A pressure of 1 Atmosphere = 30" mercury = 760mm mercury = 15lbs/sq" = 760
Torr = 32ft of water = 1 bar = 1000mbar = 1013 hectopascals. (all approx.)

Assuming that the question relates to vacuum chucks.

A metric/imperial conversion shows that for every 67mbar below 1000mbar you
will have 1lb/sq" holding the bowl in place.

If you get down to 67mbar (1000-14x67mbar) you will have 14lb/sq" holding
the bowl in place. Reducing the pressure below 67mbar is an attempt to gain
the extra 1lb/sq" to hold the bowl in place. I would suggest that if the
anyone struggling for the last 1lb/sq" is living life on the edge.

I'm sure Bill Noble's advice would be to make sure the pump has the
throughput to the maintain the target vacuum whilst handling leaks of the
seals and porosity of the wood
and release of water from the wood at reduced pressure.

I hope this helps.

BillR


"Peter Wells" wrote in message
...
On Wed, 20 Dec 2006 01:00:17 -0500, Bill in Detroit
wrote:

How can I correlate mbars, as in :

Ultimate vacuum mbar 1.10-4

with inches of mercury so as to make a comparison between various makes
of vacuum pumps. I'm not in the market today but I'm reasonably
confident that I eventually will be ... so I'm trying to understand the
lingo.

Just asking wikipedia about millibars (mbars) brought me to a nice chart
comparing them to hectoPascals. On this side of the pond, that's still
apples & oranges.

Not sure I understand you: a hectopascal IS a millibar. Shipping
forecasts and reports here (in France) now use the hectopascal as
standard for all atmospheric pressures.
For medical purposes (the only area where it is still used in Europe,
apparently), 1 mm mercury = 133.322 pascal, or 1.33322 hectopascal.

As 1"=25.4 mm, my calculation makes that 1" mercury = 33.864
hectopascal.

Unless I've screwed up somewhere...


only one p in my real address / un seul p dans ma véritable adresse