Did the articulated Steam Engines have 'dual throttles'?

I was about to answer ONE boiler, on an articulated frame, until I read the previous answers from Joseph, who states TWO boilers, and Derail, who states ONE boiler. I have always understood single boiler units on articulated frameworks. Never have I really seen or know of TWO boilers on a single unit. Not really sure if it would be safe or even practicle. Anyway, my vote goes to Derail with ONE boiler. My opinion and knowledge is limited to ONE boiler.