What is the purpose of the 8.4" motor?

[blackheart]

I picked up that Canavac XLS from my friend and found that it sounded really rough like the motor was unbalanced. The front fan has been grinding against the fan case which has caused it to wear away. I also found that the fans are only 5" in diameter... and it's like if the fans are so small what is the purpose of making the outer casing so large? It just seems absurd and I have to wonder if the other 8.4" motors are like this too. This one is an Ametek 122175-00

 

[centralvacs1928]

That's a shame about the motor damage. Wonder how it happened. That is normally a very long lasting motor (1500+ hours thanks to extra long curved carbon brushes).

I've wondered the same thing about a smaller fan in a larger casing. Seems like Lamb's earlier, less powerful designs used fans closer in diameter to the housing (5.7" or 7.2"). Later, higher-performance models seemed to use smaller tapered fans, and sometimes one smaller one and a larger one (or two) underneath.

Even big industrial turbine vacuums, like Spencer, often use impellers that seem undersized (or put them in a housing that seems oversized). I'm sure there's a reason. I know the larger diameter impellers can have a lot of vibration if they aren't balanced perfectly.