Single- and double-acting cylinders
In mechanical engineering, the cylinders of reciprocating engines are often classified by whether they are single- or double-acting, depending on how the working fluid acts on the piston.
Single-acting
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, springs, 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 almost universal in internal combustion engines (e.g. petrol and diesel engines) and are also used in many external combustion engines such as Stirling engines and some steam engines. They are also found in pumps and hydraulic rams.
Double-acting
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
Steam engines
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
Some of the later steam engines, the high-speed steam engines, used single-acting pistons of a new design. The crosshead 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 effective crankcase lubrication system.
Small models and toys often use single-acting cylinders for the above reason but also to reduce manufacturing costs.
Internal combustion engines
In contrast to steam engines, nearly all
Their pistons are usually
Crankcase compression two-stroke engines
Small petrol
Double-acting internal combustion engines
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 consistently compressive along the connecting rod, allowed for tighter bearing clearances.
Extremely large gas engines were also built as
Double-acting cylinders have been infrequently used for internal combustion engines since, although Burmeister & 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 MV Amerika (United Baltic Co.) in 1929.[3][4] The two B&W SCDA engines fitted to the MV Stirling Castle in 1937 produced 24,000 hp each.
USS Pompano
In 1935 the US submarine
Hydraulic cylinders
A hydraulic cylinder is a mechanical
Footnotes
- ^ The pressure of around 30 psi (2 bar) was low by today's standard and only "high" in comparison to Watt engines.
- trunk pistonis familiar from internal combustion engines today.
- ^ Alden[5] gives these as the Porpoise, Shark and Perch classes. Wikipedia's article considers them the P-1, P-3 & P-5 sub-types of a single Porpoise class[circular reference]
References
- ISBN 0-521-45834-X.
- ^ Hawkins, Nehemiah (1897). New Catechism of the Steam Engine. New York: Theo Audel. pp. 110–113.
- ISBN 9781107672932.
- ^ "Amazing Airplane Motor Doubles The Power", Popular Mechanics, September 1932 cutaway drawing of double action aircraft engine
- ^ ISBN 0-85368-203-8.
- ^ a b Alden (1979), pp. 65, 210.
- ^ Alden (1979), p. 210.