Message text written by Hugh Fader
>I recently put my early TR6 oil pressure gage on a NIST-traceable pressure
calibrator. I checked the actual pressure required to get the gage to read
2
kg/cm2, 50 PSI, and 5 kg/cm2. The calibration is way off! Here is what I
found:
Gage Reading Calibrator
PSI (kg/m2) PSI
28 (2) 33
50 (3.5) 62
71 (5) 90
I remember someone on the list saying that the readings went higher as the
gage aged -- possibly because the tube inside became fatigued and easier to
move. Doesn't look like that's the case with mine. Maybe the tube actually
becomes work hardened and harder to move or maybe things get gummed up and
there's higher friction.
<
Hugh brings up a good point. That is: the gauge on your dash is for
indication only. It takes time and effort and test equipment to calibrate
gauges and the factory, looking to contain costs where ever it can,
probably determined that accuracy was less important that we do.
I don't know much about metalurgy but the Bourdon tube that makes the gauge
work may be made of an alloy that will "work harden" which means it will
get stiffer over time rather than more compliant. This will cause the
gauge to read low. The other possibility is that it always read low.
Cheers
Dave
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