DE blowing back via returns

[mjones13]

We presently have two problems going on with our pool. The DE blowing back into the pool is the more important of the two. When the filter turns on, the earth blows very heavily from one return line and a little from the other. It last a 45 seconds or so. This happens when ever the pump is turned off, whether for 8 hours or 5 minutes. We have replaced ALL the grids with unicel grids, we have replaced all O-rings and we have replaced the multiport valve. My husband is ready to buy a new filter (this one is @7 years old), but I thought I'd inquire here before potentially wasting money. There are no visible cracks in the manifold or the outlet elbow. I am thinking of replacing each of them next. What else could it possibly be??
The second problem that I am not worried about right now is a suction side air leak, all gaskets and O-rings again have been replaced and well lubed with Magic Lube. We removed the heat pump from the system which was likely to be 95% of the problem but still not 100% fixed. Right now the DE is the biggest problem. I'd like to fix it before the summer is gone. Thank you for your help.

 

[chiefwej]

Does this happen ever time the pump is turned on or just after you have cleaned the filter?

I once had a similar problem, where just a puff of DE came out every time the pump started. It was solved by replacing a failed check valve between the pump and filter. It was allowing DE to flood back through the pump and fill the suction line, every time the pump was shut down.

 

[BuckeyeChris]

have you tried the multiport in various positions to see if the DE is blown to waste on startup, or anything like that?

 

[Inflatableman1]

The de has to pass through the system to come out of a return. So I think what Chief has mentioned would result in de at the skimmer or suction.

If The manifold is fine, perhaps the mesh on one of your grids is damaged? When the pump is off and fluid level falls in the filter canister, it maybe draws a little de thru??


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[OldPoolMan]

There has to be a hole somewhere in a grid, the manifold, or less probably, the multiport valve. A wild guess: does your filter have a air tube with a screen fitting on top? Sometimes that small screen or the entire piece is missing, which allows de to return through to the pool.

 

[mjones13]

Thanks for all the suggestions and input. I ordered a new manifold which comes with the air tube. Although I can not see any cracks, maybe when it's under pressure when it first starts up a crack is allowing earth to pass through? Then when the pressure equalizes it stops... Part should be here tomorrow, keeping my fingers crossed. Thanks again everyone.