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Mark V
| Joined: 25 Aug 2005 |
| Posts: 500 |
| Location: East Coast |
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 Posted: Tue Jul 27, 2010 12:28 pm |
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| Ditch wrote: |
That all looks very funky & expensive..
Had a reed valve on my 210 years ago, know they make it quicker but would love to know why, or what they actually do..?? |
Reed valves are commonly used in high-performance versions of the two-stroke engine, where they control the fuel-air mixture admitted to the crankcase. As the piston rises in the cylinder a vacuum is created in the crankcase beneath the piston. This vacuum opens the valve and admits the fuel-air mixture into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber.[1]
Composite materials are preferred in racing engines, especially go karts, because the stiffness of the petals can be easily tuned and they are relatively safe in failure. High-speed impact takes its toll on all reed valves, with metal valves suffering in fatigue. The physical inertia of reed valves means that they are not as entirely precise in action as rotary valves, a rotary valve engine may run better than a reed valve engine at a small rpm range but the reed valve engine often runs better over a wider rpm range. More sophisticated designs partly address this by creating multi-stage reeds with smaller, more responsive reeds within larger ones that provide more volume later in the cycle. Nevertheless, current technology favors reed valves almost to the exclusion of rotary valves due to their simplicity and low implementation costs. |
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Ditch
| Joined: 20 Jul 2010 |
| Posts: 135 |
| Location: Sunny Suffolk |
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| Posted: Tue Jul 27, 2010 2:42 pm |
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| Mark V wrote: | Reed valves are commonly used in high-performance versions of the two-stroke engine, where they control the fuel-air mixture admitted to the crankcase. As the piston rises in the cylinder a vacuum is created in the crankcase beneath the piston. This vacuum opens the valve and admits the fuel-air mixture into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber.[1]
Composite materials are preferred in racing engines, especially go karts, because the stiffness of the petals can be easily tuned and they are relatively safe in failure. High-speed impact takes its toll on all reed valves, with metal valves suffering in fatigue. The physical inertia of reed valves means that they are not as entirely precise in action as rotary valves, a rotary valve engine may run better than a reed valve engine at a small rpm range but the reed valve engine often runs better over a wider rpm range. More sophisticated designs partly address this by creating multi-stage reeds with smaller, more responsive reeds within larger ones that provide more volume later in the cycle. Nevertheless, current technology favors reed valves almost to the exclusion of rotary valves due to their simplicity and low implementation costs. |
Ahhh basicaly it closes the inlet port to maintain the pressure inside the cylinder/combustion chamber..
I thought it created a vaccum to suck in more air/fuel mixture..
That makes more sense, cheers for that..  |
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