There is also a switch to run the transformer. Most companies are quickly moving away from the ignitron tube firing because of environmental concerns and accuracy. Ignitron tubes date to the 1930's. SCR's were introduced in the early 1960's. Both units are water cooled.
Controls can get very complicated.
They may be able to run multiple valves and multiple transformers from one control. Many models are capable of interfacing with PLC's and PC's. The principle of the transformer is based on Electromagnetic Induction and was discovered in 1831. The transformer consists of a primary winding, secondary winding, and a magnetic core, onto which the two windings are placed. Without getting into the physics involved, as a voltage and current are applied to the primary winding, a subsequent voltage and current is induced in the secondary winding.