I took my Whipserflo wfe-4 filter pump apart to change a leaky seal, earlier this year it had run while half full due to leakage issues which have been fixed. To my surprise I found the impeller screw head was missing! Looked it had boiled away, all that was left was a point where the head had been. I assume this means that the cavitation from running it half full caused the steel screw to dissolve, only heard about things like that never experienced it.
The real question is, I went the pool store to get a replacement screw they said that screw is used to prevent the impeller from unscrewing and "they" found that the unscrewing of the impeller didn't occur, so today's pumps don't even have them.
I am inclined to replace it anyway, but it might be several days before I can get one in, I am also inclined to put it back together without the impeller screw (and keep an eye on it) so I am not down.
So is this impeller screw needed and am I risking disaster by re-assembling without it?
Edit - added pic of impeller screw, the pointy end is where the philips head used to be.