The Horizontal High Pressure Engine

Most boats, both side wheelers and stern wheelers were powered with either the Mississippi lever type engine or the slide valve type engine favoured on the west coast.

High Pressure Horizontal Engines
Most sidewheel and sternwheel boats used two high pressure horizontal engines. When steamboats started operating on the Mississippi, around 1807, virtually all marine steam engines were very low pressure and very heavy. These engines were not satisfactory for shallow draft river boats. After much experimenting they developed a light engine with enough power to push a sidewheel boat upriver against the current. They used over 100 psi. When you think that most steam engines used around 5 psi and a bit later 15 psi these engines were extremely high pressure.

The Mississippi Lever Engine. A high pressure engine using poppet valves activated by levers was used in the western rivers, prairies, Yukon and California. The engine consists of a long cylinder mounted on a horizontal bed. The piston rod is connected to a crosshead that moves on guides. A pitman arm connected to the crosshead turns the crank on the paddle shaft. On a sternwheeler there is a separate engine located on each side of the main deck. The cranks on the paddle shaft were set 90° apart to avoid a number of problems.

Steam poppet valves were located on each end of the cylinder. A pipe containing live steam connected the two valves. The other side of the engine had two poppet valves for exhausted steam. They were also connected by a pipe. Each valve had a long lever connected to it. These levers were used to open and close the valves. The valve gear, located in the middle of the cylinder, had wiper levers connected to rocker shaft to raise and lower the levers. The rocker shaft was activated by reach rods that were often connected to a calm on the paddle shaft.
The valve gear was quite complicated and varied from engine to engine. At first going from ahead to astern was heavy work that required a man on each engine. Later this was simplified with the introduction of “ship up jacks” and “lever jacks.”
Horizontal High Pressure Engines on West Coast Boats
These engines have a totally different type of valve system. They used slide or piston valves, similar to the ones used on other types of steam engines instead of the poppet valves. These valves are operated by valve rods running out to the eccentrics on the paddle shaft. Small engines might have one set of valves in the middle of the cylinder but normally the valves were located on each end. However we have seen one larger compound with the valves in the middle of the cylinder. If a cut off was used there rods went to a separate set of eccentrics. There were many versions of these engines. The type of valve gear seems to depend a bit on where the engine was built. They are far easier to manoeuvre than the lever type engine, a great plus in fast water. The engineer has only one lever and a throttle to operate. Other levers were there to operate cut off valves and compound engines.

We found there are many versions of these engines. The valve gear on the western slide valve engines varied a lot. Some of them built in the east carried over some of the characteristics of the western river engines.

More information on marine steam engines can be found in Smoke Ash & Steam

To go back to history page

Lever type engine.The starboard engine on the Bell of Louisville. This working engine is typical western rivers engine.

The valve gear on the engine

.Small engine from the Enterprise. There were many smaller boats plying the west coast. This is a slide valve type.

W. T. Prestons engine. The snag pullers usually had smaller engines.

The Kenos' small engine. This shallow draft boat had a cut-off that would be hard to adjust.

 

Diagram of a typical slide valve engine. Slide, or piston valves were used on most west coast an northern river boats. In most cases the valves were operated from rods going to the eccentrics on the paddle shaft.

Engine on the Sampson V. This is a simple high pressure engine without cut off valves.

Engine on the Moyie. This engine has cut-off valves as in the diagram.

Compound engines. The 3 engines above are all compound engines. The valve gear and cut-offs are all different. Compounds were more common on the larger lake stern wheel boats.

The tug Portlands' engine. She is the last sternwheel tug on the Columbia River. This is a far more modern engine.