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Thread: relation between pressure & temperature

  1. #1
    Senior Member summercrema's Avatar
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    relation between pressure & temperature

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    I was talking to a Espresso Machine technician yesterday about consistant temperature on Espresso machine, he told me commercial machine generally has a 9 to 10 bar pressure and the machine water temperature should be hot enough for making espresso without burning it, it is default from factory and need not be adjusted. Can someone explain to me actually how does pressure control the water temperature? thanks

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    Re: relation between pressure & temperature

    pv=nRT ...from a very distant past life.

    Increase pressure, increase temperature...directly proportional. Not sure how that applies in this circumstance though...Im sure someone does.



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    Sleep is overrated Thundergod's Avatar
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    Re: relation between pressure & temperature

    To me, in a coffee machine the pressure and the temperature are two seperate issues.

    He is right, he temperature of the water should not burn the coffee.

    The pressure of the pump should push 9 bar of water pressure through the coffee.






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    Re: relation between pressure & temperature

    Hi summercrema,

    You can apply smokeydecks formula to the boiler water temperature and pressure. Increase boiler pressure - increase boiler water temperature. The pressure you mention is the brew pressure which is a separate thing,

    charlie

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    Senior Member GregWormald's Avatar
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    Re: relation between pressure & temperature

    I seem to remember Charles Law and Boyles Law relate to this--usually called Charlie Boyles Law cause no-one could remember which was which. High school physics was a long time ago. :P

    Greg

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    Re: relation between pressure & temperature

    Quote Originally Posted by summercrema link=1228893792/0#0 date=1228893792
    I was talking to a Espresso Machine technician yesterday about *consistant temperature on Espresso machine, he told me commercial machine generally has a 9 to 10 bar pressure and the machine water temperature should be hot enough for making espresso without burning it, it is default from factory and need not be adjusted. Can someone explain to me actually how does pressure control the water temperature? thanks
    What everyone else said.

    Anecdotally, with some prosumer HX machines, at least, a change of about 0.1 bar gets you a change of about 2 degrees C at the head after it has stabilised. I have no idea of the extent to which that applies across different HX machines and I dont care to speculate. But it gives you an idea.

    Sounds like the tech either tells people not to adjust temp/pressure because he thinks that a lot of people will cause damage to themselves or their machines (might be right; hes the tech; hed know) or he doesnt really have that great a knowledge of espresso.

    Cheers,

    Luca

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    Sleep is overrated Thundergod's Avatar
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    Re: relation between pressure & temperature

    I think you might consider changing that from anecdotally to fact if you ask Chris.
    When he was up at Cuppacoffee adjusting a few machines Im pretty sure thats what he did on a few.

    As my Expobar has crept up a smidge over the last two years and is currently running a tad hot, he recommended I adjust it down about 0.1 - 0.2 and that should knock a few degrees off.

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    Re: relation between pressure & temperature

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    Quote Originally Posted by summercrema link=1228893792/0#0 date=1228893792
    I was talking to a Espresso Machine technician yesterday about *consistant temperature on Espresso machine, he told me commercial machine generally has a 9 to 10 bar pressure and the machine water temperature should be hot enough for making espresso without burning it, it is default from factory and need not be adjusted. Can someone explain to me actually how does pressure control the water temperature? thanks
    Yeppers- all good...Except for the fact that the majority of machines my PF pressure gauge gets to test are more like 11-12 bar. In fact, the only exceptions I can think of which arrive at 9 bar from the importer/s are Rocket and the Diadema Junior Extra.

    Temperature is directly related to pressure and one of the more accurate ways to see whats going on at the group is with a Scace and a good datalogging thermometer and software. Say goodbye to a gorilla to buy all the gear...

    Chris



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