A throttle is the mechanism by which fluid flow is managed by the constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases, but decreased; the term throttle has come to refer, informally, to any mechanism by which the power or speed of an engine is regulated, such as a car's accelerator pedal. What is termed a throttle is called a thrust lever for jet engine powered aircraft. For a steam engine, the steam valve that sets the engine speed/power is known as a regulator. In an internal combustion engine, the throttle is a means of controlling an engine's power by regulating the amount of fuel or air entering the engine. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle, accelerator, or gas pedal. For a gasoline engine, the throttle most regulates the amount of air and fuel allowed to enter the engine. For a GDI engine, the throttle regulates the amount of air allowed to enter the engine; the throttle of a diesel, when present, regulates the air flow into the engine.
The throttle pedal or lever acts via a direct mechanical linkage. Technically it means, that the butterfly valve of the throttle is operated by means of an arm piece, loaded by a spring; this arm is directly linked to the accelerator cable, operates in accordance with the driver, who hits it. The further the pedal is pushed, the wider the throttle valve opens. Modern engines of both types are drive-by-wire systems where sensors monitor the driver controls and in response a computerized system controls the flow of fuel and air; this means that the operator does not have direct control over the flow of air. The throttle on a gasoline engine is a butterfly valve. In a fuel-injected engine, the throttle valve is placed on the entrance of the intake manifold, or housed in the throttle body. In a carbureted engine, it is found in the carburetor; when a throttle is wide open, the intake manifold is at ambient atmospheric pressure. When the throttle is closed, a manifold vacuum develops as the intake drops below ambient pressure.
The power output of a diesel engine is controlled by regulating the quantity of fuel, injected into the cylinder. Because diesel engines do not need to control air volumes, they lack a butterfly valve in the intake tract. An exception to this generalization is newer diesel engines meeting stricter emissions standards, where such a valve is used to generate intake manifold vacuum, thereby allowing the introduction of exhaust gas to lower combustion temperatures and thereby minimize NOx production. In a reciprocating engine aircraft, the throttle control is a hand-operated lever or knob, it controls the engine power output, which may or may not reflect in a change of RPM, depending on the propeller installation. Some modern internal combustion engines do not use a traditional throttle, instead relying on their variable intake valve timing system to regulate the airflow into the cylinders, although the end result is the same, albeit with less pumping losses. In fuel injected engines, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main.
The throttle body is located between the air filter box and the intake manifold, it is attached to, or near, the mass airflow sensor. An engine coolant line runs through it in order for the engine to draw intake air at a certain temperature and therefore with a known density; the largest piece inside the throttle body is the throttle plate, a butterfly valve that regulates the airflow. On many cars, the accelerator pedal motion is communicated via the throttle cable, mechanically connected to the throttle linkages, which, in turn, rotate the throttle plate. In cars with electronic throttle control, an electric actuator controls the throttle linkages and the accelerator pedal connects not to the throttle body, but to a sensor, which outputs a signal proportional to the current pedal position and sends it to the ECU; the ECU determines the throttle opening based on the accelerator pedal's position and inputs from other engine sensors such as the engine coolant temperature sensor. When the driver presses on the accelerator pedal, the throttle plate rotates within the throttle body, opening the throttle passage to allow more air into the intake manifold drawn inside by its vacuum.
A mass airflow sensor measures this change and communicates it to the ECU. The ECU increases the amount of fuel injected by the injectors in order to obtain the required air-fuel ratio. A throttle position sensor is connected to the shaft of the throttle plate to provide the ECU with information on whether the throttle is in the idle position, wide-open throttle position, or somewhere in between these extremes. Throttle bodies may contain valves and adjustments to control the minimum airflow during idle. In those units that are not "drive-by-wire", there will be a small solenoid driven valve, the Idle Air Control Valve, that the ECU uses to control the amount of
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or obstructing various passageways. Valves are technically fittings, but are discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure; the word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll. The simplest, ancient, valve is a hinged flap which drops to obstruct fluid flow in one direction, but is pushed open by flow in the opposite direction; this is called "checks" the flow in one direction. Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems. Valves have many uses, including controlling water for irrigation, industrial uses for controlling processes, residential uses such as on/off and pressure control to dish and clothes washers and taps in the home. Aerosols have a tiny valve built in. Valves are used in the military and transport sectors.
