An oscillating cylinder steam engine (also known as a wobbler in the US) is a simple steam-engine design (proposed by

William Murdoch William Murdoch (sometimes spelled Murdock) (21 August 1754 – 15 November 1839) was a Scottish chemist, inventor, and mechanical engineer. Murdoch was employed by the firm of Boulton & Watt and worked for them in Cornwall, as a steam engin ...

at the end of 18th century) that requires no

valve gear The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle. It can also serve as a reversing ...

. Instead the

cylinder A cylinder () has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infinite ...

rocks, or oscillates, as the crank moves the piston, pivoting in the mounting

trunnion A trunnion () is a cylinder, cylindrical Boss (engineering), protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. In mechanical engineering (see the Trunnion#Trunnion bearin ...

so that ports in the cylinder line up with ports in a fixed port face alternately to direct steam into or out of the cylinder. Oscillating cylinder

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

s are now mainly used in toys and models but, in the past, have been used in full-size working engines, mainly on

ships A ship is a large vessel that travels the world's oceans and other navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally distinguished from boats, ...

and small

stationary engines A stationary engine is an engine whose framework does not move. They are used to drive immobile equipment, such as pumps, electric generator, generators, mill (grinding), mills or factory machinery, or cable car (railway), cable cars. The term u ...

. They have the advantage of simplicity and, therefore, low manufacturing costs. They also tend to be more compact than other types of cylinder of the same capacity, which makes them advantageous for use in ships.

Operation

alt=oscillating cylinder diagram, Operation of a simple oscillating cylinder steam engine The

steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...

needs to be fed into the end of the cylinder at just the right time in the cycle to push the

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder (engine), cylinder a ...

in the correct direction. In the other direction, the steam needs to be allowed to escape from the cylinder. As the

crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...

rotates, the piston rod moves up and down (or side to side in the case of a vertical cylinder) as well as in and out. Because the piston rod is rigid and the piston itself is long relative to its diameter, this causes the cylinder to rock, or "oscillate" on its special mounting (

). In the design usually found in a toy or model engine, a hole in the side of the cylinder (one at each end for a double-acting cylinder) and a pair of holes in the port block are arranged so that this rocking motion lines up the holes at the correct times, allowing steam to enter the cylinder in one direction and to escape into the atmosphere or condenser in the other direction.Roly Williams (2003-2010) ''Live Steam Toys - A Users Guide'', published by the author In full-size engines, the steam and exhaust ports are usually built into the pivot (

) mounting. However, separate valves may be provided, controlled by the oscillating motion. This allows the cutoff timing to be varied to enable expansive working. Alternatively, expansive working can also be provided by means of Woolf compounding, just as compactly if the two expansion stages are provided on either side of a single piston within a single cylinder, all arranged as a trunk engine (however, an oscillating cylinder engine does not benefit from the advantage of compactness that a trunk engine would otherwise provide, as it has that already from its own design features). Each approach to expansive working compromises the advantage of simplicity but still retains the advantage of compactness.

Reversing

An oscillating cylinder engine cannot be reversed by means of the valve linkage (as in a normal fixed cylinder) because there is none. Reversing of the engine can be achieved by reversing the steam connections between inlet and exhaust or, in the case of small engines, by shifting the trunnion pivot point so that the port in the cylinder lines up with a different pair of ports in the port face. In the latter case, the fixed port face is usually provided with three ports, the central one being the steam feed and the outer two being exhausts, only one of which being in use at any time, depending on the required direction of running.

Marine

Early proposals for marine use of oscillating steam engine were made already in the late 18th century. In 1822 the first iron-built steam ship,

Aaron Manby ''Aaron Manby'' was a landmark vessel in the science of shipbuilding as the first iron steamship to go to sea. She was built by Aaron Manby (1776–1850) at the Horseley Ironworks. She made the voyage to Paris in June 1822 under Captain (late ...

, was completed, using 80-hp oscillating engines. In 1827 Joseph Maudslay patented an independently developed marine oscillating engine, with an improved valve gear. More improvements were made by English engineer John Penn, followed by introduction of 3-cylinder version by Scottish

John Scott Russell John Scott Russell (9 May 1808, Parkhead, Glasgow – 8 June 1882, Ventnor, Isle of Wight) was a Scottish civil engineer, naval architecture, naval architect and shipbuilder who built ''SS Great Eastern, Great Eastern'' in collaboration with Is ...

in 1853. Early on shipbuilders considered the moving parts of the oscillating engine a hazard, inside the small spaces of a ship. However, later the popularity of the engine type grew and paddle steamers with engine of this type were built well into the 1860s with some reaching power over 1,600-hp.

Examples

References

{{Steam engine configurations Steam engines

Operation

Reversing

Marine

Examples

See also

References