"Orval Fairbairn" wrote in message
news
In article , Ray Toews wrote:

I am removing the vac T&B and putting in an electric and thinking of
removing the regulator and then apply full venturi vacumn to the
horizon. Is it possible to over rev a gyro with an outside venturi?
I am doing this because even after a 15 min runup I am several miles
off the runway before the horizon stabilizes, not that great on a nite
takeoff.

Ray

Vacuum gyros are meant to operate at a specified vacuum level, in order
to maintain their proper RPM. Applying extra vacuum would cause them to
spin too fast and cause premature wear on the bearings.

This is one of many reasons for vacuum pumps, instead of venturis.

Uh..don't think so. There is a vacuum regulator in the system.

I had an emergency vacuum system on my Archer made by Precise Flight that
used full engine manifold vacuum in place of the vacuum pump should it fail
and the regulator still delivered a steady vacuum at 4" H2O. I don't think
a venturi would ever produce as much vacuum as an engine at idle.

Now that I think of it, the pitot/static pressure differential at 80 knots
is 4" of water column - the same as the vacuum instruments need. Over 80
knots, you don't need a venturi, just ram air and a static port outlet - and
filters, of course.

Bill Daniels