Valves are found in every industrial process, including water and sewage processing, power generation, processing of oil and petroleum, food manufacturing and plastic manufacturing and many other fields. People in developed nations use valves in their daily lives, including plumbing valves, such as taps for tap water, gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, poppet valves in car engines. In nature there are valves, for example one-way valves in veins controlling the blood circulation, heart valves controlling the flow of blood in the chambers of the heart and maintaining the correct pumping action. Valves may be operated manually, either by a handle, pedal or wheel. Valves may be automatic, driven by changes in pressure, temperature, or flow; these changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found are safety valves fitted to hot water systems or boilers.
More complex control systems using valves requiring automatic control based on an external input require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned and allowing control over a variety of requirements. Valves vary in form and application. Sizes range from 0.1 mm to 60 cm. Special valves can have a diameter exceeding 5 meters. Valve costs range from simple inexpensive disposable valves to specialized valves which cost thousands of US dollars per inch of the diameter of the valve. Disposable valves may be found in common household items including mini-pump dispensers and aerosol cans. A common use of the term valve refers to the poppet valves found in the vast majority of modern internal combustion engines such as those in most fossil fuel powered vehicles which are used to control the intake of the fuel-air mixture and allow exhaust gas venting. Valves may be classified into a number of basic types. Valves may be classified by how they are actuated: Hydraulic Pneumatic Manual Solenoid valve Motor The main parts of the most usual type of valve are the body and the bonnet.
These two parts form the casing. The valve's body is the outer casing of most or all of the valve that contains the internal parts or trim; the bonnet is the part of the encasing through which the stem passes and that forms a guide and seal for the stem. The bonnet screws into or is bolted to the valve body. Valve bodies are metallic or plastic. Brass, gunmetal, cast iron, alloy steels and stainless steels are common. Seawater applications, like desalination plants use duplex valves, as well as super duplex valves, due to their corrosion resistant properties against warm seawater. Alloy 20 valves are used in sulphuric acid plants, whilst monel valves are used in hydrofluoric acid plants. Hastelloy valves are used in high temperature applications, such as nuclear plants, whilst inconel valves are used in hydrogen applications. Plastic bodies are used for low pressures and temperatures. PVC, PP, PVDF and glass-reinforced nylon are common plastics used for valve bodies. A bonnet acts as a cover on the valve body.
It is semi-permanently screwed into the valve body or bolted onto it. During manufacture of the valve, the internal parts are put into the body and the bonnet is attached to hold everything together inside. To access internal parts of a valve, a user would take off the bonnet for maintenance. Many valves do not have bonnets. Many ball valves do not have bonnets since the valve body is put together in a different style, such as being screwed together at the middle of the valve body. Ports are passages. Ports are obstructed by disc to control flow. Valves most have 2 ports, but may have as many as 20; the valve is always connected at its ports to pipes or other components. Connection methods include threadings, compression fittings, cement, flanges, or welding. A handle is used to manually control a valve from outside the valve body. Automatically controlled valves do not have handles, but some may have a handle anyway to manually override automatic control, such as a stop-check valve. An actuator is a mechanism or device to automatically or remotely control
Compound steam engine
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 cylinder having given up heat and losing pressure, it exhausts directly into one or more larger-volume low-pressure cylinders. Multiple-expansion engines employ additional cylinders, of progressively lower pressure, to extract further energy from the steam. Invented in 1781, this technique was first employed on a Cornish beam engine in 1804. Around 1850, compound engines were first introduced into Lancashire textile mills. There are many compound systems and configurations, but there are two basic types, according to how HP and LP piston strokes are phased and hence whether the HP exhaust is able to pass directly from HP to LP or whether pressure fluctuation necessitates an intermediate "buffer" space in the form of a steam chest or pipe known as a receiver. In a single-expansion steam engine, the high-pressure steam enters the cylinder at boiler pressure through an inlet valve.
