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Thread: Teflon Tube(PTFE) keep blowing up (from pump to heat exchanger)

  1. #1
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    Teflon Tube(PTFE) keep blowing up (from pump to heat exchanger)

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hello experts!

    I am asking for a expert's advise on my leaking la nuova Cuadra(Diamond Italy)!

    Have opened up the machine, found a tube blown up going from pump to heat exchanger.

    I have purchased the genuine part from the original supplier, which was teflon(PTFE) 4x6mm tube, and it was okay for 3 days and blown up again.
    So have sourced another one, and the same thing happen. it blown up again in few days time.

    So I did some research on Teflon Tube(PTFE), and it should hold up to 60 bar pressure, with 220C temperature. I think heat exchange would only go up to 15bar maximum and 100C temperature being it's water?, but as Photos below, its blown up. and I could not really understand why as the pressure and temperature is well lower than what the Teflon tube could resist.

    Only possibility that I could think of I may snapped the tube while I install so it has the weak point, but I believe I did not snapped or fold it at all...



    Not sure how I can attach photo from here, so sharing below google photo link

    https://photos.app.goo.gl/dpn5WQvREURoKemx6
    https://photos.app.goo.gl/PtCBKD3B8aZgmBpJ9

  2. #2
    Mal Dimal's Avatar
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    Hmmm...

    Never seen that before.
    Maybe your supplier has been provided with a faulty product??

    May have to wait until one of our Pros comes across your thread and can offer an opinion...

    Mal.

  3. #3
    Senior Member Jackster's Avatar
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    I was thinking it was heat. But you say it's the bottom pipe in the pic?
    At least it's 6mm and easy to get.
    I just had some thinner stuff that needed a flared end. I managed to get it to flare with gentle flame

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    There looks to be some serious scale around some of the joints which leads me to think there is some block causing the pipe to go over pressure somehow. It’s definitely a blow out. Did the machine function ok when you first put it in

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    Quote Originally Posted by Fuelledbycoffee View Post
    There looks to be some serious scale around some of the joints which leads me to think there is some block causing the pipe to go over pressure somehow. Itís definitely a blow out. Did the machine function ok when you first put it in
    Thanks, yes it worked perfectly for 3-5 days or so.. and blown up.. would descale fix the issue or should i get new joint parts?

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    Quote Originally Posted by Dimal View Post
    Hmmm...

    Never seen that before.
    Maybe your supplier has been provided with a faulty product??

    May have to wait until one of our Pros comes across your thread and can offer an opinion...

    Mal.
    Thanks Mal
    I have asked the supplier but they said no issue from their end... no way to prove though
    Dimal likes this.

  7. #7
    NJD
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    Is it possible that this teflon tube is touching some hot pipework and thus weakening the strength of the pipe wall allowing a pressure buildup to casue the rupture of the pipe ? That looks very plausable by the look of the picture of your tube failure.

    Just thnking out loud mate Good luck

  8. #8
    Mal Dimal's Avatar
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    I don't think there would be anything "under the bonnet" that gets hot enough to do that to genuine PTFE tubing. Perhaps the tubing is Nylon rather than PTFE - They can look similar...

    Mal.

  9. #9
    Senior Member Lyrebird's Avatar
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    Quote Originally Posted by efuu00 View Post

    So I did some research on Teflon Tube(PTFE), and it should hold up to 60 bar pressure, with 220C temperature.
    Either, but not both. 60 Bar will be at room temperature, at 220 oC the tube will have no strength.

    The burst pressure for tube is given by tensile strength x internal radius / wall thickness. Your 6 x 4 tube has an internal radius of 2mm and a wall thickness of 1mm so the burst pressure is tensile strength / 2

    For extruded PTFE the theoretical tensile strength is around 12 MPa* at 0 oC so the burst pressure for your tube will be around 6 Mpa (approx 60 Bar). At 121 oC it declines to 3.4 MPa* so the burst pressure would be around 1.7 MPa (approx 17 Bar).

    No engineer ever specifies a material at its maximal strength, it's normal to apply a safety factor of at least x 3, so the working pressure of that tube at 121 oC should be about 0.5 MPa (5 bar).

    BTW 121 oC is used because it's the temperature at which an autoclave operates when the internal pressure is 1 Bar. The internal temperature of a coffee machine boiler is usually a bit higher than this.




    * Figures sourced from Dupont PTFE Properties Handbook p12
    Last edited by Lyrebird; 10th December 2018 at 02:42 PM.
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