Maybe you have your own bicycling frustrations. Breaking off valve stems has been mine.
The first time occurred after I patched a flat during Cycle Across Maryland, pumped up the tire, and the innertube started leaking at its connection with the valve stem. It happened twice on that trip.
I chalked it up to “bad innertubes,” but this has continued to plague me year after year, regardless of brand. Ever since I became a firm believer in Mr. Tuffies and graduated up to Armadillo-style tires, this has been just about the only kind flat-out that I encounter.
The latest occurrence resulted in a slightly bent mounted tire pump; I had thrown it down in disgust. When I picked up a fresh innertube Wednesday, I asked the guy at the bike shop what was going on.
Does it happen with the floor pump?
No, just when I use the pump I carry.
What's probably happening, he surmised, is the o-ring that seals the pump onto the valve stem is slightly worn on the often-used floor pump so it slides on and off easily. Not so with the bike-mounted pump, it gets stuck on the stem, and the valve stem separates from the innertube as you pull and yank it.
How to remedy? Don't push the tire pump so far onto the stem, just enough to make a seal. To remove, gently twist it back and forth until it comes off.
Jees. Why didn't I think of that?
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