Originally Posted by
habilis
....
In the interest of science, I'm tempted to push the pump dial beyond the pressure in the tire to see if that would open the valve. Theoretically, if the pump pressure exceeds the tire pressure, the valve should open. I won't try it, though, because something could break in the pump.
Of course that's how it works. With every stroke, the valve remains closed until the hose pressure exceeds the tire pressure, pushing the valve inward and opening it. After ward then the hose pressure drops the valve closes until the next stroke.
The issue is that valve sticks initially so air alone won't open it unless the differential is super high (mine force open at about 200psi on a 90psi tire). The experiment won't hurt the pump, but repeatedly taking the gauge to the end of the scale can alter it's calibration. SOP in the pressure gauge world is not to routinely run gauges above 80% of the scale range, with staying below 66% being best.