipe and method of manufacture are disclosed in which a first extruder melts and extrudes a first plastic material into the outer annulus of a coaxial extrusion die to form an outer pipe layer, and a second extruder melts and extrudes a highly oxidation-resistant plastic material into the inner annulus of said coaxial extrusion die under a blanket of inert gas to create an inner pipe layer, whereby the outer and inner pipe layers are fused together under the protection of the inert gas blanket which prevents premature degradation of the oxidation-resistant inner layer until the finished extruded pipe has cooled and solidified.

Abstract: A transfer member assembly 2 comprises a transfer member 4 for the transfer of a signal, power or fluid such as an optical fibre, an electrical conductor or a gas or hydraulic line. The transfer member assembly 2 comprises a shroud 6 formed around the transfer member 4 and a composite material 8 comprising a matrix formed around the shroud 6. The composite material 8 comprises longitudinal fibres in a resin matrix. The resin matrix penetrates at least part-way into the shroud 6. The penetration of the matrix into the shroud 6 is controlled during manufacture of the transfer member assembly 2, for example by controlling shroud permeability or by controlling the resin viscosity or pressure utilised in a pultrusion process utilised to form the composite.

Abstract: A composite pipe including an internal liner and at least one external layer made of a fiber reinforced consolidated thermoplastic material. A heat-resistant material mechanically separates the liner from the at least one external thermoplastic layer. The heat-resistant material forms a non-bonding barrier that is non-bonded to at least one of liner and the adjacent at least one thermoplastic layer. A method and an assembly for producing the composite pipe.

Abstract: Provided is an economical multilayered resin tube-shaped body that can be safely used in a high-temperature environment such as an engine compartment. A multilayered resin tube-shaped body (1) having excellent heat resistance is obtained by fanning an outer layer (2) from a thermoplastic resin having a melting point of 190-300° C. and fonning an inner layer (3) from a thermoplastic resin having a melting point of 150-300° C. and low liquid or gas permeability. The thermoplastic resin that forms the outer layer (2) is preferably a resin having a hoop stress of 10 MPa or greater in a 120° C. atmosphere. Furthermore, the thermoplastic resin that forms the inner layer (3) is preferably a resin having a gasoline permeability of 1.0 g/m2·day or less.

Abstract: A fluid swivel for allowing fluid transfer across a rotary interface between the end of a fluid line connected to the seabed and product piping on a vessel for gas and oil production, wherein the swivel comprises an first annular wall and an second annular which are located with their adjacent cylindrical surfaces in close proximity, the first wall and the second wall defining a chamber, between their peripheral opposing faces, for receiving a fluid, wherein the first wall is adapted to be connected to the end of the fluid line, which extends through the first wall towards the chamber, in order to allow fluid supply towards the chamber and wherein the second annular wall of the swivel is adapted to be connected to the product piping and is provided with a duct to transport the fluid from the chamber towards the product piping, wherein at least part of the swivel comprises a fibre reinforced polymer.

Abstract: An internally insulated rigid exhaust system conduit and method for making the same are provided. The conduit includes an outer rigid tube, a generally flexible inner portion positioned within the outer tube and an insulation layer positioned therebetween. The conduit may include one or more bends or curves. Due to the flexibility of the inner portion and insulation, a gap defined between the inner portion and outer tube may be generally uniform in width even after the bending of the outer tube. During the manufacturing process, the inner portion is wrapped with a blanket or sleeve of insulation material to form a wrapped subassembly and then inserted into the outer tube. The insertion of the wrapped subassembly may occur either before or after a bending of the outer tube. The insulation may also be blown into the gap defined between the inner portion and outer tube.

Abstract: A hose assembly includes an inner tube and an outer cover wrapping around the inner tube. The inner tube has a plurality of inner ribs disposed on an interior surface thereof, a plurality of outer ribs disposed on an exterior surface thereof and a plurality of orifices defined therethrough. The inner ribs and the outer ribs are longitudinally or spirally extended on the surfaces of the inner tube. The outer cover is sewed to form a seam. The seam includes a plurality of holes allowing water to pass through. The outer cover is made of a water-resistant material. Therefore, the water flowing in the inner tube passes through the orifices of the inner tube and the holes of the seam to water the plants.

