Newcomen Atmospheric Engine Description

The engine photos on this page were taken of engines exhibited at the Henry Ford Museum in Dearborn, MI.

Figure 1. Newcomen pump (1760):
20 hp
14 strokes per minute (estimated)
Bore 28"
Stroke 72"

This Newcomen engine is from approx. 1760. It is the oldest Newcomen engine in existence. The person in the photo gives you some idea of the scale! Note the large wooden beam and support structure. The original Newcomen engine (1712) was more primitive than then engine shown here.


Figure 2. Newcomen pump (1760). This view shows the steam piston.

Figure 2 shows the steam piston, the boiler, steam line, and feed water line. The feed water line passes through a tank before dropping to the boiler. This permits any air bubbles entrained in the feed water line to exit before the water enters into the boiler.

This engine incorporates some improvements relative to the earliest Newcomen engines. In Newcomen's original implementation, the boiler was placed directly under the steam piston, and the steam piston needed to be mounted relatively high. Building a rigid structure high off the ground that could take the tremendous pounding of the steam cylinder was difficult. Later pumps used the separate boiler shown here and the piston could be placed closer to the ground. Published descriptions of Newcomen pumps include illustrations showing the pump protected by a roof built from the center of the main beam over the steam cylinder and boiler. This auxiliary roof construction was also simplified by placing the steam piston near the ground.

Description of Operation

The actual design of the water pumps is difficult to discern from the exterior of the museum exhibit, and they are illustrated as if they expelled water on the downward stroke. It is possible that they expelled water on the upward stroke. The designs for the alternate arrangements are described on the pump page, as well as a description of the check valves D-J which operated automatically to prevent backflow.

Step 1 - upward stroke of steam piston.

Valve A is open, and valve B, C are closed. Weight of the pump side pulls beam down on the right expelling water from the main pump. (On some engines extra weight is added to the pump side of the beam to assure it is heavier than the steam side). This action pulls up the steam piston, and pulls steam into the cylinder. Note that the steam piston is attached by a chain - it can't push up the beam! The boiler operates at nearly atmospheric pressure. During this upward motion, steam piston condensate from the downward stoke is pulled into the condensate pump.

Step 2 - downward stroke of piston

Valve A is closed, valves B and C are opened. Water is sprayed into the cylinder below the piston to condense the steam, creating a vacuum inside. The atmospheric pressure on the outside pushes the piston downwards. This action pulls down the beam and fills the main water pump and auxiliary pumps. The top of the cylinder is open and the piston is visible from the top. Water is sprayed onto the top of the piston via valve C to maintain a good seal. Even though Newcomen was a blacksmith, he couldn't make perfectly round cylinders in those days. The cylinders were typically cast and slightly out of round, as well as the pistons! The seal was made by a packing of oakum (hemp fibers soaked in tar) that was jammed in a channel between the piston and cylinder and held in place by weights. Newcomen found it necessary to keep the seal wet in order to maintain the vacuum.

Early Newcomen engines simply drained the condensate water from the steam piston. In the engine illustrated here, a condensate pump is provided that sits in a well that would have been filled with water, presumably pumped from the mine by the main pump. This particular Newcomen engine also has an auxiliary pump to provide condensing water. The internal portion of the water reservoir at the top of the beam support isn't visible from the ground level at the museum, but it probably has separate reservoirs for the hot condensate that returns to the boiler and for the cold condensing water.


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