![<span class="mw-page-title-main">Piston</span> Machine component used to compress or contain expanding fluids in a cylinder](https://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Piston_of_DAT_engine.jpg/320px-Piston_of_DAT_engine.jpg)
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">Reciprocating engine</span> Engine utilising one or more reciprocating pistons](https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Four_stroke_engine_diagram.jpg/320px-Four_stroke_engine_diagram.jpg)
A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the Stirling engine for niche applications. Internal combustion engines are further classified in two ways: either a spark-ignition (SI) engine, where the spark plug initiates the combustion; or a compression-ignition (CI) engine, where the air within the cylinder is compressed, thus heating it, so that the heated air ignites fuel that is injected then or earlier.
![<span class="mw-page-title-main">Steam engine</span> Engine that uses steam to perform mechanical work](https://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/JamesWattEngine.jpg/320px-JamesWattEngine.jpg)
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 most commonly applied to reciprocating engines as just described, although some authorities have also referred to the steam turbine and devices such as Hero's aeolipile as "steam engines". The essential feature of steam engines is that they 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](https://upload.wikimedia.org/wikipedia/commons/3/33/Two-Stroke_Engine.gif)
A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston in one revolution of the crankshaft. A four-stroke engine requires four strokes of the piston to complete a power cycle in 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">Valve gear</span> Mechanism for controlling steam flow in a reciprocating steam engine.](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d7/Walschearts_valve_gear.jpg/320px-Walschearts_valve_gear.jpg)
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](https://upload.wikimedia.org/wikipedia/commons/8/8a/Triple_expansion_engine_animation.gif)
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.
![<span class="mw-page-title-main">Walschaerts valve gear</span> Type of valve gear](https://upload.wikimedia.org/wikipedia/commons/thumb/1/10/60163_Tornado_motion.jpg/320px-60163_Tornado_motion.jpg)
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.
![<span class="mw-page-title-main">Stephenson valve gear</span> Simple design of valve gear](https://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Black_5_George_Stephenson_7_%285441137329%29.jpg/320px-Black_5_George_Stephenson_7_%285441137329%29.jpg)
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](https://upload.wikimedia.org/wikipedia/commons/4/4a/Uniflow_steam_engine.gif)
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.
![<span class="mw-page-title-main">Piston valve (steam engine)</span> Form of valve within a steam engine or locomotive](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Cylinder_and_piston_valve_%28New_Catechism_of_the_Steam_Engine%2C_1904%29.jpg/320px-Cylinder_and_piston_valve_%28New_Catechism_of_the_Steam_Engine%2C_1904%29.jpg)
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.
![<span class="mw-page-title-main">Expansion valve (steam engine)</span>](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Cross_compound_engine%2C_plan_section_%28Heat_Engines%2C_1913%29.jpg/320px-Cross_compound_engine%2C_plan_section_%28Heat_Engines%2C_1913%29.jpg)
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.
![<span class="mw-page-title-main">Cyldon</span> English brand of model steam engines](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Cyldon_logo.png/320px-Cyldon_logo.png)
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.
![<span class="mw-page-title-main">Marine steam engine</span> Steam engine that is used to power a ship or boat](https://upload.wikimedia.org/wikipedia/commons/thumb/7/74/Popular_Science_Dec_1918_p23_-_Ship_Emergency_Steam_Cutoff_Valves.JPG/320px-Popular_Science_Dec_1918_p23_-_Ship_Emergency_Steam_Cutoff_Valves.JPG)
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.
![<span class="mw-page-title-main">Model steam engine</span> Steam engine used as a demonstration model](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Maerklin_Dampfmaschine1915_cropped.jpg/320px-Maerklin_Dampfmaschine1915_cropped.jpg)
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.
![<span class="mw-page-title-main">Return connecting rod engine</span>](https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Trevithick_high_pressure_engine_of_1806.jpg/320px-Trevithick_high_pressure_engine_of_1806.jpg)
A return connecting rod, return piston rod or double piston rod engine or back-acting engine is a particular layout for a steam engine.
![<span class="mw-page-title-main">High-speed steam engine</span> Steam engine designed to run at comparatively high speed](https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/George_Street_Mills_-_the_third_engine_-_geograph.org.uk_-_729965.jpg/320px-George_Street_Mills_-_the_third_engine_-_geograph.org.uk_-_729965.jpg)
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.
![<span class="mw-page-title-main">Willans engine</span>](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Willans_and_Robinson_engine_%28Rankin_Kennedy%2C_Electrical_Installations%2C_Vol_III%2C_1903%29.jpg/320px-Willans_and_Robinson_engine_%28Rankin_Kennedy%2C_Electrical_Installations%2C_Vol_III%2C_1903%29.jpg)
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.