Abstract: A storage bag for perishable articles includes an unperforated outer layer, an unperforated inner layer, and an intermediate layer disposed between the outer and inner layers. The intermediate layers includes a solventless adhesive mixed with a volatile antimicrobial. In addition, the outer and inner layers are oxygen permeable, and the inner layer has a greater permeability than the outer layer.

Abstract: Methods of reel-laying a mechanically lined pipe (MLP) are described. These include the steps of: spooling the MLP (12) onto a reel (10) in the complete or substantial absence of internal pressure above ambient pressure in the MLP; spooling off the MLP from the reel; aligning and straightening the spooled off MLP, in the complete or substantial absence of internal pressure above ambient pressure, to provide an MLP for laying; and/or the steps of: spooling the MLP (12) onto a reel (10) resulting in the formation of wrinkles in the spooled MLP; spooling off the MLP from the reel; aligning and straightening the unspooled MLP to provide an MLP for laying having wrinkles <4 mm high, removing wrinkles, if any, whilst performing the hydrotest which is used to check fluid tightness of the line.

Abstract: An insulated hose for a high voltage paint application apparatus including an inner hose containing a fluid or paint charged at a high voltage. The flexible inner tube hose is arranged inside at least one flexible mechanical protection tube or layer and an air excluding medium is enclosed between flexible inner tube and first flexible mechanical protection layer. A mechanical protection layer may be surrounded by an electrical protection layer which is grounded. A system for applying paint or other fluid materials at a high voltage is also described.

Abstract: Provided is a steel sheet for manufacturing a pipe having corrosion resistance against fuel vapor of fuel such as gasoline, light oil, bioethanol or bio-diesel fuel, and a pipe and a fuel supply pipe. In the steel sheet for manufacturing a pipe, a Fe—Ni diffusion layer and a softened Ni layer which is provided on the Fe—Ni diffusion layer are formed on a surface of a steel sheet, and a thickness of the softened Ni layer is set to a value which falls within a range of 0.9 to 8.1 ?m thus having corrosion resistance against fuel vapor. In the pipe and the fuel supply pipe, a Fe—Ni diffusion layer and a softened Ni layer which is provided on the Fe—Ni diffusion layer are formed on an inner surface of a pipe formed of a steel sheet, and a thickness of the softened Ni layer is set to a value which falls within a range of 0.9 to 8.1 ?m.

Abstract: Systems and methods for onsite manufacture of a composite pipeline. In one embodiment, a method for constructing a pipeline includes arranging a plurality of sections of tubing at or near to a location where the pipeline is to be finally installed. An end of a first of the sections of tubing axially abuts an end of a second of the sections of tubing. The abutting ends of the first and second of the sections of tubing are joined. A continuous strip of material is wrapped in a helical pattern over the length of the joined first and second of the sections of tubing to form a pipeline segment.

Abstract: The present invention provides conduit assemblies of substantial length that have an inner member disposed in an opening of a conduit member and connected to the interior of the conduit member. The inner member can serve to protect sensitive measuring equipment, such as optical sensors or well logging equipment, from damages, including damages incurred during deployment into subsurface environments, including oil and gas wells and oceans, while allowing for improved data collection by the equipment once deployed. The conduit assemblies can be deployed permanently or as intervention logging equipment. The present disclosure also provides for methods of making and using such conduit assemblies.

Abstract: An adjustable jacket for an insulated conduit is provided, the adjustable includes inner and outer surface, first and second axial ends, and first and second longitudinal ends that each extends between the first and second axial ends. The first and second longitudinal ends form a longitudinal seal, which includes an outer seal formed by a terminal edge of one of the first and second longitudinal ends in contact with the outer surface of the adjustable jacket, and an inner seal formed by a terminal edge of another one of the first and second longitudinal ends in contact with the inner surface of the adjustable jacket.

Abstract: Disclosed are a double water pipe manufactured via hydroforming and a method of manufacturing the same via hydroforming The method includes (a) inserting an inner pipe into an outer pipe made of steel, the inner pipe being made of a corrosion resistant material selected from among stainless steel, titanium and aluminum, and having a smaller outer diameter than an inner diameter of the outer pipe; (b) placing the outer pipe on a die unit and sealing opposite ends of the die unit with sealing members each having a through-hole connected to a fluid supply unit for supplying a fluid to the inner pipe; (c) supplying the fluid to the inner pipe to perform plastic expansion of the inner pipe and elastic expansion of the outer pipe; and (d) discharging the fluid from the inner pipe to allow frictional coupling between the inner pipe and the outer pipe through elastic restoration of the outer pipe.

