Oscillating cylinder steam engine

Last updated December 31, 2023

A simple oscillating cylinder engine, part of a Mamod SE2 working steam model Rew7h13-976.jpg — A simple oscillating cylinder engine, part of a Mamod SE2 working steam model

An oscillating cylinder steam engine (also known as a wobbler in the US)^{[ citation needed ]} is a simple steam-engine design (proposed by William Murdoch at the end of 18th century) that requires no valve gear. Instead the cylinder rocks, or oscillates, as the crank moves the piston, pivoting in the mounting trunnion 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 engines are now mainly used in toys and models but, in the past, have been used in full-size working engines, mainly on ships and small stationary engines. 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

The steam needs to be fed into the end of the cylinder at just the right time in the cycle to push the piston in the correct direction. In the other direction, the steam needs to be allowed to escape from the cylinder. As the crankshaft 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 (trunnion). 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.^[1]

In full-size engines, the steam and exhaust ports are usually built into the pivot (trunnion) mounting. However, separate valves may be provided, controlled by the oscillating motion. This allows the cutoff timing to be varied to enable expansive working, as in, for example, the engine in the paddle ship PD Krippen. 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.^[2]

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, 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 in 1853.^[3]

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.^[3]

Examples

Examples of oscillating cylinder steam engines

A reversible oscillating cylinder on a toy steam engine. The trunnion is shifted by an eccentric on the lever.
A typical small stationary oscillating cylinder engine
Model of a marine oscillating steam engine designed by Joseph Maudslay, clearly showing how the cylinders pivot on the trunnions, through which the steam is passed.

Related Research Articles

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 and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder.

<span class="mw-page-title-main">Steam engine</span> Engine that uses steam to perform mechanical work

A steam engine is a heat engine that performs 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. This pushing force can be transformed, by a connecting rod and crank, into rotational force for work. The term "steam engine" is generally applied only to reciprocating engines as just described, not to the steam turbine. Steam engines are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants, such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.

<span class="mw-page-title-main">Two-stroke engine</span> Internal combustion engine type

A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during one power cycle, this power cycle being completed in one revolution of the crankshaft. A four-stroke engine requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

<span class="mw-page-title-main">Poppet valve</span> Type of valve

A poppet valve is a valve typically used to control the timing and quantity of gas or vapor flow into or out of an engine, but with many other applications.

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 gear. It is sometimes referred to as the "motion".

<span class="mw-page-title-main">Compound steam engine</span> Steam engine where steam is expanded in stages

A compound steam engine unit is a type of steam engine where steam is expanded in two or more stages. A typical arrangement for a compound engine is that the steam is first expanded in a high-pressure (HP) cylinder, then having given up heat and losing pressure, it exhausts directly into one or more larger-volume low-pressure (LP) cylinders. Multiple-expansion engines employ additional cylinders, of progressively lower pressure, to extract further energy from the steam.

The Walschaerts valve gear is a type of valve gear used to regulate the flow of steam to the pistons in steam locomotives, invented by Belgian railway engineer Egide Walschaerts in 1844. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. It was extensively used in steam locomotives from the late 19th century until the end of the steam era.

The Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear that was widely used throughout the world for various kinds of steam engines. It is named after Robert Stephenson but was invented by his employees.

In a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed. On a steam locomotive, the cutoff is controlled by the reversing gear.

A swing-piston engine is a type of internal combustion engine in which the pistons move in a circular motion inside a ring-shaped "cylinder", moving closer and further from each other to provide compression and expansion. Generally two sets of pistons are used, geared to move in a fixed relationship as they rotate around the cylinder. In some versions the pistons oscillate around a fixed center, as opposed to rotating around the entire engine. The design has also been referred to as a oscillating piston engine, vibratory engine when the pistons oscillate instead of rotate, or toroidal engine based on the shape of the "cylinder".

<span class="mw-page-title-main">Uniflow steam engine</span> Type of steam engine

The uniflow type of steam engine uses steam that flows in one direction only in each half of the cylinder. Thermal efficiency is increased by having a temperature gradient along the cylinder. Steam always enters at the hot ends of the cylinder and exhausts through ports at the cooler centre. By this means, the relative heating and cooling of the cylinder walls is reduced.

Piston valves are one form of valve used to control the flow of steam within a steam engine or locomotive. They control the admission of steam into the cylinders and its subsequent exhausting, enabling a locomotive to move under its own power. The valve consists of two piston heads on a common spindle moving inside a steam chest, which is essentially a mini-cylinder located either above or below the main cylinders of the locomotive.

An expansion valve is a device in steam engine valve gear that improves engine efficiency. It operates by closing off the supply of steam early, before the piston has travelled through its full stroke. This cut-off allows the steam to then expand within the cylinder. This expanding steam is still sufficient to drive the piston, even though its pressure decreases as it expands. As less steam is supplied in the shorter time for which the valve is open, use of the expansion valve reduces the steam consumed and thus the fuel required. The engine may deliver two-thirds of the work, for only one-third of the steam.

Cyldon was the brand name for a range of model stationary steam engines, manufactured in Enfield, Middlesex, England between 1947 and 1951 by Sydney S Bird & Sons. The name Cyldon was an amalgamation of Sydney Bird's two son's names Cyril and Donald.

A marine steam engine is a steam engine that is used to power a ship or boat. This article deals mainly with marine steam engines of the reciprocating type, which were in use from the inception of the steamboat in the early 19th century to their last years of large-scale manufacture during World War II. Reciprocating steam engines were progressively replaced in marine applications during the 20th century by steam turbines and marine diesel engines.

A model steam engine is a small steam engine not built for serious use. Often they are built as an educational toy for children, in which case it is also called a toy steam engine, or for live steam enthusiasts. Between the 18th and early 20th centuries, demonstration models were also in use at universities and engineering schools, frequently designed and built by students as part of their curriculum.

A return connecting rod, return piston rod or double piston rod engine or back-acting engine is a particular layout for a steam engine.

High-speed steam engines were one of the final developments of the stationary steam engine. They ran at a high speed, of several hundred rpm, which was needed by tasks such as electricity generation.

A bash valve is a valve within a piston engine, used to control the admission of the working fluid. They are directly actuated valves, operated by contact between the piston and the valve tip.

The Willans engine or central valve engine was a high-speed stationary steam engine used mainly for electricity generation around the start of the 20th century.

References

↑ Roly Williams (2003-2010) Live Steam Toys - A Users Guide, published by the author
↑ Griffiths, Denis (1997). Steam at Sea. Conway Maritime Press. ISBN 0-85177-666-3.
1 2 Winchester, Clarence, ed. (1936-05-12) [Original publication date of the magazine]. "Oscillating Paddle Engines - Shipping Wonders of the World". www.shippingwondersoftheworld.com. Issue number 14 of a magazine "Shipping Wonders of the World". Amalgamated Press . Retrieved 2023-03-07.

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[LSTUG-1] Roly Williams (2003-2010) Live Steam Toys - A Users Guide, published by the author

[Griffiths-2] Griffiths, Denis (1997). Steam at Sea. Conway Maritime Press. ISBN 0-85177-666-3.

[:0-3] 1 2 Winchester, Clarence, ed. (1936-05-12) [Original publication date of the magazine]. "Oscillating Paddle Engines - Shipping Wonders of the World". www.shippingwondersoftheworld.com. Issue number 14 of a magazine "Shipping Wonders of the World". Amalgamated Press . Retrieved 2023-03-07.

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