I have no problem understanding how a mechanical pressure gauge works, but how does a mechanical temperature gauge work? Seems like you'd never get the accurate temperature to the gauge through a little tube that's not insulated.

capillary  tube.       Kinda like a   miniature   hydraulic line...  and  your   dial  is  actually  a  pressure gauge   

The  probe  has  a  small reservoir  of    (older  units  had  a  low  flash point type  fluid similar to  ether)   and  when it  warms up,  the fluid  expands,  and  then  moves  the dial.

 

 

you can't  cut the line to shorten,  or   even  bending it  too   sharp.    Ok,  according to the post below,   there are apparently more than  one way to  measure  'heat'   mechanically.      I've been   around  enough  older crap to  know that the  capillary tube  has  pretty nasty  smelling  stuff in it  when it's  broke.      Especially  when   trying to remove the  sensor from a  'well rusted'   port!

 

 

Mechanical pressure gauges are connected directly to the process fluid being measured (i.e. oil). As the process fluid pressure changes the pressure on the bourdon tube also changes which in turn moves the pointer on the gauge.

Mechanical temperature gauges also utilize a bourdon tube. They have a sealed capillary tube and bulb assembly that is filled with temperature sensitive liquid that produces a proportional vapor pressure on the bourdon tube. As the temperature changes, the pressure inside the bourdon tube changes, which in turn moves the pointer on the gauge.

Edited March 2, 201411 yr by rancherman

The thermocouple reacts to the differences in temperature by sending electrical signals to the gauge.  The gauge then deciphers those signals and turns it into something you can understand.  If you're totally stumpted then simply google how a thermocouple works and I'm sure there's ample website which can explain it in simple form.

capillary tube. Kinda like a miniature hydraulic line... and your dial is actually a pressure gauge

The probe has a small reservoir of (older units had a low flash point type fluid similar to ether) and when it warms up, the fluid expands, and then moves the dial.

you can't cut the line to shorten, or even bending it too sharp.

Ok, that makes sense. Thank you!