YEA
It’s an optional air intake water or dust separator.
If you can still access the truck it should show on the SPID label.
K
Yeah, yeah he nailed it. It's a preliminary air separator used as part of the RPO K46 option (air cleaner, heavy duty, pre-cleaner).
It is essentially a cyclonic type air filter/separator. The bladed disc doesn't spin. It is designed to impart a centrifugal force to the incoming air flow as it passes through the blades. Any moisture/particulates that are entrained in the combustion air get flung out to the ID of the pipe and drop down into that hopper shown in the last picture. That pointy looking thing under the hopper is called...IDK...the purge valve maybe. It is rubber and has a slit at the bottom. When enough stuff falls down into the hopper, something (again IDK, maybe the weight of the junk or an increase in air flow across the blades). The slit in the boot opens and purges some of it.
The engineers really love these because the never get clogged - like a paper filter. And perhaps more importantly; due to the fact that they never get clogged up - even in harsh environments - combustion air flow is always unrestricted.
That's all I know - or can remember anyway. Oh yeah, I believe they were first used in tanks during WWII.