I use Vaseline to protect alloy valve caps.
The reaction between brass valves and alloy caps is caused by electrolysis and can be reduced significantly by smearing the brass stem or cap with Vaseline. I had a major problem with brass fire hydrants, alloy caps and salt water (the alloy caps turned into mush). The problem was significantly reduced using Vaseline. The small proportion of failures was attributed to incomplete Vaseline coverage of the alloy cap. Hope this info helps.
Very true. I have also found that, against the advice of aeronautical engineers, Copperease grease between alloy wheels and iron hubs prevents them fusing together, possibly because the copper in the grease acts as a sacrificial anode.
Answered by Honest John on