page_title: Smokebox
section_title: Spark arrester
hierarchical_section_title: Smokebox / Spark arrester
caption_attribution_description: Rail transport modelling in Schifferstadt, Germany
context_page_description: A smokebox is one of the major basic parts of a steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler. The smoke then enters the smokebox, and is exhausted to the atmosphere through the chimney. Early locomotives had no smokebox and relied on a long chimney to provide natural draught for the fire but smokeboxes were soon included in the design for two main reasons. Firstly and most importantly, the blast of exhaust steam from the cylinders, when directed upwards through an airtight smokebox with an appropriate design of exhaust nozzle, effectively draws hot gases through the boiler tubes and flues and, consequently, fresh combustion air into the firebox. Secondly, the smokebox provides a convenient collection point for ash and cinders drawn through the boiler tubes, which can be easily cleaned out at the end of a working day. Without a smokebox, all char must pass up the chimney or will collect in the tubes and flues themselves, gradually blocking them.
  The smokebox appears to be a forward extension of the boiler although it contains no water and is a separate component.
context_section_description: A spark arrester is often installed within the smokebox.  This may take the form of a cylindrical mesh running from the top of the blast pipe to the bottom of the chimney. The purpose of a spark arrester is to prevent excessively large fragments of hot ash from being exhausted into the environment where they may pose a fire risk. For this reason, spark arresters are generally installed on locomotives running through dry environments. They should not be confused with the external spark arrestors fitted to some locomotives. The presence of a spark arrester may have a thermodynamic effect, distorting the draw of air over the fire and thereby reducing total power output. Thus their use can be contentious.
caption: Model steam locomotive showing spark arrester mesh
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