The basic working principle of a vacuum tube is a phenomenon called thermionic emission. It works like this: you heat up a metal, and the thermal energy knocks some electrons loose. ... When the cathode is heated, and a positive voltage is applied to the anode, electrons can flow from the cathode to the anode.

How does a electronic valve work?

Solenoid valve is a control units which, when electrically energized or de-energized, either shut off or allow fluid flow. The actuator takes the form of an electromagnet. When energized, a magnetic field builds up which pulls a plunger or pivoted armature against the action of a spring.

What is meant by thermionic valve?

thermionic valve in British English

or especially US and Canadian thermionic tube. noun. an electronic valve in which electrons are emitted from a heated rather than a cold cathode. Collins English Dictionary.