Quote Originally Posted by BigDave View Post
I don't see an air relief line.
You're right -- my inexperience with top-mount filters is showing!

+ I don't see how you can mis-orient the valve, unless you mean with respect to the piping. Is that what you mean? . . . I have no idea what would happen if you hooked the pump discharge to the filter outlet, and hooked the outlet to the pool return!

+ Another possibility is that the filter was overfilled with sand . . .

+ And, yet another: if anything was done to INCREASE flow through the filter (bigger pump, removed pipe-line obstructions, etc), then sand will leave the filter during backwash, but a small amount will remain in the diffurser and return to the pool when normal flow is restored.

In both cases above, using the rinse position should remove that sand before it can enter the pool.