A poppet valve (also called mushroom valve) is a valve typically
used to control the timing and quantity of gas or vapour flow into an
It consists of a hole, usually round or oval, and a tapered plug,
usually a disk shape on the end of a shaft also called a valve stem.
The portion of the hole where the plug meets with it is referred to as
the 'seat' or 'valve seat'. The shaft guides the plug portion by
sliding through a valve guide. In exhaust applications a pressure
differential helps to seal the valve and in intake valves a pressure
differential helps open it. The poppet valve was most likely invented
in 1833 by E.A.G. Young of the Newcastle and Frenchtown Railroad.
Young patented his idea but the Patent Office fire of 1836 destroyed
all records of it.
2.1 Internal combustion engine
2.2 Steam engine
3 See also
The word poppet shares etymology with "puppet": it is from the Middle
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 marionettes, 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. The valve stem moves up and down inside the passage called
guide, which is fitted in the engine-block. the head of the valve
called valve face, is generally grounded to 45 degrees angle, so as to
fit properly on the value seat in the block and prevent leakage
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.
This animation shows a pressure activated poppet valve (red), and a
cam activated poppet valve (blue), in a cylinder of an internal
Poppet valves in action at the top of the cylinder
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 used in many industrial processes, from controlling
the flow of milk to isolating sterile air in the semiconductor
industry. However, they are most well known for their use in internal
combustion and steam engines, as described below.
Presta and Schrader valves 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 torpedoes
from submarines. Many systems use compressed air to expel the torpedo
from the tube, and the poppet valve recovers 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
Internal combustion engine
Poppet valves are used in most piston engines to open and close the
intake and exhaust ports in the cylinder head. The valve is usually a
flat disk of metal with a long rod known as the 'valve stem' attached
to one side.
In early internal combustion engines (c1900) it was common that the
inlet valve was 'automatic', i.e. opened by the suction in the engine
and returned 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 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 revolutions per minute (RPM), the inertia of
the spring means it cannot respond quickly enough to return the valve
to its seat between cycles, leading to 'valve float' also known as
'valve bounce'. In this situation desmodromic valves can be used
which, being closed by a positive mechanical action instead of by a
spring, are able to cycle at the high speeds required in, for
instance, motorcycle and auto racing engines .
The engine normally operates the valves by pushing on the stems with
cams and cam followers. The shape and position of the cam determines
the valve lift and when and how quickly (or slowly) the valve is
opened. The cams are normally placed on a fixed camshaft which is then
geared to the crankshaft, running at half crankshaft speed in a
four-stroke engine. On high-performance engines, the camshaft is
movable and the cams have a varying height so, by axially moving the
camshaft in relation with the engine RPM, the valve lift also varies.
See variable valve timing.
For certain applications the valve stem and disk are made of different
steel alloys, or the valve stem may be hollow and filled with sodium
to improve heat transport and transfer. Although a better heat
conductor, an aluminium cylinder head requires steel valve seat
inserts, where a cast iron cylinder head would often have employed
integral valve seats in the past. Because the valve stem extends into
lubrication in the cam chamber, it must be sealed against blow-by to
prevent cylinder gases from escaping into the crankcase, even though
the stem to valve clearance is very small, typically
0.04-0.06 mm, so a rubber lip-type seal is used to ensure that
excessive oil is not drawn in from the crankcase on the induction
stroke, and that exhaust gas does not enter the crankcase on the
exhaust stroke. Worn valve guides and/or defective oil seals can often
be diagnosed by a puff of blue smoke from the exhaust pipe on
releasing the accelerator pedal after allowing the engine to overrun,
when there is high manifold vacuum. Such a condition occurs when
In multi-valve engines, the conventional two-valves-per-cylinder setup
is complemented by a minimum of an extra intake valve (three-valve
cylinder head) or, more commonly, with an extra intake and an extra
exhaust valve (four-valve cylinder head), the latter meaning higher
RPM are, theoretically, achievable. Five valve designs (with three
inlet and two exhaust valves) are also in use. More valves per
cylinder means improved gas flow and smaller reciprocating masses may
be achieved, leading to improved engine efficiency and, ultimately,
higher power output and better fuel economy. Multivalve engines also
allow for a centrally located spark plug, which improves combustion
efficiency and reduces detonation.
In very early engine designs the valves were 'upside down' in the
block, parallel to the cylinders. This was the so-called L-head engine
design, because of the shape of the cylinder and combustion chamber,
also called 'flathead engine' as the top of the cylinder head was
flat. The term preferred outside America (though occasionally used
there too) was sidevalve; hence, its use in the name of the UK-based
Ford Sidevalve Owners' Club. Although this design made for
simplified and cheap construction, it had two major drawbacks; the
tortuous path followed by the intake charge limited air flow and
effectively prevented speeds greater than 3600 RPM, and the path
of the exhaust through the block could cause overheating under
sustained heavy load. This design evolved into '
Intake Over Exhaust',
IOE or F-head, where the intake valve was in the head and the exhaust
valve was in the block; later both valves moved to the head.
