I'm convinced that the Pentair 261186 Multi-valve is a defective product.
We used this valve as a replacement on an AquaTools AT3115 sand filter after the spider gasket in the original valve gave way. After two months, all the dirt (not filter sand) when vacuuming was coming right back in through the jets. I replaced the spider gasket twice with no luck, and Amazon thoughtfully sent another valve, which failed at 8 weeks of use.
Amazon.com : Pentair 261186 Valve Replacement Sta-Rite Cristal-Flo High-Rate Pool and Spa Sand Filter : Outdoor Spas : Patio, Lawn Garden
Here's a pic. I used floculant and opened up the return in the smaller separate part of the pool, so that the two jets in the main part of the pool had minimal pressure. Essentially, all the "filtered" water goes here first:
Microsoft OneDrive - Access files anywhere. Create docs with free Office Online.
It's a 4500 gallon in-ground concrete/tile pool with a 1hp pump. If anyone has any ideas I'd love to hear them. I've backwashed, deep-cleaned, ect. to no avail.