Turning propellers by hand
I read in the March Pilot magazine that if you do have to move a propeller that you should turn it backwards which is what I advise my students.
However, the article in the magazine continues with a caution that turning a prop backwards can 'shatter the vanes in the vacum pump'.
This is new to me so can anyone offer any more information on this possibility? I have had a thorough look in our PA28 POH and can find no mention of it.