Krytox grease as a piston seal lube

Discussion in 'Piston & Spring' started by Bernard Todd, May 27, 2019.

  1. Bernard Todd

    Bernard Todd New Member

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    Has anyone ever used krytox GPL 205 grease on piston seals, it is as far as I can make out expensive, meant as a lubricant for synthetic material and non flammable, it should not diesel in springers, but at £40 for 2oz is not something I will try on a whim. Any body tried this as a piston seal lube.
     
  2. Nick G

    Nick G Active Member

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    Its very good and will not diesel in standard or mildly tuned guns , however if you push the boundaries , it will burn. Finish line bike grease works equally as well and is a fraction of the price .
     
  3. RobF

    RobF Administrator Staff Member

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    Not sure where this comes from as the technical specs (used in engineering) say it does not and cannot burn.

    Hyrdrocarbon Lubricant Catches On Fire

    DuPont Performance Lubricants for Maintenance, Repair and Operations

    It would be suicide for DuPont to offer a product in those industries and to say it didn't burn if it did.
     
  4. Andrew Barnes

    Andrew Barnes Barnes II

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    I know a bit about Krytox as we use "lots" of the stuff at work for Oxygen valves, and its a bit of a pet topic, apologies in advance for my ramblings.... Right so there are two aspects to lubrication, however before the science starts......if all the giggling girls would like to leave the room now as there will be quite a few potential "double entandras" in this post. Two aspects to lubrication first; trilogy, i.e. how the "lubricant" performs in terms of reducing friction and wear between two mating surface under a dynamic or static load, lets park that rather large topic for now.....2nd compatibility of the lubricant with the materials being lubricated and the environment in which the lubrication is required......now this is why Krytox is expensive.....Krytox was developed by DuPont for NASA as a "oxygen compatible" lubricant, its based on halogenated chlorotrifluoroethylene (CTFE), its specifically not a hydrocarbon based grease which pretty much everything other lubricant is, the point of this being given that as its not hydrocarbon (HC) based its does not readily burn or ignite in pure oxygen, as one may use in an Apollo rocket for example. So now how does this relate to PCP's, and springers well the first notable difference is we don't shot pure O2, we use a 20/80 oxygen /nitrogen mix, which massively reduces the risk of combustion. To ignite a HC in a diesel engine its needs to get hot before it ignites, so engine spins air diesel is injected and compressed, critically at this point it gets hot and then ignites expands..round and round we go....For a gun it would be very difficult to get an ignition event as whatever you are doing is a single event so no significant heat can build up. However if we now consider compatibility of the thing being lubricated, see extract from EIGA 13/12 (EIGA is European Compressed Gas Users Association, they have loads of freely available information this is from document 13/12 Oxygen materials, if you google you will find).

    • CTFE fluids should not be used with components fabricated from aluminium alloys under conditions of high torque or shear because of the danger of reactions with freshly exposed surfaces.
    • Care shall be taken with the selection of oxygen-compatible lubricants because, depending upon the application, the lubrication properties of CTFE fluids are generally not as good as hydrocarbon-based mineral oils or greases.
    So in summary, if you want to spend your money on Krytox that fines, Krytox is like a fine wine and it is very good stuff for the right application, but it might not be best lubricant for your application, as a general rule I would stick with OEM recommendation or if none given just get a good lubricant that compatibility with the O ring material
     
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  5. Bernard Todd

    Bernard Todd New Member

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  6. Bernard Todd

    Bernard Todd New Member

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    Thanks Andrew for the comprehensive reply, it answers my question, now I have the info I will get my hands on a small amount and experiment, I just love the experiment side of springers, it will take a wee while, I will post my findings. Thanks to all who contributed.
     
    Andrew Barnes likes this.
  7. RobF

    RobF Administrator Staff Member

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    Just to add, I've been using this for about 2 years now, it seems to work ok.
     
  8. Nick G

    Nick G Active Member

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    I appreciate what you are saying, and the du pont blurb, However I have seen the smoke , with both krytox and ultimox , when I had too much spring testing 21mm and 22mm tunes, so something was burning o_O.
     
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  9. RobF

    RobF Administrator Staff Member

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    It wasn't the lube ;)

    They could not get away with stating something didn't burn even in 100% 02 if it did. There's all sorts of enviroments where it would (not could) result in catastrophic accidents if it was the case.
     
  10. Andrew Barnes

    Andrew Barnes Barnes II

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    I tend to agree with the last post, it wasn't the lube. A bit more on the topic.....when selecting lubricant for high pressure oxygen systems there are two go-to places for information, 1st is the BAM list, and 2nd ASTM G63 both of these have materials properties listed for all the common O2 lubricants. From ASTM G63 the Auto-Ignition Temperature (AIT) for all the Krytox grades tested its >427degC (in pure O2) BTW this is the max temperature the test can go to. The compares to say 120-200degC for common hydrocarbon type lubricants. The other thing to note is that is for total combustion, which may be different from a bit of smoke!!!.

    One last point before this gets way beyond the scope of whats useful for most air gun shooters.....the issue with lubricants in O2 systems is not the combustion of the lubricant but that this starts a chain reaction; lubricant ignites, which in turn ignites to non metallic o ring, which then in turn ignites the metal at which point we are heading for a catastrophic loss of containment, this is the so call kindling reaction. The point with the O2 grease is that if they do ignite they release very little energy and therefore do not lead to the kindling reaction. See below extract from ASTM G63, note GPL 205 not listed but they are all very similar in composition.
    Krytox ASTM G63.PNG
     
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  11. Nick G

    Nick G Active Member

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    I too use it, and have been for around 5, years, I was just stating that in some circumstances, I can and do end up with the smoke, and velocity drop ( you get the smoke, the drop , then re lube and the power comes back up for a couple of shots suggesting the lube has disappeared ),its generally when something isn't sealing or too much spring/piston weight/ not enough volume , in small diameter comp tube tunes . Once its all set up and working correctly it doesn't happen.
    Its rare .
     

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