At 09:58 PM 1/20/2001, Bill Davidson wrote:
>Pressure is pressure... right.... BUT the innards of one gauge may be built
>for one fluid and yet seals may dissolve with a fluid they are not designed
>for.... dunno but something to think about.... especially when you're

Mechanical pressure gauges use a Bourdon tube mechanism -- a flattened
coiled tube that starts to uncoil proportionally to applied pressure.

All the ones I've ever looked inside have had soldered brass or bronze
movements (though brass certainly wouldn't work for ammonia).   If you have
a gauge lying about you can open it up and see -- but I doubt there's
anything but metal once you get into the actual gauge.  I'd be more
concerned about hoses leading to it.

david

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"