Some of them are contracted by the city authorities and owners of various public buildings, and others by owners of private flats and houses.Therefore, the scope of hydraulic works performed in cities is very wide. It includes both Pip drains and supervising the work performed after the flooding of the city by heavy rains and repair of hydraulic failure in flats and houses and installation of new sanitary facilities. Such an installation can be performed by plumbers working alone or working in the company hydraulic system. While the work is carried out after heavy rains need to rent a large company hydraulic system.
An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made.The ends may be machined for butt welding, threaded (usually female), or socketed, etc.
It is a fitting which is bent in such a way to produce 90 degree change in the direction of flow in the pipe.
These elbows can be made from tough nylon material or NPT thread.Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting
A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure..The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll. The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction.This is called a check valve, as it prevents or "checks" the flow in one direction.
Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems. Źródło: https://en.wikipedia.org/wiki/Valve