What am I missing?
A LBS sold me a spiffy Crankbrothers pump, two-headed, with a gauge and a dial for high volume vs. high pressure, small enough to carry in a bag. All my tubes have Schraeder valves; it's a vintage thing.
Trouble is, I've tested it at home but I haven't yet managed to get any real air into a tire yet.
I can put it on the valve stem and spin the head to lock the seal, but a lot of air can escape during that process.
Once I tried the high pressure setting and after 65 strokes it had gone from maybe 60 to 70 lbs. That's a lot of work for not much result.
The head fits very tightly on the valve stem with the head rotated to make a seal, but with the head released air comes out of the tire.
That means a lot of air escapes from a partially filled tire when you put the pump on to add more air.
The guy at the LBS had said don't release the head to take it off the valve, just pop it off the valve stem. I tried that once and sure enough it popped right off and took the valve right off the tube.
All the air escaped
but fortunately I was at home and had another tube. I can adjust the seal tightness by loosening the cap holding the rubber seal, but to get it loose enough for it to come off the valve easily it doesn't seal completely, so air leaks out slowly while I'm pumping.
There seems to be no middle ground with that adjustment mechanism (which perhaps wasn't meant to be used that way at all).
My 30-year-old Zephal hp still pumps up 105psi with no trouble. Heaven forbid I get a flat on the road while carrying this pump (which I am tempted to spell with fewer letters).
Am I missing something?