Poppet valve

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.

[8] Poppet valves are best known for their use in internal combustion and steam engines, but are used in general pneumatic and hydraulic circuits where a pulsed flow control is wanted.

The Presta valve has no spring and relies on a pressure differential for opening and closing while being inflated.

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.

[9] 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".

In a typical modern mass-production engines, the valves are solid and made from steel alloys.

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, such as when the throttle is abruptly closed.

Secondly, lead additives had been used in petrol (gasoline) since the 1920s, to prevent engine knocking and provide lubrication for the valves.

[10] 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.

[11] 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[12] 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.

James Watt was using poppet valves to control the flow of steam into the cylinders of his beam engines in the 1770s.

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.