Quick question - without me having to do much experimentation, does
anyone out there know if a grease fitting is made well enough to hold
air pressure? I have an application in mind, but a normal schrader
valve won't work, but a grease fitting (if silver soldered in
position) probably would be okay.
Not a grease fitting expert but my little loader / backhoe has 37 fittings
and almost every one of them spits some grease back out after I put grease
in. My bet would be they won't work for holding air.
Look around for "presta" valves. They're like schrader valves, but a
lot skinnier and definitely hold air. As cheap as going to a bike shop
and asking for any dead inner tubes with presta valves in 'em.
If you do go with a grease fitting, I suspect one made of brass (hard
to find, but I've seen 'em before) would have a better chance of
actually sealing air. You could also try adding a drop of air tool oil
to help it.
Why would a presta work better than a schrader? The schrader
valves are available with 1/8" and 1/4" threads, which makes
them very convenient to use, and they hold just as much
pressure as the presta.