Jeff Travis writes:
>>>> 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.
>>> Jobst, could you provide more detail on this? I'm intrigued.
>>> 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.
>> 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.
> 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.
>>> 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.
>> 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?
> 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.
> 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.
>> I get the impression we aren't talking about the same pump head and valve stems.
> We are. I can't think of a better way to describe it.
> 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 protected]
