HOME

TheInfoList



OR:

A poppet valve (also called mushroom valve) is a
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usually a disk shape on the end of a shaft known as a valve stem. The working end of this plug, the valve face, is typically ground at a 45° bevel to seal against a corresponding
valve seat The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical compon ...
ground into the rim of the chamber being sealed. The shaft travels through a valve guide to maintain its alignment. A pressure differential on either side of the valve can assist or impair its performance. In exhaust applications higher pressure against the valve helps to seal it, and in intake applications lower pressure helps open it. The poppet valve was invented in 1833 by American E.A.G. Young of the Newcastle and Frenchtown Railroad. Young had patented his idea, but the Patent Office fire of 1836 destroyed all records of it.


Etymology

The word
poppet In folk magic and witchcraft, a poppet (also known as poppit, moppet, mommet or pippy) is a doll made to represent a person, for casting spells on that person or to aid that person through magic. They are occasionally found lodged in chimneys ...
shares
etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
with " puppet": it is from the
Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English ...
''popet'' ("youth" or "doll"), from Middle French ''poupette'', which is a diminutive of ''poupée''. The use of the word ''poppet'' to describe a valve comes from the same word applied to
marionette A marionette (; french: marionnette, ) is a puppet controlled from above using wires or strings depending on regional variations. A marionette's puppeteer is called a marionettist. Marionettes are operated with the puppeteer hidden or revealed ...
s, which, like the poppet valve, move bodily in response to remote motion transmitted linearly. In the past, "puppet valve" was a synonym for ''poppet valve''; however, this usage of "puppet" is now obsolete.


Design

The poppet valve is fundamentally different from slide and oscillating valves; instead of sliding or rocking over a seat to uncover a port, the poppet valve lifts from the seat with a movement perpendicular to the plane of the port. The main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication. In most cases it is beneficial to have a "balanced poppet" in a direct-acting valve. Less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces. The solenoid coil has to counteract only the spring force. Poppet valves are best known for their use in internal combustion and steam engines, but are used in many industrial processes, from controlling the flow of
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modula ...
to isolating sterile air in the semiconductor industry. Presta and
Schrader valve The Schrader valve (also called American valve) is a type of pneumatic tire valve used on virtually every motor vehicle in the world today. The Schrader company, for which it was named, was founded in 1844 by August Schrader. The original Schra ...
s used on pneumatic tyres are examples of poppet valves. The Presta valve has no spring and relies on a pressure differential for opening and closing while being inflated. Poppet valves are employed extensively in the launching of
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, s ...
es from submarines. Many systems use compressed air to expel the torpedo from the tube, and the poppet valve recovers a large quantity of this air (along with a significant amount of seawater) in order to reduce the tell-tale cloud of bubbles that might otherwise betray the boat's submerged position.


Usage in internal combustion engines

Poppet valves are used in most piston engines to control the flow of intake and exhaust gasses through the cylinder head and into the combustion chamber. The side of the poppet valve which sits inside the combustion chamber is a flat disk, while the other side tapers from the disk shape to a thin cylindrical rod called a "valve stem".


Materials and durability

In a typical modern mass-production engines, the valves are solid and made from steel
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s. However some engines use hollow valves filled with
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
, to improve
heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
. Many modern engines use an aluminium cylinder head. Although this provides better heat transfer, it requires steel
valve seat The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical compon ...
inserts to be used; in older
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impur ...
cylinder heads, the valve seats are often part of the cylinder head. A gap of is present around the valve stem, therefore a ''valve stem seal'' is used to prevent combustion gasses escaping through this gap or oil being drawn into the combustion chamber. Typically, a rubber lip-type seal is used. A common symptom of worn valve guides and/or defective oil seals is a puff of blue smoke from the exhaust pipe at times of increased intake
manifold vacuum Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the ...
, such as when the throttle is abruptly closed. Historically, there were two major issues with valves, both of which have been solved by improvements in modern metallurgy. The first was that in early internal combustion engines, high wear rates of valves meant that a valve job to regrind the valves was required at regular intervals. Secondly, lead additives had been used in petrol (gasoline) since the 1920s, to prevent engine knocking and provide lubrication for the valves. Modern materials for the valves (such as stainless steel) and valve seats (such as stellite) allowed for leaded petrol to be phased out in many industrialised countries by the mid-1990s.


Actuation method

Early engines in the 1890s and 1900s used an "automatic" intake valve, which was opened by the vacuum in the combustion chamber and closed by a light spring. The exhaust valve had to be mechanically driven to open it against the pressure in the cylinder. Use of automatic valves simplified the mechanism, but
valve float Valve float is an adverse condition which can occur at high engine speeds when the poppet valves in an internal combustion engine valvetrain do not properly follow the closure phase of the cam lobe profile. This reduces engine efficiency and perform ...
limited the speed at which the engine could run, and by about 1905 mechanically operated inlet valves were increasingly adopted for vehicle engines. Mechanical operation is usually by pressing on the end of the valve stem, with a spring generally being used to return the valve to the closed position. At high engine speeds ( RPM), the weight of the valvetrain means the valve spring cannot close the valve as quickly enough, leading to
valve float Valve float is an adverse condition which can occur at high engine speeds when the poppet valves in an internal combustion engine valvetrain do not properly follow the closure phase of the cam lobe profile. This reduces engine efficiency and perform ...
or ''valve bounce''.
Desmodromic valve :''In general mechanical terms, the word ''desmodromic'' is used to refer to mechanisms that have different controls for their actuation in different directions.'' A desmodromic valve is a reciprocating engine poppet valve that is positively clo ...
s use a second rocker arm to mechanically close the valves (instead of using valve springs) and are sometimes used to avoid valve float in engines that operate at high RPM. In most mass-produced engines, the camshaft(s) control the opening of the valves, via several intermediate mechanisms (such as pushrods, roller rockers and valve lifters). The shape of the cams on the camshaft influence the
valve lift A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usual ...
and determine the timing of when the valves open.


