2-Cyl, 1/2 HP @ 90 RPM
Join Date: Oct 2003
Bikes: 04' Specialized Hardrock Sport, 03' Giant OCR2 (SOLD!), 04' Litespeed Firenze, 04' Giant OCR Touring, 07' Specialized Langster Comp
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On my pump, you lift the tab to lock it to the valve, then lower it back down (like in the first picture) to unlock it. However, the plastic ring around the nozzle is like a screw. When you lift the tab, a cam compresses a piece of rubber so that its diameter gets smaller and grips the valve. But if when you lift it it still doesn't grip, you can adjust the pre-tension on the piece of rubber by turning that ring so that the final locked diameter of the nozzle is a bit smaller.
It could be that the thing was adjusted so that the diameter was the "locked" diameter before you even engaged it.