I have been out of the loop for a few days.  This morning I read the
series of posts on the P-can system proposals.  I must weigh-in strongly
against the P-can concept for the rotary (in an aircraft).  It will lead
to premature failure of the O-ring housing seals.  Here is why.

As Paul has said many times, the devil is in the details.  The O-ring
seal is a wonderfully simple type of self-pressurizing seal.  But, it is
not as simple as it seems.  As a self-pressurizing seal it must deform
under pressure to seal properly.  As you can see in the cross section
drawing I've attached, the ring is forced by the fluid pressure against
the three confining surfaces and the deformation of the ring creates the
seal.  O-rings work very well as long the surfaces are clean.  Now
imagine reversing the pressure differential so that the O-ring is forced
to the other side of its groove.  Now the required deformation is in the
reverse direction.  O-rings do not work very well under alternating
pressure differences like this.  The O-ring surface degrades from
abrasion.  And, more importantly for the rotary housing seals, unseating
the O-ring from its sealing surface allows contamination of the sealing
surface by particles in the fluid.  In the case of the housing seals,
when the engine is running the seals are forced outward, away from the
rotor.  The P-can pressure would force them inward during the entire
time the engine was not running.  I think this would quickly lead to
seal failure.  Of course, the normal auto type system places a reverse
pressure on the O-rings upon shut down when the engine is hot.  But,
this pressure is only present for a short time until the engine cools
enough to cause the partial vacuum that allows coolant to flow from the
overflow bottle.

In summary, the design should insure that during quiescent periods, the
pressure differential across the housing O-rings is essentially zero.
This requirement pretty much requires an overflow bottle at atmospheric
pressure.

I suspect that we will find that Dave Leonard's recent loss of coolant
was caused by catastrophic O-ring seal failure brought on by
contamination of the seal surfaces with stop-leak when there was a
pressure reversal on the O-rings.

Respectfully submitted,
Aubrey

What forces the O-ring outward during normal operations? The
combustion chamber goes both ways. Positive pressure on
compression/combustion/exhaust and negative on intake. Does the intake
part of the cycle move the O-ring inward? Is it a combination of
pressure and motion? Which way is the rotor dragging the O-ring during
intake . A drag towards the center could make up for the negative
pressure in the chamber.
--
Blake C. Lewis



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