Paul;
I have the same setup on my airplane; 23-24# cap on filler neck, 13#  cap on
the overflow bottle.  I also have a Schrader valve to pressurize the system.
I have done this, and the pressure goes up to close to 40 psig. before
pressure relieves from the overflow bottle.
The 24# cap is a Moroso and does not leak when the overflow bottle is
pressurized.  The 13# cap is a cheapy (probably from Autozone :) ).  It
could be that a cheapy primary cap would leak at upper seal with the
pressure on the relief side.

If one were to fill the system and the overflow bottle; coolant would vent
overboard on the initial heatup.  Air would be drawn back in on cooldown,
and be compressed on subsequent heatup.

When running the engine I find that the pressure gets up to 23# relatively
quickly, and then slowly continues up as the air in the overflow bottle is
compressed.  The pressure drops quickly with some cooldown to the pressure
in the overflow bottle (as expected, just a bit of contraction in the system
drops the pressure across the primary cap to zero).

That's the point of having the two caps.  Otherwise a decrease in engine
power (and concomitant slight drop in coolant (and engine temp) results in
zero system gauge pressure.
This is necessarily a problem, but if you level of at cruise with high
engine rpm; you might like some pressure in there.

Al

----------------------------------------------------------

All this maybe true Al but why do it that way? Assuming for the moment it
works I see no advantage over the RX8 one pressure can way of doing it.
I see at least one disadvantage and that is there are more areas for
potential leaks to develop. Two caps to fail instead of one.
""
    That's a valid question.  It is partially answered above. The idea
was rapid buildup of pressure, and some pressure on the system under all
operating conditions.  If I were doing it over I may go with a single tank
with something like a quart of air volume over the coolant at ambient
conditions.  It seemed like the right idea at the time, and appears to work
fine.
""
You need at least two pressure gages. One on the main system and one
on the hose between pressure caps to monitor the function of
the series system.
""
    I see no need for measuring pressure on the secondary cap.  If it
went to zero it's no big deal.  I've considered for low altitude short
flights I may leave the second cap unsealed (at the first notch) just to
reduce the pressure on the system.

    Air bleed-off has proven to no problem in my system.  There is
manual air bleed at the highest point from the engine (exit from WP) and
lines from the high point in each rad tank, where air would get trapped,
going back to the filler neck.  It works fine following fill-up, and  after
a couple of temp cycles there is no further air in the system.

Al


The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2005 All world wide rights reserved.