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.
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.
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.
When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow. Elbows are categorized based on various design features as below: Long Radius (LR) Elbows ? radius is 1.5 times the pipe diameter Short Radius (SR) Elbows ? radius is 1.0 times the pipe diameter 90 Degree Elbow ? where change in direction required is 90° 60 Degree Elbow ? where change in direction required is 60° 45 Degree Elbow ? where change in direction required is 45° A 90 degree elbow is also called a "90 bend" or "90 ell".
The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains.These elbows can be made from tough nylon material or NPT thread.Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting
Galvanized steel potable water supply and distribution pipes are commonly found with nominal pipe sizes from 3?8 inch (9.5 mm) to 2 inches (51 mm).
Black lacquered steel pipe is the most widely used pipe material for fire sprinklers and natural gas. Źródło: https://en.wikipedia.org/wiki/Plumbing.