Spring Loaded Vanes?

[AmericanPreferred]

I have had a few air tools apart, got most of them back together working, but have not encountered a spring loaded motor so far. I don't know if I could reassemble this one should I ever take it apart. What is the purpose of the vane springs? I have looked at several parts diagrams, and so far this is the only one with springs under the vanes. The ipl is at the bottom of the page. Part#27

http://www.northerntool.com/images/downloads/manuals/100803.pdf