Marc, Welcome to Stovebolt
The red cast housing is the fire pump primer pump/controller. It's job is to allow truck engine vacuum to be used to purge the air out of the suction side of the main pump as well as the draft hoses. The controller has a float assembly that prevents pond water from being sucked into the engine once the pond water reaches the main pump...just like a carburetor float/needle seat valve. New fire engines use electrically driven primer pumps as diesel engines don't make vacuum, so all that stuff is obsolete now.
Like John said, you can/should remove all of that to clean up the engine bay...I'm sure there is someone in the world that would take that stuff off your hands, but it's probably not worth what it would cost to ship it.