Model Engine Maker
Help! => Specific Engine Help => Topic started by: JR72 on October 31, 2019, 05:27:28 PM
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I want to use graphited packing as a piston ring, the piston is 1 inch dia. ( similar to the Victoria ) the plans show a groove of 3/32" deep by 1/8" wide. It seems the most popular size of the packing is 1/16". Would this mean the packing is wound round two or three times given that it would compress? Would it be better to form a smaller grove? I would prefer to use graphited packing and not piston rings as I doubt if I will run the engine very much but would like to keep the cylinder bore lubricated.
Your help will be much appreciated.
Thanks
John
(JR72)
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Make the groove the size on the plans (you can then fit piston rings in the future if you choose) and wind the yarn round the piston a good few times.
I normally separate out the strands in the yarn to make it thinner: you get more rotations and it is easier to adjust the amount of packing for a good fit ;)
Jo
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Many thanks Jo for your quick reply. Your advise seems good to me I will certainly give it a try thank you.
John
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Bit of 1/8" dia with an angled cut to the ends would pack down perfectly into that size groove as cross section of groove is just a fraction less than cross section of 1/8" dia.
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Many thanks Jason, I now have two options using the same size groove so I will see how I get on.
It`s replies like this that makes this Forum a great place to be.
Thanks again
John
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John....
Remember the graphited yarn in this application will be a pressure energized ring....so yes by all means, machine the piston 'ring' groove as per Drawing dimensions and then as suggested unravel the yarn to add additional windings whilst still maintaining a vertical float for the yarn
The impregnated graphite provides excellent lubricity between the piston OD & the cylinder bore, and eliminates any potential for the natural twine/cotton/yarn to stick or burn at our modest steam pressure/temperatures and whilst at all times providing a ZERO steam bypass in your engine :ThumbsUp:
People tend to dismiss 100 year old :happyreader: technology just to use the latest & greatest ...[sometimes we must ask at what cost?]
[As a 1st year Apprentice :old: 55+ years ago, I remember my Saturday overtime shift unravelling graphited yarn from those large Silver Boxes of J Walker Gaphited Packings, then repacking the gland seal of a 48" diameter [very scored] vertical piston rod in an oil/water extrusion press imported from the UK in 1948?......the actual gland seal was ten [10] split cut bands of 1" square JW Grade 600...[the 600 was a steam temperature rating in degrees F} and nothing to do with the oil/water fluid at 500 PSI working pressure @ ambient temperature]
So as that Apprentice, I asked my Tradesman why I could not make one semi continious ring of x 10 high instead of the 10 x individual staggered rings?......:facepalm: & :hammerbash:... I then learnt a little of what amounts to fluid sealing characteristics as lectured by a Mr Daniel Bernouli ...which is part of the basis of thermo dynamics and still valid today some 300 years later
Derek
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Thank you Derek,
I am so pleased with the response I have received from yourself, Jo and Jason. Really good to know that I have made the right choice especially with a long tried and tested method. I have already ordered the graphited packing and look forward to having a go.
Tanks again to all of you.
John
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Hi John, I make my own graphite yarn by running thin cotton string over the carpenters pencil lead.... works for me ok impregnated with thin oil .
Willy
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Hi Willy,
Many thanks for the tip, I might try that but as I have order he graphite string (only £2.50 inc. p&p ) I can try both. But that is a handy tip for the future.
Thanks again
John