The steam pressure forces the piston down the cylinder. After the steam supply is cut off the trapped steam continues to expand, pushing the piston to the end of its stroke, where the exhaust valve opens and expels the depleted steam to the atmosphere, or to a condenser; this "cut-off" allows much more work to be extracted, since the expansion of the steam is doing additional work beyond that done by the steam at boiler pressure. An earlier cut-off increases the expansion ratio, which in principle allows more energy to be extracted and increases efficiency, but as the trapped steam expands its temperature drops; this temperature drop would occur if the cylinder were insulating so that no heat is released from the system. As a result, steam leaves at a lower temperature; the changing steam temperature alternately heats and cools the cylinder with every stroke and is a source of inefficiency which increases at higher expansion ratios. Beyond a certain point, further increasing the expansion ratio will decrease efficiency due to the increased heating and cooling.
A method to lessen the magnitude of this heating and cooling was invented in 1804 by British engineer Arthur Woolf, who patented his Woolf high pressure compound engine in 1805. In the compound engine, high-pressure steam from the boiler first expands in a high-pressure cylinder and enters one or more subsequent lower pressure cylinders; the complete expansion of the steam occurs across multiple cylinders and, as there is less expansion in each cylinder, less heat is lost by the steam in each. This reduces the magnitude of cylinder heating and cooling, making higher expansion ratios practical and increasing the efficiency of the engine. There are other advantages: as the temperature range is smaller, cylinder condensation is reduced. Loss due to condensation is restricted to the LP cylinder. Pressure difference is less in each cylinder so there is less steam leakage at the piston and valves; the turning moment is more uniform, so balancing is easier and a smaller flywheel may be used. Only the smaller HP cylinder needs to be built to withstand the highest pressure, which reduces the overall weight.
Components are subject to less strain, so they can be lighter. The reciprocating parts of the engine are lighter; the compound could be started at any point in the cycle, in the event of mechanical failure the compound could be reset to act as a simple, thus keep running. To derive equal work from lower-pressure steam requires a larger cylinder volume as this steam occupies a greater volume. Therefore, the bore, in rare cases the stroke as well, are increased in low-pressure cylinders, resulting in larger cylinders. Double-expansion engines expand the steam in two stages, but this does not imply that all such engines have two cylinders, they may have four cylinders working as two LP-HP pairs, or the work of the large LP cylinder can be split across two smaller cylinders, with one HP cylinder exhausting into either LP cylinder, giving a 3-cylinder layout where the cylinder and piston diameter of all three are about the same, making the reciprocating masses easier to balance. Two-cylinder compounds can be arranged as: Cross-compound – the cylinders are side by side Tandem compound – the cylinders are end to end, driving a common connecting rod Telescopic-compound – the cylinders are one inside the other Angle-compound – the cylinders are arranged in a vee and drive a common crank.
The adoption of compounding was widespread for stationary industrial units where the need was for increased power at decreasing cost, universal for marine engines after 1880. It was not used in railway locomotives where it was perceived as complicated and unsuitable for the harsh railway operating environment and limited space afforded by the loading gauge. Compounding was never common on British railways and not employed at all after 1930, but was used in a limited way in many other countries; the first successful attempt to fly a heavier-than-air fixed-wing aircraft on steam power occurred in 1933, when George and William Besler converted a Travel Air 2000 biplane to fly on a 150 hp angle-compound V-twin steam engine of their own design instead of the usual Curtiss OX-5 inline or radial aviation gasoline engine it would have used. It is a logical extension of the compound engine to split the expansion into yet more
A compound engine is an engine that has more than one stage for recovering energy from the same working fluid, with the exhaust from the first stage passing through the second stage, in some cases on to another subsequent stage or stages. Invented as a means of making steam engines more efficient, the compounding of engines by use of several stages has been used on internal combustion engines and continues to have niche markets there; the stages of a compound engine may be either of differing or of similar technologies, for example: In a turbo-compound engine, the exhaust gas from the cylinders passes through a turbine, the two stages being dissimilar. In a compound steam locomotive, the steam passes from the high-pressure cylinder or cylinders to the low-pressure cylinder or cylinders, the two stages being similar. In a triple-expansion steam engine, the steam passes through three successive cylinders of increasing size and decreasing pressure; such engines were the most common marine engines in the golden age of steam.
