1.piston:Pistons within a sectioned petrol engine A piston is a component of reciprocating engines, reciprocating pumps, gas compressors 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 cranshaft via a piston rod and!or connecting rod. In a pump, the function is reversed and force is transferred from the cranshaft to the piston for the purpose of compressing or e"ecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall. #ontents 1 Piston engines 1.1 Internal combustion engines 1.1.1 $run pistons.. 1.1.% #rosshead pistons.. 1.1.& 'lipper pistons 1.1.( )eflector pistons 1.% 'team engines % Pumps %.1 *or li+uids %.% *or gases & Air cannons ( 'ee also eferences /xternal lins Internal combustion engine piston, sectioned to show the gudgeon pin. $he piston of an internal combustion engine is acted upon by the pressure of the expanding combustion gases in the combustion chamber space at the top of the cylinder. cylinder. $his force then acts downwards through the connecting rod and onto the cranshaft. $he connecting rod is attached to the piston by a swivelling gudgeon pin 0': wrist pin2. $his pin is mounted within the piston: unlie the steam engine, there is no piston rod or crosshead 0except big two stroe engines2. $he pin itself is of hardened steel and is fixed in the piston, but free to move in the connecting rod. A few designs use a 3fully f loating3 design that is loose in both components. All pins must be prevented from moving sideways and the ends of the pin digging into the cylinder wall, usually by circlips. 4as sealing is achieved by the use of piston rings. $hese are a number of narrow iron rings, fitted loosely into grooves in the piston, "ust below the crown. $he rings are split at a point in the rim, allowing them to press against the cylinder with a light spring pressure. $wo types types of ring are used: the upper rings have solid faces and provide gas sealing5 lower rings have narrow edges and a -shaped profile, to act as oil scrapers. $here are many proprietary and detail design features associated with piston rings.
Pistons are cast from aluminium alloys. *or better strength and fatigue life, some racing pistons may be forged instead. /arly pistons were of cast iron, but there were obvious benefits for engine balancing if a lighter alloy could be used. $o produce pistons that could survive engine combustion temperatures, it was necessary to develop new alloys such as 6 alloy and 7iduminium, specifically for use as pistons. A few early gas engines had double-acting cylinders, but otherwise effectively all internal
combustion engine pistons are single-acting. $run pistons:$run piston for a modern diesel engine $run pistons are long, relative to their diameter. $hey act as both piston and also as a c ylindrical crosshead. As the connecting rod is angled for part of its rotation, there is also a side force that reacts along the side of the piston against the cylinder wall. A longer piston helps to support this. $run pistons have been a common design of piston since the early da ys of the reciprocating internal combustion engine. $hey were used for both petrol and diesel engines, although high speed engines have now adopted the lighter weight slipper piston. A characteristic of most trun pistons, particularly for diesel engines, is that they have a groove for an oil ring below the gudgeon pin, not "ust the rings between the gudgeon pin and crown. $he name 3trun piston3 derives from the 3trun engine3, an early design of marine steam engine. $o mae these more compact, they avoided the steam engine3s usual piston rod and separate crosshead and were instead the first engine design to place the gudgeon pin directly within the piston. 8therwise these trun engine pistons bore little resemblance to the trun piston: they were of extremely large diameter and were double-acting. $heir 3trun3 was a narrow c ylinder placed mounted in the centre of this piston. #rosshead pistons:9arge slow-speed )iesel engines may re+uire additional support for the side forces on the piston. $hese engines typically use crosshead pistons. $he main piston has a large piston rod extending downwards from the piston to what is effectively a second smaller-diameter piston. $he main piston is responsible for gas sealing and carries the piston rings. $he smaller piston is purely a mechanical guide. It runs within a small cylinder as a trun guide and also carries the gudgeon pin. ecause of the additional weight of these pistons, they are not used for high-speed engines. 'lipper piston:A slipper piston is a piston for a petrol engine that has been reduced in si;e and weight as much as possible. In the extreme case, they are reduced to the piston crown, support for the piston rings, and "ust enough of the piston sirt remaining to leave two lands so as to stop the piston rocing in the bore. $he sides of the piston sirt around the gudgeon pin are reduced away from the cylinder wall. $he purpose is mostly to reduce the reciprocating mass, thus maing it easier to balance the engine and so permit high speeds. A secondary benefit may be some reduction in friction with the cylinder wall, however as most of this is due to the parts of the piston that are left behind, the benefit is minor.
