Silicone piston rings

Discussion in 'General Engine Discussion' started by kiwi2, Dec 13, 2018.

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  1. Dec 13, 2018 #1

    kiwi2

    kiwi2

    kiwi2

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    Hi,
    I'm going to have a go at a marine engine for my next project.
    http://www.john-tom.com/MyPlans/Steam Engines/MarineEngine.pdf
    In the past I have made the pistons from phosphor bronze with a couple of fine grooves cut into them to retain oil.
    I was watching Keith Appleton on Youtube () and he used silicone piston rings to repair an old engine. I would like to use the same system for the marine engine but I'm not sure how to implement it.
    The plans call for a 1" piston but I think I'll probably go for 3/4".
    Are silicone piston rings just ordinary silicone O rings with the standard clearances normally associated with O rings?
    If so, what wall thickness would be appropriate for a 3/4" bore? On the Keith Appleton video it looks to be about 1/8".
    Regards,
    Alan C.
     
  2. Dec 13, 2018 #2

    Jasonb

    Jasonb

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    For model work you want less "squash" of the ring than you will find in most published tables, something like Model Engineers handbook or a printed version of the Reeves catalogue give the groove sizes that will work for us.

    Yes the Silicon rings are basically the same as a bog standard black one but from Silicon, Vitron will also work. For that sort of bore I would go with nominal 3/32" section imperial ring or 2.4mm metric
     
  3. Dec 15, 2018 #3

    kiwi2

    kiwi2

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    Thanks Jason.
     
  4. Dec 15, 2018 #4

    fcheslop

    fcheslop

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    This companies sizing works well although I tend to go a thou or so deeper
    http://www.glrkennions.co.uk/
    The O ring code for a 3/4 bore would be 113 the groove would be 0.141 wide and 0.091 deep
    As does Blackgates
     
    Last edited: Dec 15, 2018
  5. Dec 16, 2018 #5

    kiwi2

    kiwi2

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    Thanks fcheslop. Very useful information.
     
  6. Dec 16, 2018 #6

    Blogwitch

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    Be very careful when using silicon in an engine. Viton is perfect for rings but silicon is very susceptible to different liquids, plus it is very soft when compared to butyl or viton, maybe causing too much friction.
    WD40 (used for cleaning) makes it swell up and disintegrate, causing a gooey mess, other liquids may have other bad habits when in contact with it.

    John
     
  7. Dec 16, 2018 #7

    kitson

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    A much better option are Quad or X rings they have four points of contact and can be obtained in a wide range of sizes imperial and that strange system shudder metric also various materials as with "O" rings i have run my steam engine with 1" bores for 8 years with no problems i purchased 10 and have only used 2
     
  8. Dec 17, 2018 #8

    kiwi2

    kiwi2

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    Thanks John. The only reason I was looking at silicone is that Keith Appleton seemed to suggest they were OK in his video. Viton is going to be easier to source.
    Thanks for your comment Kitson. I think I'll go with viton O rings to start with, and if I strike problems, it won't be a big deal to change the pistons.
    Regards,
    Alan
     
  9. Dec 17, 2018 #9

    dazz

    dazz

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    Hi
    I suggest Turcon Variseal M2 type made by Trelleborg.
    The key specs are:
    300 deg C
    linear speed 15m/s
    pressure 20MPa dynamic
    Sizes range from 6mm to 3,300mm
    Single acting (two are needed on a double acting piston).
     
  10. Dec 18, 2018 #10

    kiwi2

    kiwi2

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    Thanks Dazz,
    The engine I'm looking at is double acting and I'm a bit limited by the depth of the block. I don't think I could fit a double grooved piston in the space available.
    Regards,
    Alan
     
  11. Dec 18, 2018 #11

    dazz

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  12. Dec 18, 2018 #12

    Jasonb

    Jasonb

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    Dazz, how do you fit those seals to a steam engine piston? they look to be made to go into a groove cut in the cylinder to seal a shaft as you would not be able to stretch the internal spring over a piston. Also as they are for hydraulics do they create a lot of drag at low air and steam pressures?
     
  13. Dec 18, 2018 #13

    dazz

    dazz

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    Hi
    I haven't used them but I plan to. There is a lot of stuff on the internet about using DIY PTFE rings. A key issue is that the rings expand a lot with heat, so this expansion has to be accounted for when sizing the ring/bore. Friction will depend on the fit. Some experimentation will be required.

    The rings will stretch over the piston.

    The big advantages with these is that they don't rust and they are relatively cheap. They won't scour the cylinder.
    The upper temp limit could be a problem with super heated steam.

    Dazz
     
  14. Dec 18, 2018 #14

    fcheslop

    fcheslop

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    The Turcon Glyd ring maybe a better alternative if you want to go down that route
    Iv used them on many applications operating at around 7 bar steam pressure and for piston seals in abrasive environments at around 100c
    The humble O ring works well enough for my simple needs
    Iv modified a D10 to use ptfe cup seals just two back to back as per a bicycle pump
    Only been a rough ars**d service engineer to fit the Turcon rings simply pop them in boiling water and they will stratch over the piston ,To get them into the bore use a home made piston ring compressor usually a bit of tin and a jubilee clip will suffice or if you want to be posh make a tapered sleeve
    This site has some good info on making cup seals from ptfe for small steam engines
    http://www.vapeuretmodelesavapeur.com/accueil/index.html
     
    Last edited: Dec 18, 2018
  15. Dec 18, 2018 #15

    dazz

    dazz

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    Hi
    The reason I intend to go down the commerial-off-the-shelf seals is that they will have chosen materials fit for purpose.
    Clearly plain PTFF and other plastics will work as DIY rings.
     
  16. Dec 18, 2018 #16

    fcheslop

    fcheslop

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    As with all things theres more than one way to skin a cat.
    Good luck with youre build
    kind regards
     

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