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Thread: Boiler Pressure

  1. #1
    Senior Member specialpants's Avatar
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    Boiler Pressure

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    This question is just out of curisoity and I have no intentions of making changes to my machine.

    What happens when the boiler hits the red zone? I assume the temperature is much hotter and the steam/hot water would exit with greater force, but what are the adverse affects to the machine (eg pipes, seals etc)?

    Does the whole thing blow up (http://coffeesnobs.com.au/YaBB.pl?num=1284516145)?

    The other question are:
    If the machine pumping out espresso at 9 bars, does this mean the brew boilers pressure is at 9 bars?

    At what pressure will the safety relief valve activate? How do I test it and know it is working? Andy said something about a spoon test - but I cant figure this one out. The pressure relief valve looks like something youd pull up rather than push down with a spoon.

  2. #2
    Senior Member Pavoniboy's Avatar
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    Re: Boiler Pressure

    Quote Originally Posted by 292A3F39333B362A3B342E295A0 link=1318119780/0#0 date=1318119780
    What happens when the boiler hits the red zone?

    You pray your safety release valve is working - unlike in the machine in the link. Or you notice yourself before it blows, and quickly turn it off and call a technician.

    Quote Originally Posted by 292A3F39333B362A3B342E295A0 link=1318119780/0#0 date=1318119780
    If the machine pumping out espresso at 9 bars, does this mean the brew boilers pressure is at 9 bars?
    No, the 9 bar is achieved via a pump, not the pressure in the boiler. In a HX machine which most cafes run, the water for the espresso pour is not even from the boiler. In a dual boiler where the pour is from a boiler - the 9 bar is still achieved via a pump not the boiler itself.

  3. #3
    Site Sponsor coffee_machinist's Avatar
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    Re: Boiler Pressure

    Most domestic boilers are pressure tested to around 6 bar, safety valves are designed to release somewhere between 2 and 3 bar but have an adjustment range set via spring pressure.

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    Senior Member specialpants's Avatar
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    Re: Boiler Pressure

    Cheers for the replies. Good to know theyre safety tested to 6bar.

    As for the 9bar brew thing. Yes, the pressure is achieved through the pump, but doesnt it mean the whole system is pressurized at 9bar? ie everything between the pump and the shower screen.

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    Re: Boiler Pressure

    Quote Originally Posted by 4340555359515C40515E4443300 link=1318119780/3#3 date=1318916426
    Cheers for the replies. Good to know theyre safety tested to 6bar.

    As for the 9bar brew thing. Yes, the pressure is achieved through the pump, but doesnt it mean the whole system is pressurized at 9bar? ie everything between the pump and the shower screen.

    This has sparked my interest too - Ive just done a quick google to try to find a typical espresso pump/boiler circuit schematic but came up with nothing - does anyone have something they can post here (single or double boiler, HX?) that I can take a squiz at?

    Cheers, Mick

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    Senior Member specialpants's Avatar
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    Re: Boiler Pressure


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    Re: Boiler Pressure

    From my understanding of pumps (not specific to espresso machines) the system will be pressuries post pump outlet, to achieve a pressure of 9bar at the portafilter. The pressure loss through the pipes etc would mean the pump is actually producing a higher pressure than 9bar.

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    Re: Boiler Pressure

    My Giotto shows 1.1-2 BarG, 2.1-2 BarA, (0.21 MPaA) on its pressure gauge, this equates to a saturated steam and water temperature of 123 degrees C, this is from steam tables.




    The boiler isnt a good pressure vessel shape, being flat ended.


    The safety valve "Should" have been sized to allow the full steam production of the boiler out with an acceptable pressure rise above the cracking pressure of the safety, or this is normal steam practice at least.

    This is a 6MPa (900 PSI) ships boiler, everything that can be made round or cylindrical is, as this is a good pressure vessel shape.


    As is the body of a My pressi twist.


    So if you trust engineering, then all is well, even if the element control sticks on, it shouldnt go bang, just do lots of expensive damage.

    BTW, a Bar is 10 to the 8th pascals, and is frowned at as not being in the 3, 6, 9.... progression of metric quantities, so MPa, megapascals, or 10 to the 9th, is preferred.
    One Bar, is close to one standard atmosphere, hence its continued use, but it can make calculations harder.
    A Pascal is one kilogram mass, being acted on by a standard gravity, 9.81 M/s2, which translates into one newton of force, acting on a piston of 1 meter square in area, and so is a small pressure, hence the need to add lots together, but it is derived from metric base quantities, and so good in the SI eyes.

  9. #9
    Member mtee's Avatar
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    Re: Boiler Pressure

    Quote Originally Posted by 494A5F59535B564A5B544E493A0 link=1318119780/0#0 date=1318119780
    The pressure relief valve looks like something youd pull up rather than push down with a spoon.
    Thats the anti-vacuum valve.

    Coffee Parts have a section on their website where this kind of stuff is explained, its well worth a read.

  10. #10
    Senior Member Pavoniboy's Avatar
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    Re: Boiler Pressure

    Quote Originally Posted by 7F505A4713795F5A595B4A3E0 link=1318119780/7#7 date=1322492167
    This is a 6MPa (900 PSI) ships boiler
    Wow, there must be a lot of coffee drinkers on that ship! :D

  11. #11
    KJM
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    Re: Boiler Pressure

    Quote Originally Posted by 5D6C7B6263646F62740D0 link=1318119780/9#9 date=1322551539
    Wow, there must be a lot of coffee drinkers on that ship!*
    Never mind that, you should see the portafilter ;D

    /Kevin

  12. #12
    Mal Dimal's Avatar
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    Re: Boiler Pressure

    Ah, what can you say.... ::)

    Big boys and their (big) toys... ;D

    Mal.

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    Re: Boiler Pressure

    Some other figures from the boilers, producing 18,000 kW at the propeller, from 80 tonnes of steam an hour, at 515 degrees C.



    One burner, of four, burning liquid natural gas boil off from the cargo tanks, 128,000 cubic meters, called BOG, boil off gas, and the boilers can run on horribe black heavy fuel oil as well, no photo of this as it is VERY bright.

    One of the boilers,


    Coffee content!!!!!

    This is the bridge instillation.


    But I dont use the thermoblock POS, I use one of these.



    For a good short black.

    As the boilers provide the steam for our main turbo alternator, 2.7 MW, and this power drives the ZIP boiler I get my hot water from, than it can be said that the system is a fully steam powered one.

    Original purpose of the post is to say that the safety valve is sized to protect the system from over pressure, and our boilers have two on each drum, so that they together can flow 40 tonnes of steam an hour, and so should the safety on your machine, just a bit smaller :-)

    I had my Giotto lift its safety when the "black box" died for the second time, as the element control stuck on (this is before the new way of wiring it in was done) and did its job, with the pump topping up the boiler drum until muggins here noticed, and shut it down.
    No damage done, and the safety reseated fine.

  14. #14
    enjoy black coffee JamesM's Avatar
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    Re: Boiler Pressure

    holy sh1t!!! :o

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    Re: Boiler Pressure

    Behmor Brazen - $249 - Free Freight
    Quote Originally Posted by 6B6A6D200 link=1318119780/10#10 date=1322644401
    Never mind that, you should see the portafilter
    Heres the cup they use.


    Java ";D" phile




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