)eflector pistons:$wo-stroe deflector piston )eflector pistons are used in two-stroe engines with crancase compression, where the gas flow within the cylinder must be carefully directed in order to provide efficient scavenging.
?uch effort, and man y different designs of piston crown, went into developing improved scavenging. $he crowns developed from a simple rib to a large asymmetric bulge, usually with a steep face on the inlet side and a gentle curve on the exhaust.
)espite this, cross scavenging was never as effective as hoped. ?ost engines today use 'chnuerle porting instead. $his places a pair of transfer ports in the sides of the cylinder and encourages gas flow to rotate around a vertical axis, rather than a hori;ontal axis.=%> 'team engines:#ast-iron steam engine piston, with a metal piston ring spring-loaded against the cylinder wall. 'team engines are usually double-acting 0i.e. steam pressure acts alternately on each side of the piston2 and the admission and release of steam is controlled by slide valves, piston valves or poppet valves. #onse+uently, steam engine pistons are nearly always comparatively thin discs: their diameter is several times their thicness. 08ne exception is the trun engine piston, shaped more lie those in a modern internal-combustion engine.2
@../arly 0c. 1&B2 piston for a beam engine. $he piston seal is made by turns of wrapped rope. Pumps:Piston pumps can be used to move li+uids or compress gases. *or li+uids=edit> ?ain article: eciprocating pump *or gases=edit> ?ain article: eciprocating compressor Air cannons=edit>
$his article contains embedded lists that may be poorly defined, unverified or indiscriminate. Please help to clean it up to meet Air gun 1. Piston:Pistons within a sectioned petrol engine A piston is a component of reciprocating engines, reciprocating pumps, gas compressors 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 cranshaft via a piston rod and!or connecting rod. In a pump, the function is reversed and force is transferred from the cranshaft to
the piston for the purpose of compressing or e"ecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall. #ontents 1 Piston engines 1.1 Internal combustion engines 1.1.1 $run pistons.. 1.1.% #rosshead pistons.. 1.1.& 'lipper pistons 1.1.( )eflector pistons 1.% 'team engines % Pumps %.1 *or li+uids %.% *or gases & Air cannons ( 'ee also eferences /xternal lins Internal combustion engine piston, sectioned to show the gudgeon pin. $he piston of an internal combustion engine is acted upon by the pressure of the expanding combustion gases in the combustion chamber space at the top of the cylinder. $his force then acts downwards through the connecting rod and onto the cranshaft. $he connecting rod is attached to the piston by a swivelling gudgeon pin 0': wrist pin2. $his pin is mounted within the piston: unlie the steam engine, there is no piston rod or crosshead 0except big two stroe engines2. $he pin itself is of hardened steel and is fixed in the piston, but free to move in the connecting rod. A few designs use a 3fully f loating3 design that is loose in both components. All pins must be prevented from moving sideways and the ends of the pin digging into the cylinder wall, usually by circlips. 4as sealing is achieved by the use of piston rings. $hese are a number of narrow iron rings, fitted loosely into grooves in the piston, "ust below the crown. $he rings are split at a point in the rim, allowing them to press against the cylinder with a light spring pressure. $wo types of ring are used: the upper rings have solid faces and provide gas sealing5 lower rings have narrow edges and a -shaped profile, to act as oil scrapers. $here are many proprietary and detail design features associated with piston rings.
