"Floating a Valve"

Terminal Velocity... A object can only stay in motion for so long increasing speed so fast before the molecular or composite materials Freeze Motion.

English means The spring is rated to push the valve closed only so fast, once the cam overtakes the speed of the Springs capacity to be sprung the valve stays in one direction.. down, once down the piston Hits the valve breaking the valve or worse shoves it through the piston when spraying.

Why things break when you spray. N20 is Sub Freezing when expanded. A engine internally runs around 200 degrees +. When N20 is sprayed into a heated combustion chamber the expanded gas's freeze the metals persay, but intern SOFTEN the metals. To much spray and you "burn" holes in your pistons melting them. A valve Being bent is what occurs the breakage happens when something mechanically hits the valve and breaks it. LIke i think KJ said The cycle of HOT COLD cycles breaks down the molecular strength of the metals in the engine weakening the components. Exhaust Valves like stated go first die to the heat since they dont see any cold N20/Air mix, it just gets Super Heated Exhaust. Intake Valves 99% of the time bend when sprayed and are broken uppon impact of the Cam lob or The piston. Cylinder Wallsalso give way like this Softened Metal and "Burns" holes in the cylinder wall.

I hope i Helped and didnt confuse ya !