Also known as a "Wobbler" in USA and possibly other countries.

An oscillating cylinder steam engine is a simple arrangement which does not require valves

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...

 to direct steam into and out of the cylinder

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

. Instead of valves, the entire cylinder rocks, or oscillates, such that one or more holes in the cylinder line up with holes in a fixed port face or in the pivot mounting (trunnion

Trunnion

A trunnion is a cylindrical protrusion used as a mounting and/or pivoting point. In a cannon, the trunnions are two projections cast just forward of the centre of mass of the cannon and fixed to a two-wheeled movable gun carriage...

).

Oscillating cylinder steam engine

Steam engine

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

s are mainly used in toys and models but have been used in full-size working engines, mainly on ships and small stationary engines

Stationary steam engine

Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars , agricultural engines used for ploughing or...

. 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 size, which makes them advantageous for use in ships. In full-size engines, the steam and exhaust ports are usually built into the pivot (trunnion) mounting.

Operation

The steam

Steam

Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

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

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

 in the correct direction. In the other direction, the steam needs to be allowed to escape into the atmosphere. As the crankshaft

Crankshaft

The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 rotates, the piston rod

Piston rod

In a piston engine, a piston rod joins a piston to a connecting rod.Many internal combustion engines, and in particular all current automobile engines, do not have true piston rods, and the term piston rod is often used as a synonym for connecting rod in the context of these engines.All engines...

 moves up and down (or side to side) as well as in and out. Because the piston rod is not flexible, 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

Double-acting cylinder

A double-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts alternately on both sides of the piston. This is in contrast to a single-acting cylinder, in which the working fluid acts in one direction only....

) and a pair of holes in the mounting 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

Condenser (heat transfer)

In systems involving heat transfer, a condenser is a device or unit used to condense a substance from its gaseous to its liquid state, typically by cooling it. In so doing, the latent heat is given up by the substance, and will transfer to the condenser coolant...

 in the other direction..

Reversing

Reversing of the engine can be achieved by reversing the steam connections between inlet and exhaust or by shifting the pivot point so that the hole in the cylinder lines up with a different pair of holes in the port face.

Examples

See also

• Elbow engine
  Elbow engine
  An elbow engine is a piston-based engine typically fed by steam or compressed air to drive a flywheel and/or mechanical load. Although not commonly used today for practical purposes, it is still built by hobbyists for its uniqueness.- Principle of operation :...
  
  
• Carpet railway
  Carpet Railway
  A Birmingham Dribbler or carpet railway describes the very first model railways. It is a bit of a misnomer, as the railway featured a model live steam railway locomotive, but no track – the locomotive was simply run across the floor...
  
  – the 'Birmingham Dribbler' toy locomotives used this type of engine