DE Blowing out of returns when filter is turned on

  • Last Post 05 December 2021
FrankTu posted this 18 May 2018

I have a Hayward DE 4800 filter. The filter started up perfectly normal this year. I loaded it with DE and everything was working fine and shocked the pool to kill algae and clear the water. After a day of filtering, as would be expected, the pressure went up since the filter was cleaning rather dirty water...normal stuff that happens every year. The filter shut off due to the timing cycle. Here is where the trouble started. I turned the filter on and noticed that a bunch of dirty DE came blowing out of the returns. Alarmed, I shut it down. After some research, I decided to just replace the entire set of grids including the manifold since they were very old (I bought the whole assembly). During the replacement, I also inspected the the outlet elbow piping, which looked completely fine and replaced the o ring that is on that piping that the manifold goes onto. I also took apart the multiport valve to check the gasget and it looked fine. I have no air or water leaks in the system (i.e., the DE is not draining back through the supply lines when I shut the filter). I put everything back together and loaded up the DE and everything again seemed fine (DE loaded properly, nothing came out, same as original start up). Unfortunately, the same exact thing happened the next day. After the filter was off for awhile, I turned it on and dirty DE came blowing out of the returns. I backwashed the system to clear out the DE and reloaded it. It loaded fine. I ran the filter for about an hour and then shut it for about an hour. This time it restarted fine (no DE blowing out of returns). Sorry for long story, but wanted to cover everything. It seems to me that after the filter gets dirty, something is going on where at the moment it is turned back on after being off a little while DE is making its way into the return path somehow. Could it be some kind of back pressure event due to the filter being dirty? I've run this sytem for 15 years, had plenty of dirty filters that I turned on before I got a chance to backwash, never had an issue. Is it possible that a defect that I am not seeing in the multiport valve, coupled with the back pressure due to it being dirty is causing this? Or perhaps the pressure is causing the the dirty DE to push past the o-ring on the outlet piping? Please let me know if you guys have encountered something like this and/or if yuo have any ideas as to what it might be. Thanks in advance.


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joewdunbar posted this 04 June 2021

I have the same problem, my filter, a Pentair FNS Plus 48 DE, runs fine at first, and then when the pressure gets high, around 30 or so, it starts blowing DE back out into the pool. When I start with a clean filter the pressure is around 14-15, then I let it reach 30 before I backwash.

Perhaps I need to backwash before the filter reaches 30? Anyone else experience this? Could it be something else and not the high pressure?

Orionthelab posted this 05 June 2021

Here are a few articles that might help your guys...


How To Prevent DE Filter Powder Returning to Pool

Getting DE Powder in Your Pool?

Phoeniix posted this 05 December 2021

Thank you, after reviewing the articles referenced, I am fairly certain my culpret is the Spider gasket. The pool shops ALL told me it was NOT the valve but... I have replaced the Manifold, all the grids, filter gaskets etc. nothing else is left and I have the same symptoms when I try to vacuum the DE off the bottom of the pool (Which of course raises the system pressure).

I have no leaks to the waste line or water drips.

I did switch to waste mode once with the pump on, b ut this issue did not show up until later.

I hope this is helpful to someone, don't assume the pool shop is always right!

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