These examples and compound turbines are the main but not the only uses of compounding in engines, see below. A compound engine uses several stages to produce its output. Not all engines that use multiple stages are called compound engines. In particular, if an engine uses a stage purely to extract energy from the exhaust for some other purpose, notably for turbo charging, is not called a compound engine. Proposed engines that use a free piston engine to drive a turbine would not be called compound engines, as only the second stage produces output power. However, if a turbo compound engine is supercharged by feeding some of the shaft power back to the supercharger, as in some aircraft engines, it is still a compound engine. Usage of the terms supercharged and turbosupercharged has varied with time, for example the makers of the Wright R-3350 Duplex-Cyclone compound engine described it at the time as turbosupercharged, it is however a compound engine, a similar engine produced today would be described as supercharged rather than turbocharged.
The term compounding is a little less restrictive than compound engine. Large compound turbines are an application of compounding, as are the multiple rows of blades used in many gas turbines, but neither is referred to as a compound engine; the several sets of blades in a single turbine are better thought of as similar in principle to the uniflow steam engine than to compounding. Unlike the uniflow steam engine, which has found niche uses only, multiple row turbines have found enormous practical application. An engine that does not use compounding is referred to as a simple engine in the case of a steam locomotive, or more as a simple expansion engine in the case of a marine steam engine. Note however that in the case of any steam engine, simple engine can be used to mean one that does not use a condenser to generate negative pressure and so improve efficiency. Use of separate condensers for this purpose is one of the key features that distinguishes the Watt steam engine of 1765 from the Newcomen steam engine of 1712.
No ambiguity arises in the case of a steam locomotive, as in a condensing steam locomotive the condenser is not there to increase efficiency, may reduce efficiency in order to conserve water and reduce emissions. So for example the Metropolitan Railway A Class is in every sense a simple locomotive despite its condensers, the term simple engine applied to steam locomotives always in practice means one that does not use compounding, again irrespective of its use of condensers; the terms simple expansion locomotive and simple expansion engine are sometimes applied to locomotives to remove any possible confusion. The oldest examples of compound engines are compound steam engines. In 1805 Arthur Woolf patented the Woolf high pressure compound engine. Compounding was particular used on stationary steam engines, marine steam engines, on some but by no means all steam locomotives starting from the 1850s but not only in continental Europe. Three stage or triple expansion reciprocating steam engines, with three cylinders of increasing bore in line, were popular for steamship propulsion.
"Doctor" Alexander Carnegie Kirk, experimentally fitted his first triple expansion engine to a ship called Propontis in 1874. In 1881, Kirk installed a refined version of his engine in SS Aberdeen on Scotland; this ship proved the advantages of power and economy of the new engine, in commercial service between the United Kingdom and the Far East. The first warship to be so equipped was the Spanish warship Destructor, built on Clydeside, the first engine of this type used in ships of the Royal Navy was designed by J. W. Reed, who created the Reed water tube boiler. Other navies and commercial shipowners soon followed. Four-stage, or quadruple, expansion engines were used. Several classes of steam locomotive have existed in both simple and compound form, most when locomotives built as compound were converted to simple in order to gain power at the expense of efficiency, for example the majority of the NZR X class. Other conversions involved redesigning the details of the compounding, for example many compound locomotives designed by Alfred de Glehn and state of the art in their day were modified by André Chapelon to use his scheme.
Attempts have been made to build compound internal combustion engines with high-pressure and low-pressure cylinders but these have not met with much success. Examples include: Deutz 1879, Forest-Gallice 1888, Connelly 1888, Diesel 1897, Bales 1897, Babled 1903, Butler 1904, Eisenhuth 1904-7, Abbot 1910. More turbo-compounding has been applied to internal combust
James Watt was a Scottish inventor, mechanical engineer, chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world. While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines, he realised that contemporary engine designs wasted a great deal of energy by cooling and reheating the cylinder. Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power and cost-effectiveness of steam engines, he adapted his engine to produce rotary motion broadening its use beyond pumping water. Watt attempted to commercialise his invention, but experienced great financial difficulties until he entered a partnership with Matthew Boulton in 1775; the new firm of Boulton and Watt was highly successful and Watt became a wealthy man.
