Why Pneumatic Vlaves ?

[hardhgear]

Hello everybody,
as we all nknow that all the engine are equiped with Pneumatic vlaves
So why they use Pneumatic instead of springs. Is it due to large RPM Or waht?

[hardhgear]

what the gas they use?
Is it pressure is constant or could be change ?

[AyrtonInmortal]

http://scarbsf1.com/valves.html

[jgredline]

Basically when you here the hydrolics went out its game over.
Valves usually end up inside pistons.

[zac510]

Hydraulics are different to pneumatics.

Scarbs' site sums it up quite well. At the time I think the coil spring limit was more like 13000. These days it is higher but penumatic valves have shown the way to over 20000 now.

[Tom]

I don't think springs are fast enough.

Pneumatics are the only thing that gets the valves up and down in time.

[manchild]

Pneumatics are the only thing that gets the valves up and down in time.

Only up, cams push the down

[Tom]

Of course, sorry

[jgredline]

Basically when you here the hydrolics went out its game over.
Valves usually end up inside pistons.

Yes your correct. I meant pneumatics.

[DaveKillens]

The more revs you ask of the engine, the stronger the spring has to be, so that it pushes the valve back up in time before the piston gets there and makes contact. For a steel (or any metal) wound spring, the further it compresses, it also resists. So if the first millimeter requires 500 Kg of force, it may require even more force too move it the next millimeter, and so on and so on. This requires a lot of force, making the cam and cam drive gear work much harder. And not only that, each compression and relaxation cycle generates a lot of heat. In NASCAR, where they have to run coil springs for the large valves they run almost red hot, they have to receive a constant bath of cooling oil or the valve spring would fail very quickly. And of course, the valve spring itself has mass, which resists the returning force., Inertia.
So the pneumatic system has a lot less mass, generates a lot less heat, does not ask the cam to push as hard to get equivalent valve lift, and returns the valve to the closed position much quicker than coil springs. All advantages in the racing world, but impractical in the real day to day world because if your valve system lost pressure overnight, when you tried to start your engine, all you would hear was all the valves making ugly contact with the pistons.

[m3_lover]

In the last twenty years in Nascar, the biggest technical improvement has been valve springs.

[jgredline]

The more revs you ask of the engine, the stronger the spring has to be, so that it pushes the valve back up in time before the piston gets there and makes contact. For a steel (or any metal) wound spring, the further it compresses, it also resists. So if the first millimeter requires 500 Kg of force, it may require even more force too move it the next millimeter, and so on and so on. This requires a lot of force, making the cam and cam drive gear work much harder. And not only that, each compression and relaxation cycle generates a lot of heat. In NASCAR, where they have to run coil springs for the large valves they run almost red hot, they have to receive a constant bath of cooling oil or the valve spring would fail very quickly. And of course, the valve spring itself has mass, which resists the returning force., Inertia.
So the pneumatic system has a lot less mass, generates a lot less heat, does not ask the cam to push as hard to get equivalent valve lift, and returns the valve to the closed position much quicker than coil springs. All advantages in the racing world, but impractical in the real day to day world because if your valve system lost pressure overnight, when you tried to start your engine, all you would hear was all the valves making ugly contact with the pistons.

Dave
Very well explained.
Thanks

[hardhgear]

Thank you DaveKillens So much
But iwould like to know if the the gas type (Is it air or other gas). is it works under constatnt pressure or they change the pressure as a part of the engine setup which change to meet the race requirements.

[DaveKillens]

I believe all the valve pneumatics are plumbed to a common reservoir, kept at a specific pressure. I also believe they have another pressurized bottle and valves to add pressure to the first reservoir if pressure drops. I do know that if there is more loss, they can quickly repressurize the system during a pit stop. Of course, that's for a slow leak. If the leakage is too much, the system eventually can't close the valves quick enough, and the valves strike the piston, end of story. I believe that the system pressure is one parameter monitored by telemetry, so engineers can avoid total, catastrophic destruction of the engine.

[hardhgear]

This web page contain information about the pneumatic valaves gas
http://www.indiacar.com/index2.asp?page ... engine.htm