Inmechanical engineering, thecylinders ofreciprocating engines are often classified by whether they are single- or double-acting, depending on how theworking fluid acts on thepiston.
Asingle-acting cylinder in areciprocating engine is acylinder in which theworking fluid acts on one side of thepiston only. A single-acting cylinder relies on the load, springs, other cylinders, or the momentum of aflywheel, to push the piston back in the other direction. Single-acting cylinders are found in most kinds of reciprocating engine. They are almost universal ininternal combustion engines (e.g.petrol anddiesel engines) and are also used in manyexternal combustion engines such asStirling engines and somesteam engines. They are also found in pumps andhydraulic rams.
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Adouble-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 acrank shaft, a hole must be provided in one end of the cylinder for the piston rod, and this is fitted with agland or "stuffing box" to prevent escape of the working fluid. Double-acting cylinders are common insteam engines but 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.
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Steam engines normally use double-acting cylinders. However, early steam engines, such asatmospheric engines and somebeam engines, were single-acting. These often 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 whenJames Watt was trying to develop arotative beam engine, that could be used to drive machinery via an output shaft.[1] Compared to a single-cylinder engine, a double-acting cylinder gave a smoother power output. The high-pressure engine,[i] as developed byRichard Trevithick, used double-acting pistons and became the model for most steam engines afterwards.
Some of the later steam engines, thehigh-speed steam engines, used single-acting pistons of a new design. Thecrosshead became part of the piston,[ii] and 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 effectivecrankcase lubrication system.
Small models and toys often use single-acting cylinders for the above reason but also to reduce manufacturing costs.
In contrast to steam engines, nearly allinternal combustion engines have used single-acting cylinders.
Their pistons are usuallytrunk 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 also makes a single-acting piston almost essential. This, in turn, has the advantage of allowing easy access to the bottom of the piston for lubricating oil, which also has an important cooling function. This avoids local overheating of the piston and rings.
Small petroltwo-stroke engines, such as for motorcycles, usecrankcase compression rather than a separate supercharger orscavenge 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, as only one of these facesproduces power.
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Some earlygas engines, such asLenoir's original engines, from around 1860, were double-acting and followedsteam 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 consistently compressive along the connecting rod, allowed for tighter bearing clearances.[2] 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 goodcompression, monopolised the space available in thecylinder head. Lenoir's steam engine-derived cylinder was inadequate for thepetrol engine and so a new design, based aroundpoppet valves and a single-actingtrunk piston appeared instead.
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Extremely large gas engines were also built asblowing engines forblast furnaces, with one or two extremely large cylinders and powered by the burning offurnace gas. These, particularly those built byKörting, used double-acting cylinders. Gas engines require little or no compression of their charge, in comparison to petrol orcompression-ignition engines, and 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, althoughBurmeister & Wain made 2-stroke cycle double-acting (2-SCDA) diesels for marine propulsion before 1930. The first, of 7,000 hp, was fitted in the British MVAmerika (United Baltic Co.) in 1929.[3][4] The two B&W SCDA engines fitted to theMV Stirling Castle in 1937 produced 24,000hp each.
In 1935 the US submarineUSSPompano was ordered as part of thePerch class[iii] Six boats were built, with three different diesel engine designs from different makers.Pompano was fitted with H.O.R. (Hooven-Owens-Rentschler) 8-cylinder double-acting engines that were alicence-built version of theMAN auxiliary engines of the cruiserLeipzig.[5] Owing to the limited space available within the submarines, eitheropposed-piston, or, in this case, double-acting engines were favoured for being more compact.Pompano's engines were a complete failure and were wrecked during trials before even leaving theMare Island Navy Yard.Pompano was laid up for eight months until 1938 while the engines were replaced.[5] Even then the engines were regarded as unsatisfactory and were replaced byFairbanks-Morse engines in 1942.[5] WhilePompano was still being built, theSalmon-class submarines were ordered. Three of these were built byElectric Boat, with a 9-cylinder development of the H.O.R. engine.[6] Although not as great a failure asPompano's engines, this version was still troublesome and the boats were later re-engined with the same single-actingGeneral Motors 16-248 V16 engines as their sister boats.[6] Other Electric Boat-constructed submarines of theSargo andSeadragon classes, as well as the first few of theGato class, were also built with these 9-cylinder H.O.R. engines, but later re-engined.[7]
Ahydraulic cylinder is a mechanicalactuator that is powered by a pressurised liquid, typically oil. It has many applications, notably in construction equipment (engineering vehicles),manufacturing machinery, and civil engineering.