Abstract: A system and method is described generally for providing a high altitude conduit the high altitude conduit includes a first material layer forming an elongated duct. The high altitude conduit also includes a second material layer outside the first material layer. The second material layer defines a space between the second material layer and the first material layer. A gas has a density that is less dense than that of the atmosphere outside of the second material layer. The gas is disposed in the space between the first and the second layer. An introducer is configured to provide the gas into the space between the first material layer and the second material layer. The gas causes the conduit to extend in an approximately upright orientation.

Abstract: A heat resistant air hose which is excellent in oil-bleeding resistance and causes reduced vibration noise is provided. The heat resistant air hose has an inner layer formed of an inner layer material comprising silicone rubber as a major component thereof; and an outer layer provided on an outer periphery of the inner layer and formed of an outer layer material comprising acrylic rubber as a major component thereof, and the acrylic rubber contains not less than 50 wt % of ethyl acrylate and has a dissipation factor (tan ?) of not less than 0.09 at 150 ° C. and a storage elastic modulus (E?) of not less than 7.0 MPa.

Abstract: A refrigerant line for carrying a mixture of refrigerant and lubrication oil. The line includes an inner casing made of a material impermeable to the refrigerant/oil mixture, an outer casing made of a material that is highly permeable to the refrigerant in its gaseous state, and an intermediate layer between the inner and outer casings made of a material that is high permeable to the gaseous refrigerant but that is able to retain the admixed oil. In this way, any oil contained in a refrigerant/oil mixture leaking through the inner casing is retained by the intermediate layer, while the refrigerant gas is allowed to escape through the outer two layers. The intermediate layer may retain the oil by absorption, by adsorption, or by binding of the oil.

Abstract: The invention refers to a charge air hose for motor vehicles, comprising: a hose-shaped base member and a textile reinforcement. In a conventional charge air hose the textile reinforcement is embedded into the base member or it is arranged between two layers of the base member. A continuing dynamic load of the conventional charge air hose leads to delamination of the composite. To solve the problems known from the prior art, the invention provides a charge air hose for motor vehicles, comprising: a hose-shaped base member, a textile reinforcement arranged on the surface of the base member, wherein the hose-shaped base member is a vulcanized, elastomer-containing hose.

Abstract: Flexible pipe body, a method of manufacturing flexible pipe body and a method of providing a flexible pipe are disclosed. The flexible pipe body includes a fluid retaining layer, at least one tensile armor layer, at least one extruded thermal insulation layer over an outermost one of the at least one tensile armor layers and an outer shield layer over the insulation layer.

Abstract: Multi-layered co-extruded tubes are provided that include an outer layer including a first semiaromatic semicrystalline polyamide having a melt temperature of about 240° C. to 280° C., and a thermal stabilizer; and an inner layer including a second semiaromatic semicrystalline polyamide having a glass transition equal to or greater than 100° C.

Abstract: Multilayer structure comprising at least one couple (L1-L2) of adjacent layers (L1) and (L2), wherein: the layer (L1) comprises at least one polymer composition (C1) comprising: (i) at least one semi-aromatic polyamide, and (ii) at least one impact modifier (I1); the layer (L2) comprises at least one polymer composition (C2) comprising: (i) at least one un-functionalized polyolefin (PO2); (ii) at least one functionalized polyolefin (FPO2), the functionalized polyolefin comprising functional groups chosen from carboxylic groups, their esters, their anhydrides and their salts. Process for manufacturing such multilayer structure, which comprises co-extruding or co-blowmolding polymer compositions (C1) and (C2) so as to obtain one couple (L1-L2) of adjacent layers (L1) and (L2). Shaped article comprising such multilayer structure and process for manufacturing the shaped article.

