Plastic pipe is a tubular section, or hollow cylinder, made of plastic.It is usually, but not necessarily, of circular cross-section, used mainly to convey substances which can flow ? liquids and gases (fluids), slurries, powders and masses of small solids.It can also be used for structural applications; hollow pipe is far stiffer per unit weight than solid members. There are three basic types of plastic pipes: Solid wall pipe Extruded pipes consisting of one layer of a homogeneous matrix of thermoplastic material which is ready for use in a pipeline Structured wall pipe Structured-wall pipes and fittings are products which have an optimized design with regard to material usage to achieve the physical, mechanical and performance requirements.Structured Wall Pipes are tailor made solutions of piping systems, for a variety of applications and in most cases developed in cooperation with users Barrier pipe Pipe incorporating a flexible metallic layer as the middle of three bonded layers.Barrier pipe is used, for example, to provide additional protection for the contents passing through the pipe (particularly drinking water) from aggressive chemicals or other pollution when laid in ground contaminated by previous use. Most plastic pipe systems are made from thermoplastic materials.The production method involves melting the material, shaping and then cooling. Pipes are normally produced by extrusion.Źródło: https://en.wikipedia.org/wiki/Plastic_pipe
A union is similar to a coupling, except it is designed to allow quick and convenient disconnection of pipes for maintenance or fixture replacement.
Pipe unions are essentially a type of flange connector, as discussed further below. In addition to standard, simple unions, other types of union exist: Dielectric unions are unions with dielectric insulation, used to separate dissimilar metals (such as copper and galvanized steel) to avoid the damaging effects of galvanic corrosion.
When two dissimilar metals are in contact with an electrically conductive solution (even tap water is conductive), they will form a battery and generate a voltage by electrolysis.When the two metals are in direct contact with each other, the electric current from one metal to the other will cause a movement of ions from one to the other, dissolving one metal and depositing it on the other. A dielectric union breaks the electric current path with a plastic liner between two halves of the union, thus limiting galvanic corrosion. Rotary unions are unions that allow for rotation of one of the united parts.Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting.