Super Heaters?

Okay, I am still studying up on locomotive interiors, not being around them enough to understand it all clearly. So please be a bit patient with me.
This is what I am seeing so tell me if I am wrong (nicely please). The saturated steam builds up pressure in the boiler, the steam dome has the the highest psi in the boiler because it is a raised surface area in the boiler and heat naturally rises to the highest point. As the throttle is opened the steam rushes down through the dry pipe and into the Superheater in which also it sends it down through smaller pipes that are within the boiler, but not in the same pressure chamber as the main boiler, to be superheated. Then it is gathered and then divided into two pipes going to two different cylinders. There must be a loss of the thermal temperature at this point.
The question at hand is, is the psi a variable or a constant between the dry pipe and the entrance to the steam chest. Are there small valves in place to keep the steam from moving backwards if there were any loss in pressure behind the superheaters or is there a pump in those areas or is it just gaining more psi as the saturated steam is being split and then split again into super charged particles of H2O?

Still a Student, Dave