Relaxing Rings

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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DetroiTug
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Re: Relaxing Rings

Post by DetroiTug » Thu Jul 19, 2018 7:43 pm

Fair enough, but keep in mind, a 2.5" piston is around 5 square inches of surface area on the face. Even at 10 psi of steam, that is 50 pounds of force moving the piston back and forth. The steam has no trouble moving the piston, especially hot and with some lubrication.

I was just wondering, I had never heard of purposely removing the tension of piston rings. On the car side of things we have to watch the amount of superheat to avoid damaging the rings (overheating and losing their tension). Because when that happens, the steam goes right past the piston and no work out of it - it's lost.

-Ron
Mike Rometer
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Re: Relaxing Rings

Post by Mike Rometer » Thu Jul 16, 2020 3:22 pm

Ok! So I suppose someone has to do something productive (instead of winding up the forum populace :lol: ) I've resurrected this thread to show the finale. These ring rightly belong with my twin.

Looking at the rings I have in stock I realised that the reason they were excessively tight was because they are not STD rings but 'oversize'! I tried to determine by how much, without conclusive result. Knowing how I acquired them they could easily be 'various', there were no clues on them, and no packets!

I took a suitable disc and carved a hole in it, bore size plus 0.010" i.e. 2.510", even at that there was some overlap so they could be +0.020" or even +0.030".
Piston Rings (2) (600 x 450).jpg
Piston Rings (2) (600 x 450).jpg (55.2 KiB) Viewed 351 times


I then thinned it down to what I guessed was near enough the same weight as four rings, and leaving it long enough for same, as I'd reckoned I'd probably get a more standard result in bulk. My idea for the small weight was that I wanted to allow as normal a cooling as possible whilst maintaining enough rigidity. All pure speculation and supposition, as I think we agreed further back that this was a "suck it and see" job.
Piston Rings (3) (600 x 450).jpg
Piston Rings (3) (600 x 450).jpg (66.53 KiB) Viewed 351 times
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Mike Rometer
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Re: Relaxing Rings

Post by Mike Rometer » Thu Jul 16, 2020 3:34 pm

The ring stack was then placed on a fire-brick, and with the gas blow-lamp pointing straight down in the centre, heated as evenly as possible to a dull glow. Here I have to say that the camera seems to be lying, as it never looked that red to the naked eye.
Piston Rings (5) (600 x 450).jpg
Piston Rings (5) (600 x 450).jpg (63.97 KiB) Viewed 350 times
I allowed them to cool on the fire-brrick whilst I had a natter with a neighbour (15-20 mins?). On removal from the ring they opened very little, so I would suggest if doing this again, add at least another 0.010" to the bore as these are to my 'feel', just a touch on the slack side, though that may be Ok with steam. No matter because I can always set the gap and then treat them as new home made rings with a re-heat.
Piston Rings (6) (600 x 450).jpg
Piston Rings (6) (600 x 450).jpg (61.21 KiB) Viewed 350 times
This last pic shows them with a new one alongside.

The rings seem to still be perfectly circular as I can see no light round them in the final bore. I do still have a few more so I could go round again with the bigger size dummy, if I feel inclined.
Retirement is about doing what floats your boat!

A BODGE : - A Bit Of Damn Good Engineering.
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