In most such designs the camshaft remained relatively near the
crankshaft, and the valves were operated through pushrods and rocker
arms. This led to significant energy losses in the engine, but was
simpler, especially in a
V engine where one camshaft can actuate the
valves for both cylinder banks; for this reason, pushrod engine
designs have persisted longer in these configurations than others.
More modern designs have the camshaft on top of the cylinder head,
pushing directly on the valve stem (again through cam followers, also
known as tappets), a system known as overhead camshaft; if there is
just one camshaft, this is a single overhead cam or SOHC engine. Often
there are two camshafts, one for the intake and one for exhaust
valves, creating the dual overhead cam, or DOHC. The camshaft is
driven by the crankshaft - through gears, a chain or a timing belt.
In the early days of engine building, the poppet valve was a major
Metallurgy was lacking, and the rapid opening and closing of
valves against cylinder heads led to rapid wear. They would need to be
re-ground in a process known as a 'valve job'. Adding tetraethyllead
to the petrol reduced this problem somewhat, the lead coating the
valve seats would, in effect, lubricate the metal. In more modern
vehicles and properly machined older engines, valve seats may be made
of improved alloys such as stellite and the valves themselves of
stainless steel. These improvements have generally eradicated this
problem, and helped make unleaded fuel the norm.
Valve burn (overheating) is another problem. It causes excessive valve
wear and defective sealing, as well as engine knocking (the hot valve
causes the fuel to prematurely ignite). It can be solved by valve
cooling systems that use water or oil as a coolant. In high
performance or turbo charged engines sometimes sodium filled valve
stems are used. These valve stems then act as a heat pipe. A major
cause of burnt valves is a lack of valve clearance at the tappet; the
valve cannot completely close. This reduces its ability to conduct
heat to the cylinder head via the seat, and may allow hot combustion
gases to flow between the valve and its seat. Burnt valves will cause
a low compression in the affected cylinder and loss of power.
Valve from U.S. Patent 339,809. High pressure steam
enters at A and exits at B. The valve stem D moves up to open the
valve discs C
Valve on one of Chapelon's rebuilt 4-6-2
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.
Poppet valves have been used on steam locomotives, often in
conjunction with Lentz or Caprotti valve gear. British examples
LNER Class B12
LNER Class D49
LNER Class P2
LMS Stanier Class 5 4-6-0
BR standard class 5
BR standard class 8 71000 Duke of Gloucester.
Sentinel Waggon Works
Sentinel Waggon Works used poppet valves in their steam wagons and
steam locomotives. Reversing was achieved by a simple sliding camshaft
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 locomotives, although the valves commonly failed because the
locomotives were commonly operated in excess of 160 km/h
(100 mph), and the valves were not meant for the stresses of such
speeds. The poppet valves also gave the locomotive a distinctive
Double beat valve
^ A.L. Dyke (1921), Dyke's Automobile and Gasoline Encyclopedia
^ White, John H. (1979). A History of the American Locomotive. North
Chelmsford, MA: Courier Corporation. p. 145.
^ "'''Poppet''' at Merriam-Webster". Merriam-webster.com. Retrieved
^ "'''Puppet''' at Merriam-Webster". Merriam-webster.com. Retrieved
Puppet valve''' from 1913 Webster's dictionary".
Websters-online-dictionary.org. Archived from the original on
2006-02-21. Retrieved 2011-12-06.
^ "U.S. Patent No. 339809, "
Puppet Valve", issued April 13, 1886".
Patimg1.uspto.gov. Retrieved 2011-12-06.
^ Fessenden, Charles H. (1915).
Valve Gears. New York: McGraw Hill.
^ Wahl, Philipp (2013).
Piston spool valves and poppet valves.
Esslingen: Festo AG & Co. KG.
Torpedo Tube Manual
^ "A Handy Guide to Clinton Engines" (PDF). 1956. p. 2. Retrieved
October 2, 2015. R. P. M. 2200 - 3600
^ Thurston, R.H. (1878). A History of the Growth of the Steam Engine.
New York: Appleton & Co. p. 98.
^ Lardner, Dionysius (1840). The steam engine explained and
illustrated. London: Taylor and Walton. pp. 189–91.
^ Jacques Mouchly,
Valve Gear for Locomotives and Other
Engines, U.S. Patent 1,824,830, issued Sept. 29, 1931.
^ Herman G. Mueller, Steam Engine Valve, U.S. Patent 1,983,803, issued
Dec. 11, 1934.
^ 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.95
Reciprocating engines and configurations
& number of cylinders
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Junkers Jumo 222
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Savery Engine (1698)
Newcomen Memorial Engine
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Old Bess (1777)
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National Museum of Scotland engine (1786)
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Puffing Devil (1801)
London Steam Carriage (1803)
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"Pen-y-Darren" locomotive (1804)
Woolf's compound engine (1803)
Murray's Hypocycloidal Engine
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Glossary of steam locomotive components
History of steam road vehicles
Cugnot's fardier à vapeur (1769)
Murdoch's model steam carriage (1784)
Lean's Engine Reporter
List of steam technology patents
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