Re: Question about a Locomotive Feature

Opening a vent on the front of the smokebox, would force air into the smokebox while the engine moves forward, as has been suggested. But this added draft will not add draft to the fire because it would have to travel counter to the normal firebox draft which enters the firebox grate and passes forward through the fire tubes.

Actually, this device is intended to reduce or shut off the normal functional draft that is pulled into the firebox and on through the fire tubes. It does that by offering an alternate draft inlet that bypasses the normal draft route into firebox and through the tubes.

While some added air might be forced into the damper opening by forward travel, the majority of incoming air will be pulled in by the vacuum produced by the exhaust nozzle ejecting steam up the stack. Opening the damper allows this vacuum to pull air in through the damper and thus reduces the pull through the fire tubes.

This damper device is not as obscure as I thought it might be. I find three more patents on a variation of it. Some of the patent language describes the purpose as preventing a strong draft from tearing holes in the fire by lifting coal off the grate.