Abstract: A tubular product has a tubular base layer, a tubular innermost layer made of plastic by continuous extrusion, and a tubular tie layer of foamed plastic between and adhered to the base layer and the innermost layer. The tie layer is made of melt processable adhesion plastic, is extruded simultaneously with the innermost layer against the base layer, and has better adhesions to the base and innermost layers than the base and innermost layers have to each other.

Abstract: The invention provides, in a first form, an expandable plug for regulating pressure or flow within a tube. The plug has an inflatable bladder (12) for diametral expansion by internal fluid pressure introduced by inlet (14). The plug is reinforced by an envelope (26) of cords (28) which spread laterally upon inflation of the bladder to provide diametral support to the bladder. In a second form of the invention, an inflatable plug positioned in a tube of internal diameter d is controlled according to the equation P.sub.p =.DELTA.P+P.sub.d wherein P.sub.d is the internal pressure in the plug, .DELTA.P is the differential pressure across the plug and P.sub.d is the plug free expansion pressure for diameter d.

Abstract: A sizing sleeve for controlling the diameter of plastic tube includes pressurized sizing sleeve portions in which fluid is injected under pressure about the tube circumference to form a lubricating layer. Drainage zones axially separate and isolate adjacent pressurized portions to allow independent temperature and pressure control. Each pressurized portion has flow stabilizer reducing variations in flow responsive to changes in the lubricating layer pressure. The flow stabilizer may comprise a high pressure fluid source and high pressure drop constrictor comprising fine apertures, which may be formed as grooves milled into end surface of abutting sizing sleeve segments.

Abstract: The invention relates to a method for manufacturing a multi-layer corrugated pipe and to a corrugated pipe manufactured by the method and comprising an inner tube (2), a corrugated outer tube (5) and a plastic layer therebetween. Separate layers (3,6) of plastic are formed on the outer surface of the inner tube (2) and the inner surface of the outer tube (5), said separate layers of plastic being affixed to one another at least at the web portions (5a) of the corrugations of the outer tube (5) when the inner tube and outer tube are connected.

Abstract: A method of socketing a pipe of oriented plastic having an annular groove inside the socket. An end portion (15) of the pipe is pushed onto a cylindrical mandrel element (11) and the region (l.sub.1) of the end portion at the opening thereof where the groove is to be located is heated to a temperature above the glass transition temperature of amorphous plastic and the crystalline melting point of crystalline plastic, respectively. The rest of the end portion is maintained at a temperature below the glass transition temperature or the crystalline melting point, respectively. The end portion (15) when said region is at a temperature above the glass transition temperature or the crystalline melting point, respectively, is pushed onto a second mandrel element (13) axially aligned with the first mandrel element the bottom portion of the socket being formed by said second mandrel element (13). The rest of the end portion is expanded to form the bottom portion of the socket.

Abstract: The invention relates to a socket joint for plastic pipes, whereupon a spigot end (1a) of one (1) of the pipes to be connected is inserted in an expanded section (2a) of a socket (2), and an intermediate space (3) situated between the spigot end and the expanded section comprises a housing sealing unit (4) that extends along a considerable part of the length of said intermediate space and that comprises several circular flexible lip seals (6) on its outer and inner circumference. The outer and inner circumference of the sealing unit (4) also comprise several circular support seals (7) which have a substantially smaller compressibility especially in the radial direction than the lip seals (6).

Abstract: An adjustable pipe bend which has at least two parts joined by flanges (10, 10a) which incorporate an electrical fusion element in the form of a plastic annular disc (15) with a heater wire (16) located at or adjacent both surfaces of the disc.A number of embodiments of the invention illustrate different adjustable bends, the arrangement being that the bend is adjusted to a required position and then the heater wire has a voltage applied to it to produce a heating current which causes the plastic annular disc and adjacent plastic faces of the flanges to melt sufficiently to cause fusion between the two parts of the pipe.