Pistons are cast from aluminium alloys. *or better strength and fatigue life, some racing pistons may be forged instead. /arly pistons were of cast iron, but there were obvious benefits for engine balancing if a lighter alloy could be used. $o produce pistons that could survive engine combustion temperatures, it was necessary to develop new alloys such as 6 alloy and 7iduminium, specifically for use as pistons. A few early gas engines had double-acting cylinders, but otherwise effectively all internal combustion engine pistons are single-acting. $run pistons:$run piston for a modern diesel engine $run pistons are long, relative to their diameter. $hey act as both piston and also as a c ylindrical crosshead. As the connecting rod is angled for part of its rotation, there is also a side force that reacts along the side of the piston against the cylinder wall. A longer piston helps to support this.
$run pistons have been a common design of piston since the early da ys of the reciprocating internal combustion engine. $hey were used for both petrol and diesel engines, although high speed engines have now adopted the lighter weight slipper piston. A characteristic of most trun pistons, particularly for diesel engines, is that they have a groove for an oil ring below the gudgeon pin, not "ust the rings between the gudgeon pin and crown. $he name 3trun piston3 derives from the 3trun engine3, an early design of marine steam engine. $o mae these more compact, they avoided the steam engine3s usual piston rod and separate crosshead and were instead the first engine design to place the gudgeon pin directly within the piston. 8therwise these trun engine pistons bore little resemblance to the trun piston: they were of extremely large diameter and were double-acting. $heir 3trun3 was a narrow c ylinder placed mounted in the centre of this piston. #rosshead pistons:9arge slow-speed )iesel engines may re+uire additional support for the side forces on the piston. $hese engines typically use crosshead pistons. $he main piston has a large piston rod extending downwards from the piston to what is effectively a second smaller-diameter piston. $he main piston is responsible for gas sealing and carries the piston rings. $he smaller piston is purely a mechanical guide. It runs within a small cylinder as a trun guide and also carries the gudgeon pin. ecause of the additional weight of these pistons, they are not used for high-speed engines. 'lipper piston:A slipper piston is a piston for a petrol engine that has been reduced in si;e and weight as much as possible. In the extreme case, they are reduced to the piston crown, support for the piston rings, and "ust enough of the piston sirt remaining to leave two lands so as to stop the piston rocing in the bore. $he sides of the piston sirt around the gudgeon pin are reduced away from the cylinder wall. $he purpose is mostly to reduce the reciprocating mass, thus maing it easier to balance the engine and so permit high speeds. A secondary benefit may be some reduction in friction with the cylinder wall, however as most of this is due to the parts of the piston that are left behind, the benefit is minor.
)eflector pistons:$wo-stroe deflector piston )eflector pistons are used in two-stroe engines with crancase compression, where the gas flow within the cylinder must be carefully directed in order to provide efficient scavenging. ?uch effort, and man y different designs of piston crown, went into developing improved scavenging. $he crowns developed from a simple rib to a large asymmetric bulge, usually with a steep face on the inlet side and a gentle curve on the exhaust. )espite this, cross scavenging was never as effective as hoped. ?ost engines today use 'chnuerle porting instead. $his places a pair of transfer ports in the sides of the cylinder and encourages gas flow to rotate around a vertical axis, rather than a hori;ontal axis.=%> 'team engines:#ast-iron steam engine piston, with a metal piston ring spring-loaded against the cylinder wall.
'team engines are usually double-acting 0i.e. steam pressure acts alternately on each side of the piston2 and the admission and release of steam is controlled by slide valves, piston valves or poppet valves. #onse+uently, steam engine pistons are nearly always comparatively thin discs: their diameter is several times their thicness. 08ne exception is the trun engine piston, shaped more lie those in a modern internal-combustion engine.2
@../arly 0c. 1&B2 piston for a beam engine. $he piston seal is made by turns of wrapped rope. Pumps:Piston pumps can be used to move li+uids or compress gases. *or li+uids=edit> ?ain article: eciprocating pump *or gases=edit> ?ain article: eciprocating compressor Air cannons=edit>
$his article contains embedded lists that may be poorly defined, unverified or indiscriminate. Please help to clean it up to meet Air gun *lamethrower *ire piston *ruit press 7ydraulic cylinder Dnurling 'lide whistle
