Previous owner thought it controlled the jets. It doesn't seem to have anything to do with them at all. I think its connected to the two pipes in the third picture. As far as i can tell those pipes don't seem to have a function.
This is my first pool so it might be obvious but my googlefu is failing me.
http://imgur.com/a/o53en this is the album I put together. I couldn't get the pictures to upload on this post.