Re: 464

Actually, there is one additional telltale mechanism on the outside of some superheated engines. This is a damper control which is a lever with a weight which connects to a small cylinder that fills with steam whenever there is steam coming to the cylinders. Steam in this small cylinder works against the weighted lever to open a damper in the smokebox. This can usually be seen on the side of the smokebox. Inside the smokebox there is a damper plate connected to this mechanism via a shaft. When the engine is at rest the damper prevents draft that might be created by the blower from pulling hot firebox gasses through the super heater flues. This is intended to help prevent burning of the super heater units when there is no steam flowing through them. If an engine has a front end throttle so that appliances such as dynamo and air pumps can operated off of superheated steam, I believe this mechanism would be omitted as the superheater units will always have this steam for appliances flowing through to keep them from overheating. Also in the cab, a superheated engine may have a drifting throttle to allow a little saturated steam to flow to the cylinders to help with lubrication when going down grades with the throttle closed.