Newcomen Atmospheric Engine

The Newcomen was first used to pump water from mines in England.  The pump rod at left is coupled to the driving piston by a large rocking beam.

Water is boiled continuously to produce steam.  During the piston's upward stroke this low pressure steam (about 5 p.s.i.) is admitted to the cylinder.  The pressure is insufficient to lift the piston on its own -- the weight of the pump rod does most of the work.

At the top of the stroke the steam valve is closed and a water jet is briefly turned on, cooling the steam in the cylinder.

During the upward stroke, an auxiliary pump fills the cooling water reservoir.

Newcomen engines were successful in part because they were very safe to operate.  Since the steam was under such low pressure, there was no risk of a dangerous boiler explosion.

As near as I can tell, the earliest Newcomen engines featured manually operated valves, as illustrated here.  An operator apparently stood on a platform near the cylinder base and threw the valve levers on each stroke.  (From the illustrations I have available, this engine seems to have stood at least 20 feet tall).  Later Newcomen engines featured automatic valves which were coupled to a pushrod attached to the main beam.

Copyright 2000, Matt Keveney. All rights reserved.