During centrifugal blower operation, air, or gas, is drawn into the inlet head(casting) whereby  the inlet casting design directs the air into the eye of the first impeller.   The impeller eye actually encircles the shaft, so the air flowing in becomes parallel to the shaft, which is parallel to the ground.

The spinning motion of the impeller then increases the speed of the air flow and directs it straight up to the top of the blower in a perpendicular direction to the shaft/ground.   The design of the cast iron section turns the air flow 180^O and vanes in the section direct the air straight down again to the rotating shaft and the eye of the next impeller.  From the impeller eye, the air is again turned 180^O and forced back up to the top of the blower.  Again increasing its' speed and, in effect, pressurizing it.

The cast iron section can be designed to provide a nice smooth flow to turn the air 180^O at the top of the blower.  But at the bottom 180^O turn, a "baffle ring" is installed around the spinning shaft to keep the air flow smooth and counteract any air turbulence.   The baffle ring, if designed and fitted correctly, eliminates the air turbulence(bubbles), so the space can actually hold more air.

If the blower internals can hold more air, the blower will perform better. So baffle rings simply increase the performance of the blower. Baffle rings are usually nickel or chrome plated to ensure a smooth air flow and thereby increase the air speed(pressure).  A blower with baffle rings will provide more volume(cfm) and pressure(PSI), and will use less HP than a blower without baffle rings.

If you have 2-3 blowers that have to run in parallel together, and they all have baffle rings, you cannot remove the rings from one of the blowers and expect it to run in parallel anymore.  Fro example, on an 8" blower with 6-7 stages, there could be a 200 cfm, .5 PSI difference between the 2 blowers.  You most likely would not be able to bring the blower on line.

Small blowers(below 5" diameter), generally do not have baffle rings.  Some Model blowers(Lamson #870) may not have a baffle ring at the inlet, while some larger blowers(16" - 24"), may have the baffle machined into the inlet casting. At least one manufacturer uses special MBR's(multiple baffle rings) at each cast iron section. 

Baffle rings are held in place with machine screws, that are very prone to rust and corrosion. Replacing the rings almost always involves re-drilling and tapping the cast iron section.  Either all of the sections have baffle rings, or none of them have.

So what is a Baffle Ring? How about calling it an "enhanced performance inducing mechanical device".