It is typically not necessary for the valve in a Shrader valve to press open the valve on an air chuck. Indeed, in almost all cases -- every case I have ever tried, you can get the air chuck to operate even when the valve has been removed from the Shrader stem. Watch someone install auto or truck tires and you will believe me. What presses against the valve in the air chuck and opens it is the barrel of the Shrader valve stem. The Shrader valve stem is a standard inside and outside diameter and air chucks are made so that the barrel will open the valve on the air chuck. The problem with some air chucks and with some Shrader adapters (and some valve stem extenders for truck wheels and the like) is that if the inside diameter of the adapter is slightly larger than a standard Shrader stem, it will not open the valve in some air chucks. In my experience, the angled dual head Milton brand air chucks are the most likely to work. Here's a pick of the one I mean: