Atmospheric Intake Valve on "Modern Engines"

[BronxFigs]

I have a question....well, some questions.

Can an atmospheric intake work on modern design, model gas engines? For example....take the "Hoglett" V-Twin....can atmospheric intake work on this kind of 4 stroke engine, with a cam controlled exhaust valve?

Is this type of valving used only on the old fashioned Hit and miss engines with a governor, and latching mechanism for exhaust valve control?

My best guess would be "no" or it would be a regular feature in most of the designs we build. However, does this type of valve have a useful function, or can it be adapted to work in our exhibition-type, model engines?


Frank

 

[///]

My best guess would be "no" or it would be a regular feature in most of the designs we build.

My guess would be "yes".
I believe the reason they aren't used is because a cam operated valve allows control of the valves timing, like duration and overlap etc etc.

 

[Brian Rupnow]

Atmospheric intake valves don't close rapidly enough to work on a high revving engine. They need to have a very light valve spring, to open under atmospheric pressure. The fact that they require such a light spring prevents them from closing fast. When driven open with a cam, you can use a much stronger spring, and the valve will consequently close much faster. Otherwise your engine will "float the valves" with consequent misfiring, backfiring, and the chance that the piston will reach top dead center before the valve has fully closed, which bends the valve stem and can destroy the piston.

 

[Jasonb]

I don't think the valve could keep pace as the revs get higher, cam opperated allows a stiffer spring so the valve will shut faster and can be opened earlier as the vacuum in the cylinder starts to rise.

J

Brian beat me to it

 

[BronxFigs]

The above answers seem to indicate that these valves had their application, and their limits with the low-revving "antique" type engines.

I'm glad I asked....and thanks for the answers.


Frank

 

[trev1]

Another side issue is that the cam operated valve allows more air fuel mix into the cylinder due to the fact that the atmospheric intake design, the cylinder vacuum has to get to a point where the vacuum has to overcome the spring pressure before thevalve opens, meaning there is a lot of piston travel back down the cylinder before intake actually starts. A cam operated intake valve is usually open just after top dead center , this gives more air fuel mix into the cylinder and more power.

 

[Swifty]

Isn't a reed valve on two stroke engines an atmospheric valve? These seem to work alright.

Paul.

 

[Lew Hartswick]

And for the truly performance addicted there is Desmodromic valves.
..Lew...

 

[Brian Rupnow]

Isn't a reed valve on two stroke engines an atmospheric valve? These seem to work alright.

Paul.

A reed valve only has to move a few thousandths of an inch, and has much less mass, as the head, stem, spring and spring retainer are all incorporated into one piece of flat spring steel. Having less mass means that it can react much faster, and they are not depending only on atmospheric pressure to operate them. The crankcases of 2 stroke engines are pressurized.

 

[Rustkolector]

I have a 3/4 hp 1925 Briggs and Stratton model FH throttle governed engine that uses an atmospheric intake valve. It was designed to operate at 1200-1800 RPM. It will, however, run much faster and develop power. It obviously is not the right intake valve mechanism for high output high speed operation for the reasons previously stated. It does work surprisingly well however. I also built one of Jerry Howell's "Bill" model engines using the same type intake valve. It will run merrily along all day at 1600 RPM, and will run much faster if I let it. Atmospheric intake valves should work well on the Hoglet engine and also Randall's Open Six engine since they are both low/medium speed engines.

Jeff

 

[Hopper]

Harley-Davidson ran atmospheric intake valves on some of their engines up to about 1910 or so. So it can be done. But as discussed already, good for low revs only and reduces the power ouput compared with cam operated.
So if you want a model engine to just putter along at low rpm, it would work.

 

[johnlaudano]

the comments above are accurate about the limitations of atmospheric intake valves but for low speed low powered models they do work. see the video of my homemade v-twin with atmospheric intake valves. its based on Jerry Howells "Bill" single cylinder engine. mine in the video is running on propane. [ame]http://www.youtube.com/watch?v=KFRBsLZa5sE[/ame]
my next project uses cam-operated valves in order to eliminate the headache of trying to get the valve spring size correct.
John

 

[BronxFigs]

Love the "Bill" as a V-Twin . Very inventive design.

Frank