Editing Newcomen atmospheric engine (section)

===Operation===
The pump equipment was heavier than the steam piston, so that the position of the beam at rest was pump-side down/engine-side up, which was called "out of the house".

To start the engine, the regulator [[valve]] '''V''' was opened and steam admitted into the cylinder from the boiler, filling the space beneath the piston. The regulator valve was then closed and the water injection valve '''V'''' briefly snapped open and shut, sending a spray of cold water into the cylinder. This [[Condenser (heat transfer)|condensed]] the steam and created a partial vacuum under the piston. Pressure differential between the atmosphere above the piston and the partial vacuum below then drove the piston down making the [[Stroke (engine)|power stroke]], bringing the beam "into the house" and raising the pump gear.

Steam was then readmitted to the cylinder, destroying the vacuum and driving the condensate down the sinking or "eduction" pipe. As the low pressure steam from the boiler flowed into the cylinder, the weight of the pump and gear returned the beam to its initial position whilst at the same time driving the water up from the mine.

This cycle was repeated around 12 times per minute.

====Snifting valve====
Newcomen found that his first engine would stop working after a while, and eventually discovered that this was due to small amounts of air being admitted to the cylinder with the steam. Water usually contains some dissolved air, and boiling the water released this with the steam. This air could not be condensed by the water spray and gradually accumulated until the engine became "wind logged". To prevent this, a release valve called a "snifting clack" or snifter valve was included near the bottom of the cylinder. This opened briefly when steam was first introduced, and non-condensable gas was driven from the cylinder. Its name was derived from the noise it made when it operated to release the air and steam "like a Man snifting with a Cold".<ref>"A Course of Experimental Philosophy", John Theophilus Desaguliers, 1744, Vol II p. 474.</ref>