Valve

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.

Valves have many uses, including controlling water for irrigation, industrial uses for controlling processes, residential uses such as on / off and pressure control to dish and clothes washers and taps in the home. Even aerosols have a tiny valve built in. Valves are also used in the military and transport sectors.

Vacuum tube

In electronics, a vacuum tube, an electron tube, or just a tube (North America), or valve (Britain and some other regions) is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament. This type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect. Not all electronic circuit valves/electron tubes are vacuum tubes (evacuated); gas-filled tubes are similar devices containing a gas, typically at low pressure, which exploit phenomena related to electric discharge in gases, usually without a heater.

The simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode (the filament itself acts as the cathode in some diodes), and a plate (anode). Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the cathode travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids. Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display.

Valve Corporation

Valve Corporation (also known as Valve Software, commonly referred to as Valve) is an American video game developer and digital distribution company headquartered in Bellevue, Washington, United States. Its Luxembourg-based business office subsidiary for European regions, Valve S.à r.l., was opened in 2012. Founded in 1996 as Valve L.L.C. by former Microsoft employees Gabe Newell and Mike Harrington, the company has developed the critically acclaimed Half-Life, Counter-Strike, Portal, Day of Defeat, Team Fortress, Left 4 Dead video game series, alongside Dota 2. It also developed and maintains Source on which most of its games run, and the software distribution platform Steam, which has led to the Steam Machine, a line of pre-built gaming computers running SteamOS.

History

Founding and incorporation

Valve was founded by former longtime Microsoft employees Gabe Newell and Mike Harrington on August 24, 1996, as Valve L.L.C., based in Kirkland, Washington on the Seattle Eastside. After incorporation in April 2003, it moved from its original location to Bellevue, Washington, the same city in which their original publisher, Sierra On-Line, Inc., was based.