Abstract: Pressure cast lined steel pipes comprise an annular concrete or mortar liner along an inside diameter, and a metal shell surrounding the liner, wherein the liner is in direct contact with the metal shell. The wall thickness of the liner can be from 10 to 50 times the thickness of the metal shell. The pipe may be coated with a dielectric material. A mold assembly used to form the pipe includes an annular concrete or mortar composition chamber formed between the metal shell and an inner mold member. Pressurized water is used in the mold assembly to pressurize the concrete or mortar composition and exert a desired pressure force onto the metal shell while the composition cures in the mold. Once a desired degree of cure is achieved, the pressure is removed causing the metal shell to exert a desired compression force onto the cured liner.

Abstract: The present teachings provide a detection cell for a biological material and methods for detecting biological material including a photosensitive material optically coupled to an interior volume containing the biological material so to avoid optical components or an external light source.

Abstract: A pipeline comprising an outer steel pipe and an internal corrosion resistant covering adhesively joined to the inside of the steel pipe. The pipeline can be taken up onto a drum and later unwound and laid out without any observed deformation of the metal covering. A method for the manufacturing of the pipeline comprises the steps of applying an adhesive onto the outside of the metal covering and optionally also onto the inside of the steel pipe, inserting the metal covering into the pipe and expanding the covering until being in a good contact with the inside of the steel pipe, and curing the adhesive to make the metal covering adhere tightly to the inside of the steel pipe.

Abstract: A vehicle exhaust component includes an outer shell defining an internal cavity and at least one internal pipe located within the internal cavity. A wire tube surrounds the internal pipe and is spaced apart from the pipe by a radial gap. This radial gap is filled with a fiber material.

Abstract: A spoolable pipe is disclosed, the spoolable pipe having an internal pressure barrier formed about a longitudinal axis, and a reinforcing layer(s) enclosing the internal pressure barrier that includes a solid hydrocarbon matrix. The pipe can also include an energy conductor(s) integrated with and/or located between the internal pressure barrier and/or the reinforcing layer(s).

Abstract: A water pipe structure includes an inner water pipe, and a protective layer mounted on and combined with the inner water pipe to cover an outer periphery of the inner water pipe. The inner water pipe has an outer side provided with at least one extension wing which extends outwardly from the inner water pipe. Thus, the protective layer encompasses the outer periphery of the inner water pipe to protect the inner water pipe.

Abstract: In one aspect of the present invention, an external tubular member comprises an external outside surface and an external inside surface joined by an external wall thickness. The external wall thickness comprises external sintered polycrystalline diamond. An internal member comprises an internal outside surface and an internal width. The internal width comprises internal sintered polycrystalline diamond. The external inside surface is adjacent to the internal outside surface.

Abstract: Provided is duct equipment including a duct body, a heat insulating material, a external cover, a fiber-reinforced sheet, and fiber-reinforced moldings. The duct body includes a duct wall, a duct passage defined by the duct wall, and duct corners formed in the duct wall when viewed in a cross-section in a direction intersecting a direction in which the duct passage extends. The heat insulating material is installed on an outer circumference of the duct body. The external cover includes a external cover wall installed on an outer circumference of the heat insulating material, and external cover corners formed alone the duct corners. The fiber-reinforced sheet is disposed on the outer circumference of the duct body via an adhesive layer. The fiber-reinforced moldings are disposed adjacent to the fiber-reinforced sheet along the external cover corners via adhesive layers, and have a substantially L-shape when viewed in the cross-section.

Abstract: A drain pipe coupling for connecting a primary pipe having a primary width ?1 to two or more secondary pipes, said secondary pipes having a secondary width shorter than the primary width of the primary pipe, said drain pipe coupling having a cuff for connecting to the primary pipe and a transition portion connecting to the secondary openings; a downspout extension terminating in a collapsible, extendable and flexible low profile corrugated discharge pipe having a substantially symmetrical oblong cross section but not having any internal supports; a reducing insert adapter for connecting a 2 inch rectangular downspout to a 4 inch rectangular cuff comprising a first open adapter-end sized to engage with the rectangular cuff and a second open adapter-end sized to engage with the open end of said second rectangular gravity-flow drain pipe; and a gravity-flow drain pipe having a camouflage pattern displayed on a portion of the outer surface of the pipe.

Abstract: The invention relates to a plastic molded pipe, in particular for fuel-conducting return lines in injection systems for internal combustion engines. The plastic molded pipe has an inner pipe and an outer encapsulation made of a plastic material with connectors for additional components of the fuel injection system. The inner pipe is embodied as a plastic inner pipe with at least one bend.

Abstract: A laying pipe configured for rotation about its axis in a rolling mill laying head, comprises a ferrous outer tube having an entry section aligned with its axis, an intermediate section curving away from its axis, and a delivery section having a constant radius measured from its axis. A ferrous inner tube has entry, intermediate and delivery sections respectively lining the entry, intermediate and delivery sections of the outer tube. The inner tube is constrained against movement relative to the outer tube solely by frictional contact with the outer tube. The inner tube is movable incrementally within the outer tube in one direction in response to heating and cooling cycles during rotation of the laying pipe about its axis.

Abstract: A flexible hose for conveying fluids and suitable for high temperature environments, in one embodiment the hose assembly comprises a thermal paint coated nipple, a core tube, a thermal insulating layer surrounding the core tube, a cover layer surrounding the thermal insulating layer, and a vented jacket surrounding the cover layer. The thermal insulating layer may be a fibrous material such as a silica fiber. The cover layer may be thermally stable up to 750° F. or higher. The vented jacket may be a wire braid having interstices therein and formed from a corrosion resistant material.

Abstract: A method of forming a slotted liner, having a wall comprising a plurality of non-axial bending members axially separated by non-axial slots and circumferentially interspersed with bases, for providing strain relief, the method comprising: forming the bending members and the non-axial slots by one of: cutting non-axial slots, and winding a rod; configuring the circumferential lengths of the plurality of non-axial slots and bases relative to the liner circumference; wherein positioning a first base axially adjacent to a non-axial slot; configuring the non-axial slot circumferential length longer than the circumferential length of the first base; and positioning a second base axially adjacent to a first base; providing connections between the pair of bases or leaving uncut the wall between the base pair; configuring the plurality of non-axial slots and adjacent base pairs.

Abstract: A tubular structure having a multi-layer, strength-enhanced first end segment, a multi-layer, strength-enhanced second end segment, and a flexible segment intermediate said multi-layer strength-enhanced first end segment and said multi-layer, strength-enhanced second end segment is provided. Methods for manufacturing tubular structures are also provided.

Abstract: Disclosed is a pipe resin composition. The composition comprises a polyethylene pipe resin, a primary antioxidant, and an acid. The composition of the invention has an increased oxidative induction time (OIT) and environmental stress cracking resistance (ESCR).

Abstract: A multilayer tube for an automatic transmission, the multilayer tube comprising at least one layer of elastomeric material resistant to oils, in particular to DEXRON VI. Advantageously, the layer of elastomeric material is a mixture of CSM (polyethylene chlorosulphonate) and EVM in which the percentage ratio between EVM and CSM is comprised between 4:1 and 1:1.

Abstract: A biocompatible tube that can be used in a liquid chromatography system is described. The tube can have flanged or straight ends, and can be used in conjunction with one or more fitting, assembly.

Abstract: The invention provides a pipe 100 for an aircraft refuel system, the pipe comprising an outer section 200 making up a pipe wall, the pipe wall having an outer and inner 230 surface, a surface texture 310 on the inner pipe wall surface, the surface texture comprising projections 311 projecting inwards from the inner pipe wall surface towards the centre of the pipe. The surface texture may be riblets 311 and may be coated with an anti-bacterial coating 340. The surface texture may be formed from a layer of conductive material, in the form of a foil 300. The outer section 200 may be made from a non-conductive, preferably composite material. The invention also provides a method of manufacturing piping for an aircraft refuel system using a mandrel 400.

Abstract: A pipe for underwater transportation of fluid is indicated which includes a pressure-tight metal inner pipe for conducting the fluid, wherein for its stabilization in radial direction at least one profiled metal strand and for stabilizing in the axial direction at least one tension-proof strand are wound around the inner pipe. The inner pipe (1) is a metal pipe which is undulated transversely of its longitudinal direction and which for stabilization in the radial direction is surrounded by at least one first radial reinforcement (3) which is composed of a profiled helically extending profile strip whose windings are placed closely next to each other or engage each other and are hooked together. Arranged around the first radial reinforcement (3) is arranged a metal pipe undulated transversely of its longitudinal direction as the outer pipe (5); at least two layers of tension-proof strands (7, 8) are wound around the outer pipe (5), preferably with oppositely directed pitch.