"Valvo was an old and renowned german company.
Before 1914 the company "C.H.F. Mueller GmbH Hamburg" produced only X-ray tubes (therefore, they were known as "Roentgen-Mueller"). After 1916, probably triggered by the requirements of WW-I, "ordinary" tubes (mainly Xmitting ones) were added
to the program.
In april 1924 Mueller created a daughter-firm called "Radio-Roehren-Fabrik GmbH" or just "RRF GmbH" (meaning radio-tube factory); they took over the tube-production from Mueller.
In 1926 RRF was renamed to "VALVO". that name was inspired by the latin word "valvae" (something like door wing, to symbolize the flow-control of electrons), plus the english "valve". since then VALVO used their typical logo, a sort of jagged ring with a stylized "VALVO" written inside, which was kept (almost) unchanged for more than 5 decades.
In 1927 Philips bought C.H.F. Mueller (Mueller had financial problems), and later in 1932 also VALVO (Mullard became a Philips-daughter, too).
VALVO didn't just produce tubes (incl. camera/pencil/Geiger/PM types, & up to 1 MW klystrons), but a whole lot of other stuff like ceramic caps, piezo-elements, ferrites, smaller motors, transformers, deflection-yokes and (b/w + color) picture-tubes, diodes, transistors, loudspeakers, etc."
From Herbert, Vacuum TUBE INFO Junction