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Thread: Heat Exchanger TOO HOT!!

  1. #1
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    Heat Exchanger TOO HOT!!

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    I have just done up a La Pavoni Pub and it is way too hot at the group head.
    The boiler is set to 1 Bar but if its left on for a while you need to flush this machine for a long time before the group temp comes down. (timed results below)
    I would appreciate any tips or advice.
    Thanks
    Cam

    I just timed my machine to get more accurate results:
    From cold to boiling - 13 minutes (4 ltr boiler)
    Boiling to 1Bar pressure - 5 minutes
    30 seconds later the temp was 96 deg at the group!
    2 minutes later I timed the flush. It took 6 minutes to come down from 97 to 92 degrees!

    A long time to wait for one coffee!!


  2. #2
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    Re: Heat Exchanger TOO HOT!!

    Have you actually tried a coffee from it (without the extended cooling flush)?

    Group temperature is not the be all and end all, and besides, unless youre using a fully calibrated measuring device to check the temperature you cant be sure that your measurements are reflective of reality (for example, a K-type thermocouple is accurate to +/- 2.5 degrees C for most of its range (+/- 5 for other parts of its range IIRC) but if its uncalibrated thats meaningless as it may (and quite likely does) read zero when it is not actually at zero).

    In short, let your pallate guide you, if it tastes good leave it alone, if its not, look at lowering the pstat setting a bit.

  3. #3
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    Re: Heat Exchanger TOO HOT!!

    That is a good reality check. thanks
    It does actually taste slightly burnt but I will also try some different beans.

    I am measuring the water with a new digital thermometer that does seem accurate. it reads 98 to 99 degrees when I hold it in the water as it exits the group head. You can see it bubbling and hear it hissing so I know it is boiling as it comes out!

  4. #4
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    Re: Heat Exchanger TOO HOT!!

    It is interesting that if I check the temp without flushing the water is around 92 deg for about 10 seconds and then heats up!
    I guess the group is the right temp but the heat exchanger is too hot.
    Is this normal?

  5. #5
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    Re: Heat Exchanger TOO HOT!!

    If you have water flash boiling on exit then its a pretty good bet that its running hot.

    Im not particularly familiar with these machines, but given your description its probably worth dialing back your pstat to ~0.9bar and seeing how it goes.

  6. #6
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    Re: Heat Exchanger TOO HOT!!

    All my temperature readings were taken with the boiler set to 0.8 Bar!
    I just talked with a coffee technician who thinks that a restrictor might be missing in the thermosyphon loop.
    Apparently there should be one in the group head and one at the top of the heat exchanger.
    I will check in the next couple of days.
    He also told me I shouldnt go below 1 Bar for boiler pressure.
    I will try one thing at a time I guess!

  7. #7
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    Re: Heat Exchanger TOO HOT!!

    Quote Originally Posted by 56545875585659350 link=1341102242/3#3 date=1341197309
    I guess the group is the right temp but the heat exchanger is too hot.
    Is this normal?
    Yes. ! normal.
    On a HX machine that has been at idle a few mins, the brew water in the HX tube will be close to boiler temp (120+ C) .
    The Group will always be cooler since although part of it is heated by the HX water, most of it is hanging out in the breeze !
    The traditional "HX cooling flush" is a method of flushing this "overheated" water out, before using cooler water to extract the shot.
    The thermo syphon restrictor will effectively keep the group a little cooler still.

  8. #8
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    Re: Heat Exchanger TOO HOT!!

    I just found out that the boiler pressure measurement is based on the max pressure when it cuts out, so mine was actually set to 1.1 Bar.
    I have reduced it to 0.9 which has helped slightly.
    I only have to wait 2 minutes for the temp to come down now.
    it still steams the milk ok, just bit slower.

    I dont seem to have any restrictors in the line from the heat exchanger to the group so will try that next!
    Any ideas how I can make one?

  9. #9
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    Re: Heat Exchanger TOO HOT!!

    Another issue has just arisen!
    the flow rate has just doubled to the group head with a noise that sounds like a slightly open tap (hissing).
    Maybe something has come loose inside the group head.
    Any ideas anyone?

  10. #10
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    Re: Heat Exchanger TOO HOT!!

    Possibly your 3 way solenoid valve was sticking or partly clogged with loose scale and has just cleared itself ?

  11. #11
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    Re: Heat Exchanger TOO HOT!!

    I worked my way back from the group head trying to isolate the noise.
    With the pipe disconnected from the group head I ran some water slowly and heard more of a rattle. it is somewhere before the heat exchanger.
    Will keep going with my investigations!

  12. #12
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    Re: Heat Exchanger TOO HOT!!

    the rattle was a ball bearing in the water inlet valve but I dont think that is the issue.
    The pump is making an unusual noise too!
    Maybe that noise is travelling up the pipes??
    The pump is also pulsing. you can see it on the pressure gauge.
    I think I need some sleep and rethink it all in the morning.

  13. #13
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    Re: Heat Exchanger TOO HOT!!

    Ok, I purchased and installed a restrictor in the top of the heat exchanger and it seems to have worked!
    I think I can turn up the boiler pressure now.

    The pump is still pulsing but I dont think this is effecting the flavour of the coffee.

    Time to enjoy some coffees!

    Thanks to all that have made comments.
    It is appreciated.

    Cam



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