In his retirement, Watt continued to develop new inventions though none was as significant as his steam engine work. He developed the concept of horsepower, the SI unit of power, the watt, was named after him. James Watt was born on 19 January 1736 in a seaport on the Firth of Clyde, his father James Watt, was a shipwright, ship owner and contractor, served as the town's chief baillie, whilst his mother, Agnes Muirhead, came from a distinguished family and was well educated. Both were strong Covenanters. Watt's grandfather, Thomas Watt, was a mathematics teacher and baillie to the Baron of Cartsburn. Despite being raised by religious parents, he became a deist. Watt did not attend school regularly, he exhibited great manual dexterity, engineering skills and an aptitude for mathematics, while Latin and Greek failed to interest him. He is said to have suffered prolonged bouts of ill-health as a child; when he was eighteen, his mother died and his father's health began to fail. Watt travelled to London and was apprenticed as an instrument maker for a year returned to Scotland, settling in the major commercial city of Glasgow intent on setting up his own instrument-making business.
He made and repaired brass reflecting quadrants, parallel rulers, parts for telescopes, barometers, among other things. Because he had not served at least seven years as an apprentice, the Glasgow Guild of Hammermen blocked his application, despite there being no other mathematical instrument makers in Scotland. Watt was saved from this impasse by the arrival from Jamaica of astronomical instruments bequeathed by Alexander Macfarlane to the University of Glasgow, instruments that required expert attention. Watt was remunerated; these instruments were installed in the Macfarlane Observatory. Subsequently three professors offered him the opportunity to set up a small workshop within the university, it was initiated in 1757 and two of the professors, the physicist and chemist Joseph Black as well as the famed Adam Smith, became Watt's friends. At first he worked on maintaining and repairing scientific instruments used in the university, helping with demonstrations, expanding the production of quadrants.
In 1759 he formed a partnership with John Craig, an architect and businessman, to manufacture and sell a line of products including musical instruments and toys. This partnership lasted for the next six years, employed up to sixteen workers. Craig died in 1765. One employee, Alex Gardner took over the business, which lasted into the twentieth century. In 1764, Watt married his cousin Margaret Miller, with whom he had five children, two of whom lived to adulthood: James Jr. and Margaret. His wife died in childbirth in 1772. In 1777 he was married again, to Ann MacGregor, daughter of a Glasgow dye-maker, with whom he had two children: Gregory, who became a geologist and mineralogist, Janet. Ann died in 1832. Between 1777 and 1790 he lived in Birmingham. There is a popular story that Watt was inspired to invent the steam engine by seeing a kettle boiling, the steam forcing the lid to rise and thus showing Watt the power of steam; this story is told in many forms. James Watt of course did not invent the steam engine, as the story implies, but improved the efficiency of the existing Newcomen engine by adding a separate condenser.
This is difficult to explain to someone not familiar with concepts of heat and thermal efficiency. It appears that the story of Watt and the kettle was created by Watt's son James Watt Jr. and persists because it is easy for children to understand and remember. In this light it can be seen as akin to the story of Isaac Newton, the falling apple and his discovery of gravity. Although it is dismissed as a myth, like most good stories the story of James Watt and the kettle has a basis in fact. In trying to understand the thermodynamics of heat and steam James Watt carried out many laboratory experiments and his diaries record that in conducting these he used a kettle as a boiler to generate steam. In 1759 Watt's friend, John Robison, called his attention to the use of steam as a source of motive power; the design of the Newcomen engine, in use for 50 years for pumping water from mines, had hardly changed from its first implementation. Wat
A steam motor is a form of steam engine used for light locomotives. They represented one of the final developments of the steam locomotive, in the final decades of the widespread use of steam power; the principle of the steam motor is to use the developments of the high-speed steam engine, to apply them to light locomotives. Rather than a large conventional locomotive having only two cylinders, rotating at the speed of the driving wheels, the steam motor uses several small cylinders geared to run at high speeds. With all other factors remaining the same, doubling the speed of a piston engine doubles its power; the steam motor allowed light engines to be used. As many of the engine's performance losses remain constant, or are related to the engine size, these small engines could be more efficient overall. All steam motors had the following characteristics: Small sizeMotors were of a standard size, according to the manufacturer's product line. Where greater power was required, multiple motors were used, one per bogie.
