A valve is a device for controlling the passage of liquids and gases through pipes and other channels. Automatic valves, operated by the fluid itself, include pump valves of all kinds, safety-valves, and reducing valves. Mechanically operated valves, the movements of which have a definite time-relation to the movements of other parts, independently of the fluid, are used in hydraulic, steam, gas, and oil engines to govern the admission of the working fluid to the cylinders and its expulsion therefrom. Stop-valves, regulating valves, etc, are worked directly or indirectly by hand.
In electronics, a valve is a device consisting of two or more metal plates enclosed in an evacuated glassbulb. One of the metal plates is heated, causing electrons to be emitted. If a positive charge is applied to the other plate, the electrons will move towards it and the valve will conduct electricity. Valves have largely been superseded by transistors which are smaller. Research Valve
Abbreviations
SciTech
Research Valve