Vertical twin steam engine

[AStroudParticipant @astroud]

Happy Christmas all

Here’s my twin cylinder engine, 1″ bore and stroke twin cylinder, single acting with spool valves. It is nearly complete, just needs supply and exhaust plumbing however I could not resist rigging up some piping to see if it would run.

It would not despite the usual messing about with the timing and I think there are 2 reasons which combine together. First I thought I would be clever and remove the need for valve springs by porting the air in at the top of the valve chamber so pushing the spools down on the eccentrics all the time. It works but I think the force is too strong and resists motion especially when I turn up the air pressure in an attempt to get it running. This combined with a 90 degree crank (just to be different) means the flywheel inertia is not enough to turn it over until the next power stroke. I put a small chuck on the other crankshaft end for more inertia but still no go however I do feel power pulses.

I knew I was risking this when I drew up the design so I am not too disheartened and will now make a 180 degree crankshaft and hopefully with low air pressure it will run. If  still a failure I will need to make new valves and use valve springs.

Andrew

[JasonBModerator @jasonb]

Yes probably a bit too long between power strokes being single acting with the 90deg crank, would be Ok if they were double acting.

[cedric 1Participant @cedric]

A single cylinder single acting has a longer gap between power strokes and works just fine. So I suspect your problem is more in the valve gear.

[JasonBModerator @jasonb]

With pistons of 1″ diameter and say valves of 1/4″ diameter there will always be a lot more area for pressure to  act against on the piston than the valve. Basic lbs per Sq inch

If a 180deg crank is fitted then there will be power to one piston almost all the time so you have 8 times as much force on one piston than the two valves added together so the engine should be able to overcome any valve issues.

With the 90degree crank you are only getting power for 3/4 of each revolution at the most. The remaining 1/4 of the revolution when neither piston is on a power stroke will get the full force of the air against the spool valves and that is likely what is stalling the engine. Even if the valves are redesigned to use springs the engine has to be able to compress those springs when there is no power from the pistons.

 

If you look at the popular twin cylinder single acting engines like the Stuart Sirrus, Star, Sun, MTBs etc they all run 180 deg crankshafts. As there is always power to one piston to push the spent air/steam out of the other cylinder which also helps

[AStroudParticipant @astroud]

Thanks.

The engine tries to run as I can feel the downward pulses and having played with the valve timing I feel it is the crankshaft which is the problem. A 90 degree crank is a bit daft with hindsight but I wanted to try something different. I will give an update once the new crank has been built and installed.

[AStroudParticipant @astroud]

I have made and installed a 180 degree crankshaft and after a fair bit of fettling the engine now runs nicely.

The air spring valves work well and it will run at 2-5psi and is still bedding in. I have also made a larger flywheel which has helped with the smooth running. After I have made a slot in the base so the flywheel will fit and made some supply piping I will post a video.

Andrew 

[AStroudParticipant @astroud]

I have finished off the piping and the base, here is a short clip of the engine running

https://youtu.be/QejAS9MsrpI

[Michael GilliganParticipant @michaelgilligan61133]

Nicely done

MichaelG.

[Harry WilkesParticipant @harrywilkes58467]

Nice one

H

[Author]

Posts