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High pressure rotary seal design, ideas welcome

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  • High pressure rotary seal design, ideas welcome

    As my wire EDM is almost operational again with the version 2 controller, I'm starting to warm up my old project of making a small hole EDM or drill EDM. That will have a rotary spindle with a maximum of 100 RPM and I need to get water through the spindle at 5-10 MPa (50-100 bar).

    Commercial solutions exists, such as Deublin connectors, but the price is more than I like at the moment, so I'm off to trying to design my own.

    As the media is water, the parts have to be machined out of brass, aluminum or stainless. I was thinking of making a shaft with a radial hole in it and then a stationary ring that has seals in it that will ride on the spindle on polished surfaces.

    I'm just a bit unsure of what seals to look for that would handle the pressure needed and not be stupidly expensive. Any suggestions?
    Amount of experience is in direct proportion to the value of broken equipment.

  • #2
    Hose coupling off a keratcher pressure washer, it swivels I believe
    Mark

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    • #3
      Originally posted by boslab View Post
      Hose coupling off a keratcher pressure washer, it swivels I believe
      Mark
      Swiwels, yes, but is not designed for constant rotary motion.
      Amount of experience is in direct proportion to the value of broken equipment.

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      • #4
        Not sure what the costs involved would be but have you looked into using a mechanical carbon seal?

        These are available in a wide range of sizes and styles. I know they are capable of high pressures and are used with a wide variety of fluids.
        They also are very durable and enjoy a long life.

        I have rebuilt large fuel transfer pumps using these and have always been impressed with their simplicity and long life. Used on water and propane transfer pumps a lot.

        http://www.pumpseals.net/carbon.htm
        Home, down in the valley behind the Red Angus
        Bad Decisions Make Good Stories​

        Location: British Columbia

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        • #5
          For pressures above 50 bar you may have to go to PTFE seals.

          See:
          www.parker.com

          Good design documentation.

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          • #6
            Most Ag Combine Harvesters have a hyd swivel that attaches to the shaft of Rotor Drive shaft,they run in excess of 1000 rpm and must be in that 3000 psi range.I beleive the hose is 3/8" that feeds it

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            • #7
              A carbon face seal will be a useful choice for water at pressure.

              http://www.deublin.com/products/rotating-unions/

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              • #8
                I used to use Deublin rotary unions on machines I built. They were actaully amazingly low cost for how they were made, and extraordinarily reliable too.

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                • #9
                  Originally posted by garyhlucas View Post
                  I used to use Deublin rotary unions on machines I built. They were actaully amazingly low cost for how they were made, and extraordinarily reliable too.
                  I've seen them run for quite some number of years while pushing glass laden mineral oil and glass laden water soluble applied to diamond core drilling of sheet glass substrate.

                  I would bet they would have comment on the pressure requirement as well. Give a call to their applications engineer.

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                  • #10
                    What you are looking for is a Mechanical Seal, simple versions for relatively low pressure water systems are often a ceramic ring rotating against a viton O ring for the moving interface, there may well be a suitable composition of O ring or seal material for your application,

                    - Nick
                    If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

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                    • #11
                      1500 psi (around 100 bar) isn't that high. The rotational speed is what will destroy your seals.

                      Construction excavators utilize a rotary manifold for the track drives. Most of these systems operate around 4000 psi (275 bar). I would try what they use - a o-ring engaged against a PTFE ring. Don't plan for 100% sealing - you are going to have some leakage through a case line. Of course this is for hydraulic oil. Certain seal materials do not like water and will significantly expand, which in this setup will drive up the friction in the manifold and destroy your seals. You are trying for less than 5% squeeze on the o-ring - maybe even lower to keep the friction down. Any expansion of the seals will drive this value up and rip out the o-ring seal.

                      The ceramic suggestion above is a good one, but may not be available for making in the home shop? I haven't looked.
                      www.thecogwheel.net

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                      • #12
                        This is actually a std product in some VMCs with through spindle coolant.

                        Its a carbide ring, against a hardened steel face.
                        Haas does/did it like this.
                        Should be simple to homebrew, source the carbide ring (20-40$ ??) and or a hardened steel ring, lap both flat with CI / brass / alu laps.

                        Lap *Not* against each other, but real soft laps with diamond grit/liquid suspension.

                        When really flat, they don´t leak, and I think the clearance is about / less than 1 micron.
                        And up to 10-15.000 rpm on VMCs.
                        You could countersink the seal pieces into the surfaces, maybe.

                        Use something like hysol locktite 3784 to mount, imho.
                        A heat gun could then take the seal pieces off for rework, no damage.

                        Hand work on a cast iron lapping plate should work, imho.

                        You are not trying to make the pieces really flat or really accurate, you are trying to get them to conform extremely well.
                        This means e.g. bow/saddle shape is not a concern, not is actual shape/size/thickness.

                        Amateurs make telescope mirrors, by hand, in lenses and optical flats to 10-50x better accuracies, all the time.
                        Thus it cannot be all that hard or expensive, and lots of lapping youtube videos and astronomy stuff exists.

                        These are called (sealless ?) rotary unions, and last a long time in commercial use.
                        It may be you must have pressure on at all times, when using it.


                        I remember I was surprised when I heard about how it works, around 2012.

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                        • #13
                          I'd try a GH profile PTFE piston seal, they should be fine with a bit of rotation and they can definitively handle the pressure and water.

                          http://www.skf.com/group/products/se...ata/index.html

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                          • #14
                            Just google

                            Rotary seal design guide catalog cps 5350

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