K-n-c,Turin, et al, I know it may have been a little tongue-in-cheek,about checking the tyre pressure as well; however what you do on your car is one thing,aircraft are widely different,and wheels and tyres suffer more than your average jalopy .The cap is there as a cover to prevent contamination of the sealing mechanism,from heat, dust, liquids,etc and to act as a second seal if the valve itself fails.If it isn`t there,it should be replaced,not by one you have lying in a tool box/pocket/ashtray,but by a new/clean one.Not only that but any `sensible` engineer should inspect the valve to see if it has failed,or is loose/damaged,and check the tyre pressure as a matter of course,as the tyre may have a failing valve.Consider also the fact that the valve cap has a certain mass/weight,not a lot, but on take-off and landing it can be accelerated to a speed of up to 300 ft/sec on large aircraft.It`s energy probaly won`t punch a hole in the airframe,but it may cut wiring or a hose,or jam in a brake caliper.And ,yes,I`ve done my walkrounds at oo.oo o`clock,from -30 to +40 wet or not,but prefer `normal` working hours now !!
