Steam engine on compressed air

[Gordon]

I am trying to run a Corliss engine on compressed air using an airbrush compressor. My question is what am I missing in my calculations? The engine has 1.125 bore x 1.5 stroke. This calculates to 1.49 ci/stroke. Since it is powered both directions it should use 2.9 ci per revolution of the flywheel. The compressor is rated for 1 cubic feet per minute with 40 psi to 58 psi set points. 1 cf = 1728 ci. 1728/2.9 should result in 595 revolutions. It is turning the flywheel at probably 25 RPM and it shows no pressure on the gage. It runs on my shop compressor with at about 5-7 PSI. I realize that there are probably some leakage around the piston and the valves but this is far from the expected result. Other folks are running similar engines on airbrush compressors. Is there a problem with my calculations or is the compressor just not putting out the volume that is is rated for?

 

[Steamchick]

Sounds like the compressor is leaking at the internal valves, so simply not pumping a lot...
I have had that with my 'Fridge compressor used for driving models. I also have a pump for removing engine oil from sumps, and that needs priming with oil otherwise it can't lift the oil out of the sump! - Once oil (sealed) it works fine.
So maybe try squirting a little oil into the air intake of your compressor, to see if that is leaking-back? If a drop of oil causes it to pump much better, then strip-it, clean the non-return valves, check piston for wear, repair, rebuild and try again?
As the compressor is meant for spraying paint, you'll need to clean it of oil before painting anything! - if it can pump enough air to do the painting...
K2

 

[Steamchick]

Or maybe the Corlis engine valves and piston are just leaking enough that they need much more volume delivering? The 595rpm is a calculated perfect system, not real, not taking into account any adiabatic or isothermal phases of the engine (valve-cut-off, etc.). So a squirt of oil into the air intake of the engine may help a bit?
It does sound like the engine simply needs MORE AIR supplied, which in turn will develop a measurable back pressure.
I once tried to calibrate air consumption unsuccessfully on an engine. I had a 2l pop-bottle, fitted a connection into the plastic screw top, filled it with air to a set pressure, closed-off the compressor supply, then tried to figure out how many strokes/revolutions of the engine it could run.
Completely useless experiment as it was too crude. But it suggested the engine efficiency was but a few %! Maybe you have 25/595 = 4% efficiency? - Not unreal? - I don't know.
K2

 

[Jasonb]

I expect the 1cfm rating for the compressor is actually it's displacement as that is how a lot of small compressors are described due to it sounding better in the sales blurb. What you really want is the FAD "Free Air Delivery" which is the volume of air it will actually put out. and this can be 40 to 50% of the displacement.

Your engine is drawing air at a higher rate than would flow through the small outlet of an airbrush so you are also not building any pressure, think of it like when you first turn on a large shop compressor with a tank, the needle takes a while to rise if you are not drawing air, if the outlet is fully open then the needle won't move.

 

[Richard Hed]

I am trying to run a Corliss engine on compressed air using an airbrush compressor. My question is what am I missing in my calculations? The engine has 1.125 bore x 1.5 stroke. This calculates to 1.49 ci/stroke. Since it is powered both directions it should use 2.9 ci per revolution of the flywheel. The compressor is rated for 1 cubic feet per minute with 40 psi to 58 psi set points. 1 cf = 1728 ci. 1728/2.9 should result in 595 revolutions. It is turning the flywheel at probably 25 RPM and it shows no pressure on the gage. It runs on my shop compressor with at about 5-7 PSI. I realize that there are probably some leakage around the piston and the valves but this is far from the expected result. Other folks are running similar engines on airbrush compressors. Is there a problem with my calculations or is the compressor just not putting out the volume that is is rated for?

I didn't know you had a Corliss! What kind? Can we see it?

 

[The Ignoble Troll]

I expect the 1cfm rating for the compressor is actually it's displacement as that is how a lot of small compressors are described due to it sounding better in the sales blurb. What you really want is the FAD "Free Air Delivery" which is the volume of air it will actually put out. and this can be 40 to 50% of the displacement.

Your engine is drawing air at a higher rate than would flow through the small outlet of an airbrush so you are also not building any pressure, think of it like when you first turn on a large shop compressor with a tank, the needle takes a while to rise if you are not drawing air, if the outlet is fully open then the needle won't move.

This^

It's the difference between SCFM, ACFM, and ICFM.


This might help

https://www.thecompressedairblog.co...most popular,flow rate at standard conditions.