Jim T., I think silicon goop will certainly render the purge valve itself inoperative, (eiher closed or open!) but silicon will not prevent the plastic purge valve from popping out of the mask. The valve usually is held in place by a thin rim of mask material which fits into a groove on the valve. Mask material, generally a silicon compound, is extremely resistant to any kind of glue or bonding. Silicon cement will not bond to silicon. In fact silicon does not bond well with anything other than glass, which is why they use it to hold aquariums together. I agree that purge valves are a bad idea, especially because they tend to pop out more easily after the first time.