It's a lot more physically demanding than most realize. Those throttles are hard to open, and especially hard to open just a bit to get the cylinders to fill just enough that the locomotive nudges forward or backward a tad. They finally had to get power reversers because, as the hoggers were asked to run larger steamers with higher boiler pressures, they were thrown back or forward as they released the ratchet mechanism on the old Johnson Bars. The Pennsy's K4 Pacifics were delivered without stokers if I remember, but they were added later.
A lot of those valves were for opening steam or air lines to clappers on the bell, the steam turret, the turbo-generator, the cross compound air pumps, the feedwater heater, the feedwater pump, the tender cistern heater and fuel oil heaters if they were oil burners, there's valve for the atomizers into the firebox (firing controls and levers), steam valve to the mechanical stoker, and valves to its jets on the distribution plate. There's a valve for the hydrostatic lubricator if their is one. Yeah, it's a busy place. Hot, too. Or just right during the coldest winter months if it's an all-weather cab.