Sealing cabin heat shuttle

[Flying Canuck]

So, I'm working on all of those firewall penetrations with a constant eye on sealing everything so firewall gases can't enter the cabin. I'm looking at the Van's standard cabin heat shuttle and it's designed such that it seals when you have cabin heat closed. However, when cabin heat is open, there are significant gaps along 3 edges of the valve plate as well as another gap on the other side. Now I understand that the cabin heat airflow will probably be a whole lot more than the leaks around the edges, but isn't this still a pathway for bad air into the cabin?

[lr172]

The air forward of the firewall isn't necessarily bad, only the potential to be bad with leaks. Don't forget that there is a huge amount of clean cooling air flowing through the cowl at any time, making any bad components a small percentage.

I can't imagine that any of the small leak points that you mention can make a meaningfull impact given the large volume of, theoretically, clearn air coming from the heat muff.

Larry

[rvbuilder2002]

The air supplied to the valve from the heat muff has to be at a higher pressure than the air in the lower part of the cowl otherwise when the heat valve was only half opened, lower cowl air would be pushing its way around teh door and into the cockpit. It doesn't.
In the same way, the higher pressure of the heat muff air likely leaks out of the small openings in the corners.

[Flying Canuck]

Thanks, that makes sense. I hadn't even thought of the half open scenario. There's no sealing that opening. And if the air were to get really bad, as in smoke, the emergency procedure would have you close the cabin heat which is sealed.