Enclosed crankshaft lubricationThe crankshaft and the valve gear, was enclosed within a crankcase that contained an oil sump. This provided a generous supply of lubrication and excluded dirt. Geared driveThis allows a high crankshaft speed. Although not all geared steam locomotives made use of this the US designs such as the Shay and the Climax, it was an essential part of the steam motor concept; the final drive of early Sentinel locomotives was by chain. Designs those by Abner Doble, preferred spur gears. Gear drives required the steam motor to be mounted low-down, alongside the axle. Other beneficial characteristics were found, but were not essential. Advanced valve gearThis was poppet valves driven by camshafts. In the steam motors built by Sentinel, the motor was derived from their advanced steam wagon design. Small driving wheelsIn a conventional steam locomotive, the'gear ratio' is set by the size of the driving wheels; as a steam motor uses a geared drive, the wheel size can be reduced. This makes for a lighter and more compact chassis by reducing the unsprung weight of large wheels.
Small wheels allow the motor to be mounted on a bogie within a passenger coach to form a railcar, rather than the large wheels being the size of a locomotive. These features give advantages: Higher efficiencyThis is owing to the high speed of the engines and the reduction gearing, but their other advanced design features. Reduced servicingThe use of oil-bath lubrication reduces the time spent in daily oiling. Reduced maintenanceThe use of oil-bath lubrication reduces the rate of wear, thus reducing the need for periodic maintenance; this is due to the exclusion of dirt, as well as the generous and reliable lubrication. Although other oil-bath systems on steam locomotives, such as the Bulleid chain-driven valve gear, gained a poor reputation for reliability, this was due to the difficulty of sealing such a large container. With the steam motor, only the motor's small crankcase was a sealed box. Simpler maintenanceMaintenance, when required, involves smaller components; these are easier to work on.
The motor may easily be removed in one piece for maintenance, either on-shed, or by return to the manufacturer. This allows a vehicle to be returned to service more by swapping motor units. Low manufacturing costComponents are manufactured in greater volume, as many designs of locomotive may be built around standardised motor designs; the machinery required to manufacture steam motors is smaller, thus less specialised and cheaper. Reduced hammer blowThe smoother drive of the geared motor, its multiple cylinders, reduced the dynamic effect of individual cylinder strokes. ArticulationWith multiple motors, there is no need for a single large frame to carry all of the driven wheels; this was an attractive feature for the Colombian locomotives, where a powerful locomotive was provided on a flexible chassis. As the driving wheels were small and articulated, there was no need for separate carrying axles. All wheels could be powered. Between 1901 and 1908, Ganz Works of Budapest and de Dion-Bouton of Paris collaborated to build a number of railcars for the Hungarian State Railways together with units with de Dion-Bouton boilers, Ganz steam motors and equipments, Raba carriages built by the Raba Hungarian Wagon and Machine Factory in Győr.
In 1908, the Borzsavölgyi Gazdasági Vasút, a narrow-gauge railway in Carpathian Ruthenia, purchased five railcars from Ganz and four railcars from the Hungarian Royal State Railway Machine Factory with de Dion-Bouton boilers. The Ganz company started to export steam motor railcars to the United Kingdom, Canada, Japan and Bulgaria; the first multiple-cylinder locomotive to demonstrate some of the principles of the steam motor was the Midland Railway's Paget locomotive of 1907. This was one of many attempts to build a balanced locomotive, so avoiding the problems of hammer blow, it followed contemporary advanced stationary engine practice in using single-acting cylinders. The locomotive has been variously described as either inspired by, or using, the design of the Willans engine that represented the peak of steam engine design at this time. In fact, the rotary valves used for the locomotive were different from the Willans' characteristic central valve spindle though they did both use single-acting trunk pistons.
