Pump impeller screw needed?

[RocKKer]

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.

 

[Durk]

I just swapped in a two-speed motor on the same pump you have. I got my gaskets/seals from http://www.poolpartsonline.com/p-84570-pentair-whisperflo-whisperflow-pump-parts.aspx. This paragraph on the WhisperFlo part page may reassure you. For the record, my new motor shaft WAS threaded and I did use the screw.

** Please Note **
Replacement motors may or may not come with the shaft internally threaded as the original OEM motor. It is not a requirement for replacement motors. Replacement motors are copies of OEM designs and the tapped hole exists only because OEM customer requested it. Since certain replacement motors have been released having this feature, some customers have come to expect it assuming that the threads are necessary or there will be a problem with the impeller coming off. This is not a correct assumption. AO Smith has built replacement motors without the threaded holes for over thirty years and is not aware of any case where the impeller has spun off. If the lack of a threaded hole remains a concern, they suggest using Loc-tite or a similar product to alleviate the concern.

Since I assume the pump was operating with no head on the screw for some time, that might reinforce the argument that the screw is indeed unnecessary.

 

[RocKKer]

Wow, surprisingly the pool store got it right!

I'll put it back together without the screw, don't think I'll Loc-tite, it' hard enough to unscrew by hand as it is.

Thanks Durk!

 

[RocKKer]

Got it all back together, no leaks, no unscrewed impeller - powered on and off 4 or 5 times to test. Next time I'm thinking if I have the screw I'll use it, if not I won't worry about it.

 

[JamesW]

Pretty much, the only time the impeller can unscrew is if the impeller is forced backward, such as by compressed air in a filter decompressing when the pump is turned off, and forcing water backwards through the pump. If you have a check valve after the pump, and/or minimum air in the filter, the water is unlikely to be forced backwards.

The primary time that it is an issue for most people is when they start the pump after opening the pump lid and then shut the pump off right away. That's because the trapped air from opening the pump does not have time to be bled off by the filter's internal air relief valve.

You can bleed off air from the filter using the manual air bleed valve before turning off the pump. If air is constantly introduced, then it would indicate a suction side air leak that should be addressed.

Also, note that the screw is a left-handed thread and loosens in a clockwise direction.

 

[MitchRyan912]

If the impeller you have has a thru hole, does anything need to be done to seal it up so water doesn't come through the hole?