Air valves are becoming hard to turn

My air valves are getting hard to turn, from the open position to the spring-loaded close position. It still works well when I get it going, however. What do I use to lubricate it?

I recommend using UV Tech on the O-ring on the valve cap. I also spray a little in the bore of the valve to lube the oronge button shaft. This stuff is water based and good for the rubber.