Pool pump lost prime

I just replaced the big O-ring gasket on my Hayward ec-75 Perflex filter. The leaks have stopped but now my water flow slows down after an hour or so (checking the strainer basket on pump) I have to stop the pump (newer Hayward) and restart which usually works for another hour or so. Is there anything on the filter that I could have affected that woud cause this behavior?

What is curious is if I open the filter drain valve when its running low the water flow spikes throught the pump and flows like it used to. The filter is clean (I opened and cleaned when chnaged O-ring). Is there anything on the filter that would cause this?

Unfortunately, as common as they are in some parts of the country, I've never even seen a Perflex, much less worked on one. I gather from what I've heard, and from the parts diagram, that they are very 'twitchy' filters, and rather easy to mess up when disassembled and re-assembled.

It almost sounds like something is causing your filter to rapidly clog up. I'm going to guess -- and it's only a guess -- that you made an error in re-assembling the pump, that is causing it to perform incorrectly. If I understand what you are saying about the drain valve, the pump can operate normally, when you open the valve, removing the restriction.

If your pressure gauge is working, it *should* reveal if I'm correct in my guess. But again, it's not clear in the parts diagram I looked at, exactly where in the water flow the gauge is located. So I can't be sure.

I dis-assembled my filter (again) and checked the EC-75 diagram. Seems that there is a O-ring (O-30) missing on the top end of the bump rod. Could that be the culprit?

FYI - Not O-Ring - it was there but was small and recessed so didn't see it at first. Problem was crack in top plate where bump rod goes through. Replaced plate and fine now. Only hassle was that on that model you have to manually take out all DE "fingers" and replace on the new plate which took some time. Thanks for reply.

Sorry, no one could help you more, but glad you were able to work it out.

And, yes, messing around with all the fingers is notoriously one of the not-well-liked aspects of that filter. Seems to work pretty well, though, so long as you are not having to work on it!