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
Gaskets are mechanical seals, usually formed like a ring and used for sealing of flange joints.In general, gaskets should not be reused. Various types of gaskets are available depending upon their construction, materials, and features.
The following are the type of gaskets commonly used: Non-Metallic Gaskets (ASME B 16.21) Spiral-Wound Gaskets (ASME B 16.20) Ring Joint Gaskets (ASME B 16.20) Non-Metallic Gaskets are used with flat face or raised face flanges.
Spiral-Wound Gaskets are used with raised face flanges.
They are available with an inner ring and outer ring, which is also known as the cantering ring.
Ring Joint Gaskets are used with Ring Type Joint (RTJ) flanges.They are available in octagonal or oval cross sections. A very high surface stress is developed between an RTJ gasket and the flange groove when RTJ is bolted up in a flange.
This leads to plastic deformation of the gasket.Thus, the hardness of the gasket is kept less than the hardness of the groove to achieve coining i.e. bringing two metal surfaces of different hardness so tightly together that the softer surface deforms to match harder surface exactly in shape and finish. Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting.