Jeff Travis said:Quoted message said:Quoted message said:> I modified my pump head to have a pressure release so that it can be pulled off with no
> pressure. This makes it a tiny bit easier on the rubber.
Quoted message said:Quoted message said:Quoted message said:Jobst, could you provide more detail on this? I'm intrigued.
Quoted message said:Quoted message said:Quoted message said:It seems like the hole in the new grommet must be the same size it has been since the days of
smooth-sided valve stems. Nowadays valve stems are almost all threaded, and slightly fatter to
boot, so the chuck and stem are locked in a death grip when the tire's inflated.
Quoted message said:Quoted message said:Huh? When did we have smooth valve stems? I've been using tubes with Presta valves a long time
now and only the oddest French tubes (that I avoided) had smooth stems.
Quoted message said:Many tubulars used to have smooth stems, for one thing.
I rode tubulars for a long time, none which had glued in stems, and therefore, had threaded shafts,
necessary to clamp a latex, light weight tube onto the stem (or the converse). Only slugs had smooth
stems. As it happens, these stems can be used to fix a butyl tube whose stem separates. I always
carry on in my patch kit.
Quoted message said:Quoted message said:Quoted message said:I've lost track of how many tubes I've ruined trying to push the chuck off the valve stem when
it's under pressure. I ream out the grommet with a tapered hand reamer, and that helps some, but
it sounds like your solution would be preferable.
Quoted message said:Quoted message said:What's this "push the chuck" action. These are easily pulled off with a small tug. That's what
the knurling around the body of the chuck is for. How can you ruin a valve stem that way?
Quoted message said:Not ruin the valve stem, but partially ripping it out from the tube. So the tube is ruined.
As I said, there is something I don't see here. I've been pulling my Silca pump head off stems
for many years now and have never had a failure. None of the riders who use my pump have had
any problems.
Quoted message said:The grip of the chuck on threaded valve stems is too tight to pull it off after the tube has been
brought up to pressure. The only way I can get it off is to push really hard with both thumbs on
the end of the bell. Do this enough times and eventually the valve stem partially tears out of
the tube.
Quoted message said:Quoted message said:I get the impression we aren't talking about the same pump head and valve stems.
Quoted message said:We are. I can't think of a better way to describe it.
Quoted message said:Nonetheless, the motivation for my original post was to see if you would be willing to provide
further details of your pump head modification for pressure release that you mentioned earlier.
Well there is a problem there. Silca used to have a pump head that was a bit larger in body so I
bored a hole in the side and faced the inside to be flat instead of curved. By putting a brass push
button with a half depth O-ring groove in its mushroom stem. I have a release button on the side of
the chuck. The thing is designed to have a minimal stroke of about 1mm. The O-ring groove is almost
at the end of the button stem.
I'm sure I could come up with another way of doing this with the current Silca pump chuck. I have
more than one pump and only my usual one has this feature.
I did this to reduce wear on the grommet but it also eases removal so that the chuck comes off as
easy as it goes on. If you have a gauge on your pump, be sure to free up the valve before putting
the chuck on and pumping because otherwise the gauge will be ruined as pressure goes over 200psi at
the stuck valve. I have a few such gauges lying around from dorks who used the pump.
Jobst Brandt [email hidden]