Eight cylinders were used, two driving the front axle of the three driving axles, four the middle axle and two the rear axle. All three axles were coupled by external coupling rods
Single- and double-acting cylinders
Reciprocating engine cylinders are classified by whether they are single- or double-acting, depending on how the working fluid acts on the piston. A single-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts on one side of the piston only. A single-acting cylinder relies on the load, other cylinders, or the momentum of a flywheel, to push the piston back in the other direction. Single-acting cylinders are found in most kinds of reciprocating engine, they are universal in internal combustion engines and are used in many external combustion engines such as Stirling engines and some steam engines. They are found in pumps and hydraulic rams. A double-acting cylinder is a cylinder in which the working fluid acts alternately on both sides of the piston. In order to connect the piston in a double-acting cylinder to an external mechanism, such as a crank shaft, a hole must be provided in one end of the cylinder for the piston rod, this is fitted with a gland or "stuffing box" to prevent escape of the working fluid.
Double-acting cylinders are unusual in other engine types. Many hydraulic and pneumatic cylinders use them where it is needed to produce a force in both directions. A double-acting hydraulic cylinder has a port at each end, supplied with hydraulic fluid for both the retraction and extension of the piston. A double-acting cylinder is used where an external force is not available to retract the piston or it can be used where high force is required in both directions of travel. Steam engines use double-acting cylinders. However, early steam engines, such as atmospheric engines and some beam engines were single-acting; these transmitted their force through the beam by means of chains and an "arch head", as only a tension in one direction was needed. Where these were used for pumping mine shafts and only had to act against a load in one direction, single-acting designs remained in use for many years; the main impetus towards double-acting cylinders came when James Watt was trying to develop a rotative beam engine, that could be used to drive machinery via an output shaft.
With a single-cylinder engine, a double-acting cylinder gave a smoother power output. The high-pressure engine, as developed by Richard Trevithick, used double-acting pistons and became the model for most steam engines afterwards; some of the steam engines, the high-speed steam engines, used single-acting pistons of a new design. The crosshead became part of the piston, there was no longer any piston rod; this was for similar reasons to the internal combustion engine, as avoiding the piston rod and its seals allowed a more effective crankcase lubrication system. Small models and toys use single-acting cylinders for the above reason but to reduce manufacturing costs. In contrast to steam engines, nearly all internal combustion engines have used single-acting cylinders, their pistons are trunk pistons, where the gudgeon pin joint of the connecting rod is within the piston itself. This avoids the crosshead, piston rod and its sealing gland, but it makes a single-acting piston essential. This, in turn, has the advantage of allowing easy access to the bottom of the piston for lubricating oil, which has an important cooling function.
This avoids local overheating of rings. Small petrol two-stroke engines, such as for motorcycles, use crankcase compression rather than a separate supercharger or scavenge blower; this uses both sides of the piston as working faces, the lower side of the piston acting as a piston compressor to compress the inlet charge ready for the next stroke. The piston is still considered as single-acting; some early gas engines, such as Lenoir's original engines, from around 1860, were double-acting and followed steam engines in their design. Internal combustion engines soon switched to single-acting cylinders; this was for two reasons: as for the high-speed steam engine, the high force on each piston and its connecting rod was so great that it placed large demands upon the bearings. A single-acting piston, where the direction of the forces was compressive along the connecting rod, allowed for tighter bearing clearances. Secondly the need for large valve areas to provide good gas flow, whilst requiring a small volume for the combustion chamber so as to provide good compression, monopolised the space available in the cylinder head.
Lenoir's steam engine-derived cylinder was inadequate for the petrol engine and so a new design, based around poppet valves and a single-acting trunk piston appeared instead. Large gas engines were built as blowing engines for blast furnaces, with one or two large cylinders and powered by the burning of furnace gas; these those built by Körting, used double-acting cylinders. Gas engines require little or no compression of their charge, in comparison to petrol or compression-ignition engines, so the double-acting cylinder designs were still adequate, despite their narrow, convoluted passageways. Double-acting cylinders have been infrequently used for internal combustion engines since, although Burmeister & Wain made 2-stroke cycle double-acting diesels for marine propulsion before 1930; the first, of 7,000 hp, was fitted in the British MV Amerika in 1929. The two B&W SCDA engines fitted to the MV Stirling Castle in 1937 produced 24,000 hp each. In 1935 the US submarine USS Pompano was ordered as part of the Perch class Six boats were built, with three different diesel engine designs from different makers.
Pompano was fitted with H. O. R. 8-cylinder double-acting engines that were a licence-built version of the MAN auxiliary engine