I have been thinking about this post and would like to contribute
an

idea.  What may be happening here could have nothing to do with
hardware and
everything to do with rheology.  Many common fluids are Newtonian;
that is
to say their viscosity is constant with regard to shear rate.
However,
others, such as polymers, are non-Newtonian and exhibit a reduction
in
viscosity with regard to shear.  Single grade oils and multi-grade
synthetic
oils are pure substances and therefore Newtonian.  But multi-grade
mineral
based oils achieve a viscosity range by adding a polymer to the oil
base.
This may transform the oil to a non-Newtonian fluid and could
exhibit shear
thinning.  When the wall shear stress builds sufficiently, this has a
tendency to cause a flow disruption.  In extrusion of polymers it is
called
melt fracture and is accompanied by wild fluctuations in pressure
and flow;
essentially a chaotic system.  This phenomena is often accompanied
by rather
distinct changes in the sounds produced by the process.  This sounds
a lot
like the description of the oil pump issue.  If true, it would
require
standard mineral based multi-grade to make this happen and not with
single
grade or synthetic grades.

Just an idea.

Charlie Smith
KIS Cruiser 4021

William wrote:

Charlie, Good observation -- I hadn't considered Non-newtonian fluid
behavior before.
Bill Schertz
KIS Cruiser # 4045

It seemed a bit familiar to me.  At least the theory fits the
observations to date.  The other thing that occured to me is that you
may be boiling out some low end hydrocarbon when the vacuum level
reaches the proper point.  Heavens knows there would be enough carbon
or other small particles in there to act as places to initiate the
vaporization.  But if its non-Newtonian, the flow will exhibit normal
forces and that will really muck things up on the output side of the
pump.  As for me being characterized as a rheology expert, only my
pride prevents me from labeling that as a lavish exaggeration
(secretly, I enjoyed it immensely).  I know just enough to be
dangerous.  But sometimes, you need know only just enough.

Charlie Smith
KIS Cruiser 4021

Glad to see another Cruiser on here.

Paul Lamar

Charlie,  thanks for that analysis.  As a person who had never heard
the word rheology before, your comments opened for me a window on
another view of the "real" world.    Very interesting.       Jerry

 
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