Snifting valve
On railways which did not use snifting valves, drivers were instructed to keep the regulator slightly open when coasting to avoid creating a vacuum.
Alternatively, the valve rests on its seat under gravity and is lifted by inward air flow, which can give rise to a characteristic rattle when a locomotive is coasting.
The drawback of this arrangement is that they admit cold air which cools the cylinders and leads to condensation when the steam is turned on again.
[citation needed] The probable explanation for this diversity is that snifting valves were useful as long as steam temperatures were relatively low.
[citation needed] With somewhat different functions, snifting valves were also used in atmospheric steam engines, hydraulic rams and with residential well-pumps.
The snifting valve is the small mushroom directly behind the chimney.
The square cover beneath is another distinctive LNER feature, covering the end of the superheater header.
