This analogy goes pretty deep. Fun fact, in British English the term for a vacuum tube triode is "valve" precisely because it operates like a valve. FETs (part

This analogy goes pretty deep. Fun fact, in British English the term for a vacuum tube triode is "valve" precisely because it operates like a valve. FETs (particularly JFETs) follow the same analogy (which is why FET and triode amplifier circuits look basically the same) using the field effect instead of thermionic emission.