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Difference between revisions of "Poppet valve"
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[[Image:4-Stroke-Engine.gif|thumb|right|Poppet valves in action at the top of the cylinder]] | [[Image:4-Stroke-Engine.gif|thumb|right|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 | 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. Marotta direct acting solenoid valves use a balanced poppet to keep solenoid coil size and power requirements to a minimum. <ref name="balanced_poppet_design_reference">"[http://www.marotta.com/tech-info-a-faqs/balanced-poppet.html What is a Balanced Poppet? on Marotta.com]."</ref> | ||
==Applications== | ==Applications== | ||
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==Internal combustion engine== | ==Internal combustion engine== | ||
[[Image:Four stroke engine diagram.jpg|thumbnail|right|175px|Components of a typical, [[four stroke cycle]], DOHC piston engine:<br>(E) Exhaust [[camshaft]],<br>(I) Intake camshaft,<br>(S) [[Spark plug]],<br>(V) Valves,<br>(P) [[Piston]],<br>(R) [[Connecting rod]],<br>(C) [[Crankshaft]],<br>(W) Water jacket for coolant flow.]] | [[Image:Four stroke engine diagram.jpg|thumbnail|right|175px|Components of a typical, [[four stroke cycle]], DOHC piston engine:<br>(E) Exhaust [[camshaft]],<br>(I) Intake camshaft,<br>(S) [[Spark plug]],<br>(V) Valves,<br>(P) [[Piston]],<br>(R) [[Connecting rod]],<br>(C) [[Crankshaft]],<br>(W) [[Water jacket]] for coolant flow.]] | ||
''Poppet valves'' are used in most [[piston engine]]s to open and close the intake and exhaust [[cylinder head porting|ports]] in the [[cylinder head]]. The valve is usually a flat disk of metal with a long rod known as the ''valve stem'' out one end. The stem is used to push down on the valve and open it, with a spring generally used to close it when the stem is not being pushed on. [[Desmodromic valve]]s are closed by positive mechanical action instead of by a spring, and are used in some high speed [[motorcycle]] and auto racing engines, eliminating '[[valve float]]' at high [[RPM]]. | ''Poppet valves'' are used in most [[piston engine]]s to open and close the intake and exhaust [[cylinder head porting|ports]] in the [[cylinder head]]. The valve is usually a flat disk of metal with a long rod known as the ''valve stem'' out one end. The stem is used to push down on the valve and open it, with a spring generally used to close it when the stem is not being pushed on. [[Desmodromic valve]]s are closed by positive mechanical action instead of by a spring, and are used in some high speed [[motorcycle]] and auto racing engines, eliminating '[[valve float]]' at high [[RPM]]. | ||
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Although better heat conductors, aluminum cylinder heads require steel [[valve seat]] inserts while cast iron cylinder heads often used integral valve seats in the past. | Although better heat conductors, aluminum cylinder heads require steel [[valve seat]] inserts while cast iron cylinder heads often used 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]]. A rubber lip-type seal ensures that excessive amounts of oil are 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 seals are characterized by a puff of blue smoke from the exhaust when pressing back down on the accelerator pedal after allowing the engine to over-run, such as when changing gears. | 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]]. A rubber lip-type seal ensures that excessive amounts of oil are 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 seals are characterized by a puff of blue smoke from the exhaust when pressing back down on the accelerator pedal after allowing the engine to over-run, such as when changing gears. | ||
===Valve position=== | ===Valve position=== | ||