Brian builds a Corliss

[aostling]

. . . I'm not really sure what's going on here . . .

Are we waiting for adjustable links?

[brian Rupnow]

No, not adjustable links. I have done something wrong, and I'm trying to figure out what it was. I can get the piston to retract like a gunshot but the piston extends in a very wimpy manner. I'm making one new rotary valve right now, as I had one where the end that was supposed to be 0.125 was actually 0.121 and the adjustable link wouldn't lock on it very well.

[aostling]

. . . I can get the piston to retract like a gunshot but the piston extends in a very wimpy manner. . . .

On a Corliss steam engine the rotary valves are open for only a small portion of a rotation. This is so that the brief puff of high pressure stream admitted directly into the cylinder can then expand while its pressure drops, so that exhaust steam will have minimum residual energy.

If you are using relatively low air pressure, this expansion could result in the cylinder gauge pressure going negative before the end of the stroke. You can test this theory by increasing your air pressure in an attempt to emulate the steam engine.

[J Tiers]

On a Corliss steam engine the rotary valves are open for only a small portion of a rotation. This is so that the high pressure stream admitted directly into the cylinder can then expand while its pressure drops, so that exhaust steam will not have minimum residual energy.

............................................

Accounting for the releasing valve gear and the "dashpots". But I think a good bit of that was a later enhancement, and not necessarily original.

[RB211]

Does steam expand more than air? Are we dealing with an issue stemming from the fact that physics do not scale down?

[aostling]

. . . Are we dealing with an issue stemming from the fact that physics do not scale down?

The issue is that we don't know if Brian has used air pressure equal to what the steam pressure would be in a Corliss steam engine.

[brian Rupnow]

Compressed air does not expand nearly as much as steam. A lot of the energy from steam is involved with a change of state from a gas to a liquid. I made the video using compressed air at a high pressure. I'm pretty certain that I was only getting power on the retraction stroke, and the flywheel was just "carrying" things thru the extension stroke.

[J Tiers]

Unlike steam, compressed air does not further expand. A lot of the energy from steam is involved with a change of state from a gas to a liquid. I made the video using compressed air at a high pressure. I'm pretty certain that I was only getting power on the retraction stroke, and the flywheel was just "carrying" things thru the extension stroke.

Not sure about your video, but compressed air certainly "expands further". Steam is "better at doing that", but both do it

Steam (and compressed air) if "cut off" (admission stopped) at some portion of the stroke, such as 1/3, will expand, dropping in pressure and temperature as it does so. Steam usually starts hotter, and has more energy content per deg C, but both will act in generally the same way. Steam is a gas, and while not a "perfect" gas (air is much more so), generally follows the gas laws the same as any other gas, with some differences. It cools as it expands, etc, like any gas.

The differences with air vs saturated steam include that air is "superheated", meaning that it is well above it's temperature of condensation at usual temperatures, that steam holds somewhat more energy than air, and that steam is usually hotter than compressed air at the point of use. Being hotter, it has more energy than compressed air at ambient temps, and steam (water) has more energy content at a given temp than air, so hot steam has significantly more energy than cold compressed air.

Specifics are best found by consulting tables of the properties of steam, and comparing them to properties of a "perfect gas", which air is closer to.

Saturated steam is just barely above its condensation temp when generated at low pressure, and should rapidly fall below as it expands. Often, precautions are taken to ensure that the steam does not condense in the cylinder (steam jacketing, for instance).

So, steam is "more effective" than compressed air, but both will expand and act in broadly similar ways. Steam just does things better than air, due to the specific heat of steam being higher vs air. Steam is not "completely different", it is "somewhat different".

Check this link: https://www.quora.com/Can-saturated-...s-an-ideal-gas

It suggests that at the typical pressures involved with model steam engines, steam is quite close to an ideal gas, and will act pretty close to how air acts at the same temperature and pressure.

[brian Rupnow]

Jerry--you're right. I modified my post.---Brian

[sid pileski]

There must be something fundamentally wrong here.
There are many other builds of this engine running on very low pressures. (10>).
Yes, steam is a different animal, but it’s not the silver bullet here by any means.
Go back to the basics of construction, timing, etc.

[PStechPaul]

It should be possible to set the engine manually to various positions and then apply compressed air to see if the piston moves as expected. It should not stall during the time the intake valve is open, and the exhaust is closed. It may be helpful to make a valve timing diagram showing the condition of the valves at each angular position of the crank. At least the effect should be the same for the two power strokes.

These might help:

http://wkinsler.com/technology/corliss/index.html

https://www.modelengineeringwebsite.com/Corliss_mill_engine.html

http://www.patbelford.com/toys/library/reynolds-engine/index.html

An example of a valve timing diagram:

https://yanswerz.blogspot.com/2009/12/valve-timing-diagram-of-four-stroke.html

I haven't really examined these, but they should give some ideas.

[aostling]

It's a great day in Barrie!!! My Corliss engine ran today for it's very first time. I have a lot of adjustments and tweaks to do before this engine is running as good as some I have seen on the internet, but it makes my heart sing to see the engine setting there huffing away.
https://www.youtube.com/watch?v=NCl0flMy2iA

That first run nine days ago looks pretty good. Has the smoothness actually gotten worse?

[brian Rupnow]

On that first run, I was only getting power on the retract stroke of the piston, non on the extend stroke. The flywheel is big enough to carry it thru and look like it is running better than it actually is. I've been down with some kind of flue this week, and have ordered a bit of tooling that I require to correct whatever is not right. My new tooling (mainly taps and tap drills) should be here this week, and hopefully I will get things sorted. I simply haven't felt like doing much in my shop this week. Setting around reading and growing bored.

[Jon Heron]

On that first run, I was only getting power on the retract stroke of the piston, non on the extend stroke. The flywheel is big enough to carry it thru and look like it is running better than it actually is. I've been down with some kind of flue this week, and have ordered a bit of tooling that I require to correct whatever is not right. My new tooling (mainly taps and tap drills) should be here this week, and hopefully I will get things sorted. I simply haven't felt like doing much in my shop this week. Setting around reading and growing bored.

Feel better Brian! The wuhan flu has been spreading like wild fire around us lately, I had three customers and my mother in law all come down with it just in the last 2 days... Last week 3 colleagues and more customers...
Chicken soup and lots of rest for the win!
All the best,
Jon

[Jim Stewart]

Feel better Brian! The wuhan flu has been spreading like wild fire around us lately, I had three customers and my mother in law all come down with it just in the last 2 days... Last week 3 colleagues and more customers...
Chicken soup and lots of rest for the win!
All the best,
Jon

Wuhan flu! Jeezus H. Christ. It's COVID-19.

-js