The Mouat Vapor Heating Return Vent (Birdcage Vent)
The Mouat Vapor Heating Co. used to install a vent on the return piping that was quite unique in its appearance and its operation. If you have one of these gems in your basement, make sure it stays there. These vents have NO moving parts. Isn’t that beautiful? A mechanical device that works without any moving parts! So if someone wants to remove it from your basement it may be more likely that the person just wants the device to shine up and put on the corner of their desk, than it is that it no longer works. It is okay to add modern vents along side the original for added capacity, but why remove such a beautiful work of engineering.
These devices were installed only on the dry return piping. They were never installed on the steam supply side of the system.
You can read all about how the device does its job with no moving parts by reading Mouat’s Patent on his air vent .