Thread: calibrating cheap air gauges

I bought a gauge from Motorcycle Accessories recently and it was well and truly inaccurate. Just what I wanted for my bike tyres - not! At least I got a refund. I wonder if one can buy an accurate gauge any more.

The gauge on my tyre inflator came out of a mid-Sixties US magnetic storage device (the equivalent of a modern disc drive) where the heads were operated by compressed air.

Originally Posted by PhilipA

There is no adjustment on the air horn thingo ,

The Bourdon tube?

PhilipA The standard way to calibrate a gauge for a linear error is to simply move the pointer as you have done. It gets interesting when you have a non-linear error, on P38rovers's diagram you see a lever coming off the bourdon tube, that lever connects to a sector gear arrangement that drives the pointer(except really cheap crappy gauges that have no sector gears were the lever directly actions the pointer). The higher quality gauges have multiple attachment points on the lever and sector gears to allow the gauge to operate in the most linear portion of the bourdon tube.

The bourdon tube does have gears in the SCA gauge , but no apparent means of adjustment. There is a U shaped connection between the bourdon tube and the first gear and this may be the legitimate adjustment , but I was not game to touch it, as once bent it would have been difficult to undo .
Regards Philip A