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Attached is an image of an older style
radiator cap, and the neck of its radiator. Note that there are
two seals in the cap (actually 3, but ignore the 3rd for now). In
this system, the lower seal (deflected by my finger) is spring
loaded at the system design pressure. If that pressure is
exceeded, fluid vents out the small tube to an unpressurized
'catch can' that has a vented cap. In this system, air/water
separation happens in the top tank of the radiator. If system
pressure goes below ambient air pressure (after shutdown), the 3rd
seal in the cap (little metal disc in the bottom of the cap) gets
sucked down, allowing fluid to be sucked back into the radiator
from the catch can.
Newer systems, including the Renesis, use a pressurized 'catch
can' (swirl pot) with the pressure cap on the pot instead of the
radiator. The high point of the radiator has a direct path to the
top of the pot, without a pressure cap in the path. The swirl pot
should be 1/3 to 1/2 full, to leave an expansion area when the
coolant expands with heat.
To use the radiator & cap shown with a swirl pot system, I'll
have to remove the bottom rubber seal that my finger is deflecting
in the picture, or remove the little metal disc on the bottom of
the cap. The only seal in the radiator cap will then be the top
gasket, that seals the cap's top flange to the top of the filler
neck.
Some guys add a 'catch can' after the swirl pot (basically move
the radiator cap/vent/catch can system I described above to the
top of the swirl pot), so they can tell if the system has burped
any coolant out of the swirl pot. (That might mean that there's
still air in the engine or radiator, or that the system boiled
over for some reason.)
I'm not sure how critical it is, but the system with the
pressurized swirl pot will obviously work best if the top of the
swirl pot is higher than the vent lines coming from the flywheel
iron, the radiator, and the top of the water pump outlet. It
doesn't seem critical how low the bottom of the swirl pot is. I'm
pretty sure I've seen automotive systems with the bottom of the
swirl pot mounted lower than the water pump inlet.
Hope that helps,
Charlie
On 5/24/2014 12:37 AM, steve Izett wrote:
Thanks Charlie.
That makes sense to me.
Didn’t understand the part of your sentence: “…..and the
radiator 'overflow vent' is open to the top tank of the
radiator, instead of being above a pressure cap seal.”
Appreciate the comments.
Steve
On 24 May 2014, at 9:53 am, Charlie England < flyrotary@lancaironline.net>
wrote:
In this case,
and in Len's drawing, the swirl tank/reservoir is at
cooling system pressure (pressure cap is on the swirl
tank) and the radiator 'overflow vent' is open to the top
tank of the radiator, instead of being above a pressure
cap seal.
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