Gerald,
OK. I think I found out what your valve may be. You seem to have a rather sophisticated fresh water tank fill mechanism. When you are connected to outside freshwater and you set your water fill selector to
on it maintains your fresh water tank at a predetermined level using internal sensors. You can leave it in the "on" position the whole time you are connected to an outside source and it will keep the tank level at the predetermined setting. (You can
read about it here, and may even want to download this manual which is located in the Beaver Owner's Technical Information entry on this forum. Specifically refer to page 112.)
Seeing your picture makes it clear that we do not have the same water setup. Our pump "closets" are very similar, but I have no spacing in mine that would even allow for a valve like that. My ice maker filter holder is right where the line for your valve is located. Your holder clearly looks like it has been in the same place since the beginning.
Hope this helps.
Bob