Once you add in valves to let air in and out you run into the exact same fouling problems. Snow, small pebbles, road grit, any one of a number of things is at s

Once you add in valves to let air in and out you run into the exact same fouling problems. Snow, small pebbles, road grit, any one of a number of things is at some point going to get sucked into that cavity. Normal stem valves avoid the problem by having a screw-on cap, which'd hardly work for a valve that needs to be passing air all the time.