It looks to me like a sand filter, evidenced by the multiport valve in the second picture. However, unless that model works much differently than mine, the handle appears to be malfunctioning, which could let sand and dirt into the return water. When you push the handle down and move it to another position, does it "click" into place, or does it just stay pushed down when you let go?

It looks like maybe the spring has gone bad, and if so, probably the gasket needs to be replaced as well. What do you hardware experts think?

Janet