Back Flow Preventer

I just installed a Back Flow Preventer, into a sewer hole, in my basement, its 4 inches in Diameter and fits snug, my only problem is, is I plan on laying carpet down and after installing this tight fit item, The spring that allows the plunger to close incase of a back up sits higher then the the floor with no room to push it down, is this normal? and would it sill work if I laid carpet right over it? because of the way its sitting, it could easily be stepped on...
Any Help would be appreciated.. Thank You

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