I have installed 1 micron filter bags on the pool returns and am collecting a lot of large material that should never get though the sand filter. The by-passed material is light weight and will float on water. It is mostly debris from trees like leaf husks, small bits of leaves, small pieces of grass, and even some ant bodies.
I'm positive the material would not get though the filter so it must be by-passing the sand. As far as I know there are only two ways that can happen; first would be the area around the upflow pipe where it slips into the multiport valve. The other would be if the spider gasket on the valve was leaking by. There are no leaks from the back wash pipe when the valve is in the filter position and no flow back to the pool when in the back wash position. So my first guess is there is a large enough gap between the up flow pipe and the valve inlet to allow debris to by-pass the sand.
As far as I know there is no seal ring or O-ring between the upflow pipe and the inlet to the multiport valve. There is only a slip on slotted pipe connection. Since the pressure is greater at the top of the filter where water enters a loose connection would allow a by-pass.
Has anyone experienced this and what can be done to stop or at least reduce the by-pass?