page_title: Snifting valve
section_title: UK railways
hierarchical_section_title: Snifting valve / UK railways
caption_attribution_description: Typical British Freight Locomotives "Mogul" (2-6-0) Mixed Traffic Locomotive, LMS
context_page_description: A snifting valve is an automatic anti-vacuum valve used in a steam locomotive when coasting. The word Snift imitates the sound made by the valve.
context_section_description: UK railway companies did not agree on the merits of snifting valves.  The London and North Eastern Railway used them very widely. The Southern Railway used them for a while but later removed them.  
  The probable explanation for this diversity is that snifting valves were useful as long as steam temperatures were relatively low.  As locomotive development proceeded, larger superheaters were fitted and steam temperatures increased.  When the locomotive was coasting, the air passing from the superheater to the cylinders became so hot that it oxidised the cylinder oil and interfered with lubrication.  At this point, most railways decided to abandon snifting valves.
caption: LMS Crab, showing cylinder-mounted snifting valves
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