Cylinder temperatures

[tecnamflyer]

Team,
Has anyone got any idea of the actual temperature a set of bronze cylinders and pistons with a superheated boiler would reach in normal club track running. 1.625" bore cylinders
Thanks,
Paul

[jma1009]

when jim ewins did his research the minimum cylinder temperature he got was 121 degrees celcius. that was with radiant superheaters. he got higher temperatures when the loco was being worked hard.
the loco he was testing had inside cylinders.
hope that helps.

[tecnamflyer]

I am considering using Parker PTFE.Fibreglass rings but Parker are telling me that they do not like going over 200C, hence my posting.
I cannot attach the parker file as it is too big.
Paul

Attachments:

[donashton]

The temperature will vary a surprising amount depending upon the working (as Julian says) and upon where it is measured. Do you want the temperature of the steam at inlet, or exhaust, or the valve liner wall or main bore wall temperatures? It's difficult to get precise figures anyway. If you consider the rings not to be in contact with the steam, a reasonable assumption, reaching 200C would appear unlikely.

Don

[baggo]

I did try measuring the cylinder temperature of my Helen Long when on a rolling road but the digital thermometer I used only went to 150°C and the temperature was higher than that
The steam is very hot and rapidly destroyed silicon O rings on the manifold joints as well as turning the brass manifold blue! However. the pistons are fitted with PTFE rings and the piston valves have PTFE heads and they've survived for 4 years now and are still steam tight.

John

[durhambuilder]

You could try temperature indicator strips,

www.thelabwarehouse.com/varius.engine?w=2&ref=16&language=1&pref=2&group=3&code=A083003

Some have a 'one way' colour change so having stopped at the end of a run will stay showing the maximum temperatures reached.

[jma1009]

Paul,
are you referring to piston rings or piston valve rings?
im afraid ive never built a loco with piston valves, and all my locos have the old fashioned asbestos graphite packing.
i would have thought you would be ok with parker rings. the only problems i have seen have been with people making piston valves out of stainless and jamming up solid! i would never use 'O' rings for piston rings (try using a pencil rubber on a cylinder bore and see what happens!). there is a school of thought that hard drawn phosphor bronze is quite good as piston rings in gunmetal cylinders, though personally i use cast bronze pistons in gunmetal cylinders with asbestos graphite packing. i dont think it's mechanically sensible to have the piston rings of a harder material than the cylinders. i use the old fashioned method partly because ive got plenty of it, and partly coz i was taught how to pack them properly when a nipper, and my use of hydrostatic lubricators allows me to be sure cylinder oil is being fed. when ive used up all my asbestos graphite packing i might have a try at the more modern methods!
john's excellent construction series of HELEN LONG on his website can be recommended for PTFE in all sorts of applications including pistons. (i do use it sometimes in other circumstances!)
i might add that none of my locos have radiant superheaters, just the LBSC type spearhead elements, and i make them in such proportions to the superheater flue that they can be easily cleaned with a fluebrush, so ensuring maximum efficiency (which i have always thought a bit doubtful with the coaxial type)
cheers,
julian

[steamlaser]

When I have need to measure temperatures deep inside metal structures, very fine thermocouples were used.
We drilled tiny holes deep into the material and inserted very fine thermocouple wires. We put a tiny amount of copper/ silcone oil in the bottom of the holes to give good thermal contact.For your purposes a "cold Junction" is not required.
By the way our pressures went up to over 12 MBars and when things went bang it was exciting!

[pault]

Hi Paul
It is in fact a difficult thing to measure or even have a sensible guess at what temperatures the rings will see. As the cylinders are a heat engine the whole thing revolves around heat transfer, and so as a result the temperatures are fluctuating at most locations, and there are temperature gradients all over the block. Throw in the variations in superheat and pressures within the cylinder, and it all becomes very dynamic.

Personally I have never used PTFE rings but I have used it for piston glands and various seals without a problem from the experiences of people on this forum it looks like you won’t have a problem.

Regards
Paul