Number and location of valves

Early flathead engines (also called ''L-head engines'') saw the valves located beside to the cylinder(s), in an "upside down" orientation parallel to the cylinder. Although this design made for simplified and cheap construction, the twisting path of the intake and exhaust gasses had major drawbacks for the airflow, which limited engine RPM and could cause the engine block to overheat under sustained heavy load. The flathead design evolved into intake over exhaust (IOE) engine, used in many early motorcycles and several cars. In an IOE engine, the intake valves were located directly above the cylinder (like the later ''overhead valve engines''), however the exhaust valve remains beside the cylinder in an upside down orientation. These designs were largely replaced by the overhead valve (OHV) engine between 1904 until late-1960s/early-to-mid 1970s, whereby the intake and exhaust valves are both located directly above the cylinder (with the camshaft located at the bottom of the engine). In turn, OHV engines were largely replaced by the overhead camshaft (OHC) engines between 1950s until 1980s. The location of the valves is broadly the same between OHV and OHC engines, however OHC engines saw the camshaft located to the top of the engine with the valves and OHC engines often have more valves per cylinder. Most OHC engines have an extra intake and an extra exhaust valve per cylinder (four-valve cylinder head), compared with the design of two valves per cylinder used by most OHV engines. However some OHC engines have used three or five valves per cylinder.


Usage in steam engines

James Watt was using poppet valves to control the flow of steam into the cylinders of his beam engines in the 1770s. A sectional illustration of Watt's beam engine of 1774 using the device is found in Thurston 1878:98, and Lardner (1840) provides an illustrated description of Watt's use of the poppet valve. When used in high-pressure applications, for example, as admission valves on steam engines, the same pressure that helps seal poppet valves also contributes significantly to the force required to open them. This has led to the development of the balanced poppet or double beat valve, in which two valve plugs ride on a common stem, with the pressure on one plug largely balancing the pressure on the other. In these valves, the force needed to open the valve is determined by the pressure and the difference between the areas of the two valve openings. Sickels patented a valve gear for double-beat poppet valves in 1842. Criticism was reported in the journal Science in 1889 of equilibrium poppet valves (called by the article the "double or balanced or American puppet valve") in use for paddle steamer engines, that by its nature it must leak 15 percent.Criticism by E.N. Dickerson in lecture to the Electric Club of New York 17/01/1889, reported by Science vol.13 No.314, Feb 8 1889 p.9
sciencemag.org
/ref> Poppet valves have been used on steam locomotives, often in conjunction with
Lentz Lentz is a Germanic languages, Germanic surname. People Notable people with the surname include: * Bryan Lentz (born 1964), attorney and former Pennsylvania legislator * Carl Lentz American pastor, former lead pastor of Hillsong Church NYC * Dani ...
or
Caprotti valve gear The Caprotti valve gear is a type of steam engine valve gear invented in the early 1920s by Italian architect and engineer Arturo Caprotti. It uses camshafts and poppet valves rather than the piston valves used in other valve gear. While basin ...
. British examples include: * LNER Class B12 *
LNER Class D49 The London and North Eastern Railway (LNER) D49 Class is a class of 4-4-0 steam locomotives designed by Nigel Gresley. They were named after fox hunts and shires. One, 246/62712 ''Morayshire'' has been preserved on the Bo'ness and Kinneil Rail ...
* LNER Class P2 * LMS Stanier Class 5 4-6-0 *
BR standard class 5 The British Railways Standard Class 5MT is one of the 12 Steam locomotives of British Railways#BR Standard Classes, standard classes of steam locomotive built by British Railways in the 1950s. It was essentially a development of the LMS Stanier ...
* BR standard class 8 71000 Duke of Gloucester.
Sentinel Waggon Works Sentinel Waggon Works Ltd was a British company based in Shrewsbury, Shropshire that made steam-powered lorries ( steam wagons), railway locomotives, and later, diesel engined lorries, buses and locomotives. History Alley & MacLellan, Se ...
used poppet valves in their steam wagons and steam locomotives. Reversing was achieved by a simple sliding camshaft system. Many locomotives in France, particularly those rebuilt to the designs of Andre Chapelon, such as the SNCF 240P, used Lentz oscillating-cam poppet valves, which were operated by the Walschaert valve gear the locomotives were already equipped with. The poppet valve was also used on the American Pennsylvania Railroad's T1
duplex locomotive A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive. The concept was first used in France in 1 ...
s, although the valves commonly failed because the locomotives were commonly operated in excess of , and the valves were not meant for the stresses of such speeds. The poppet valves also gave the locomotive a distinctive "chuffing" sound.


See also

* Double beat valve * Pneumatic valve springs *
Reed valve Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials (fiberglass or carbon f ...
*
Relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is re ...
*
Rotary valve A rotary valve (also called rotary-motion valve) is a type of valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes. The common stopcock is the simplest form of rot ...
* Sleeve valve *
Safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds ...


References

{{DEFAULTSORT:Poppet Valve Engine valves