Just a guess.........
Filter bypass so you can change filter with water supply still ON (or filter is clogged)
Side to side position....water flows thru filter
Turn it 1/4 turn (top to bottom) and no water to filter
Is it time for YOUR Medication or Mine?
Dodge 3500 w/Tractor Motor & NUWA 5vr
US NAVY---USS Decatur DDG-31