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Giotto Pressure cycle for steam

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  • krusty
    replied
    Re: Giotto Pressure cycle for steam

    someone asked about the steaming and minoreII.... well, this morning i thought i would test it a little with my minore I.... my understanding is that both the machines are pretty much the same in this area...

    well, it sits at about 1.1, and dropped to about 0.9 when i started steaming..
    after 40 secs or so, the boiler light came on, and the needle wavered a little, but was pretty much at 0.9... another 40 secs and i was getting a bit wet from the condensation so i stopped.... but the preassure didnt seem to move from 0.9.



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  • TC
    replied
    Re: Giotto Pressure cycle for steam

    Another good reason to have a working anti vac valve in my opinion....

    2mcm

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  • Andy-Gadget
    replied
    Re: Giotto Pressure cycle for steam

    To return to the "dont steam at under 0.5 bar boiler pressure" thread, On reflection I thing this is a worst case situation, and is realy driven by the temperature of the milk.

    Consider this, If you start texturing COLD milk with the boiler at less than 0.5 bar, then the cold milk will be condensing the steam very well. with a restriction (the valve) in the steam line, then it is very possable to pull the milk up the wand.

    The original Newcomen steam engine was realy a vacuum engine, and the vacuum was created by condensing the steam, see http://en.wikipedia.org/wiki/Steam_engine

    All it would take to pull milk back into the boiler from this is for the "auto fill" to start, dropping the boier pressure even further and so milk in the boiler.

    This would probably happen at a pressure a lot less than 0.5 bar, but ECM have applied a "Bugger factor", also known as a "factor of ignorance" to this, and decided that 0.5 bar is safe.

    On a tangent, the water level in the boiler acts in the reverse of the steam demand, that is, when steam is drawn off the boiler, the pressure drops, the water level in the boiler actually goes up, this is know as "Swell", and when the steam demand is reduced, the pressure increases and the level drops, this is known as "Shrink".
    What is driving this is the volume of water displaced by the steam forming around the element, at lower pressure the bubbles are bigger and so displace more water, raising the level.

    The boilers I am working on now produce 80 tonnes of steam an hour at 6 Mpa (900 psi), but only contain about 14 tonnes of water in the whole system, so boiler level control is both complex and essentual, and is probably the most complex system on the ship.
    Boilers look simple, until you start to to look closely at them, then they are very complex indeed.

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  • TC
    replied
    Re: Giotto Pressure cycle for steam

    Originally posted by Curmudgeon link=1175907475/15#22 date=1176295079
    Not sure on that. If you pull a shot at the same time as pulling steam, you are still not lowering the boiler water level...simply lowering the boiler pressure much more quickly due to the heat exchange going to the brew water.

    Yes this will kill the boiler pressure much more quickly, but it wont necessarily result in an auto fill.

    I assumed the question concerned pulling steam while not running the group. Could be my mistake.

    Does any one really try and pull coffee and steam at the same time with these little babies????????? I know its a selling point but............
    Yeppers- all the time.....Theyre designed to do it....

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  • Thundergod
    replied
    Re: Giotto Pressure cycle for steam

    I do with my Expobar.
    Arent they similar?
    Their steaming ability seems to be.

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  • Curmudgeon
    replied
    Re: Giotto Pressure cycle for steam

    Not sure on that. If you pull a shot at the same time as pulling steam, you are still not lowering the boiler water level...simply lowering the boiler pressure much more quickly due to the heat exchange going to the brew water.

    Yes this will kill the boiler pressure much more quickly, but it wont necessarily result in an auto fill.

    I assumed the question concerned pulling steam while not running the group. Could be my mistake.

    Does any one really try and pull coffee and steam at the same time with these little babies????????? I know its a selling point but............

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  • TC
    replied
    Re: Giotto Pressure cycle for steam

    Originally posted by Curmudgeon link=1175907475/15#20 date=1176292901
    Cant see why the pump would kick in at all.

    Steaming milk causes a pressure drop not a water level drop that would be so large as to result in the auto fill kicking in, except if the water level was already low......& you cant pick where that might be at any particular time.

    All you can say as far as "normality" is concerned, is that as soon as you crack the steam tap open hard the pressure drop in the boiler should result in the element switching on immediately.  Anything else happening around the same time is pure coincidence.

    If you instead fill your 600 ml jug to 1/2 instead of 2/3, the situation will change especially as you wont pull as much capacity out of the boiler at once. Somewhere between 1/3 and 1/2 a 600ml jug worth of milk is just the right volume for 2 standard size capps......it can be said that to ask a machine that size to froth any more in one lot, is to venture outside what might be called "reasonable" for such a machine and what it was designed to do by its ristretto drinking Italian designers.   The other side of the coin is because of their small size, they recover extremely quickly so there is no need to overdo the steaming.

    The other positive is if you steam less milk, you also get a better (more well textured) result.

    If worried about the pump kicking in while steaming, first pull hot water out of the tap to cause an auto fill to occur, wait for that to stop and then for the pressure to build back up and the elemt to cut out, then steam your milk. At that stage there will be far less likelyhood of the pump kicking in while your steaming.

    So I think the answer to the question  is...its all a matter of management.
    It may if you are in the process of pulling a shot whilst texturing...which is why we buy HX and dual boiler machines

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  • Curmudgeon
    replied
    Re: Giotto Pressure cycle for steam

    Cant see why the pump would kick in at all.

    Steaming milk causes a pressure drop not a water level drop that would be so large as to result in the auto fill kicking in, except if the water level was already low......& you cant pick where that might be at any particular time.

    All you can say as far as "normality" is concerned, is that as soon as you crack the steam tap open hard the pressure drop in the boiler should result in the element switching on immediately.  Anything else happening around the same time is pure coincidence.

    If you instead fill your 600 ml jug to 1/2 instead of 2/3, the situation will change especially as you wont pull as much capacity out of the boiler at once. Somewhere between 1/3 and 1/2 a 600ml jug worth of milk is just the right volume for 2 standard size capps......it can be said that to ask a machine that size to froth any more in one lot, is to venture outside what might be called "reasonable" for such a machine and what it was designed to do by its ristretto drinking Italian designers.   The other side of the coin is because of their small size, they recover extremely quickly so there is no need to overdo the steaming.

    The other positive is if you steam less milk, you also get a better (more well textured) result.

    If worried about the pump kicking in while steaming, first pull hot water out of the tap to cause an auto fill to occur, wait for that to stop and then for the pressure to build back up and the elemt to cut out, then steam your milk. At that stage there will be far less likelyhood of the pump kicking in while your steaming.

    So I think the answer to the question is...its all a matter of management.

    Leave a comment:


  • mr_fox
    replied
    Re: Giotto Pressure cycle for steam

    ahh that ecm website....no beer

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  • Thundergod
    replied
    Re: Giotto Pressure cycle for steam

    Either they were being overly cautious or amusing themselves.

    I was reading a testing document, for the Y2K program, that ran to hundreds of pages, when about 2/3rds of the way through I ran across a line that said something like "if you have read this far you owe me a case of beer".

    Well, not only did I point out to the writer that it was very unprofessional and that he should immediately revise the document and resubmit it, but I pointed out that if we operated that way it would be he that owed me the beer.

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  • TC
    replied
    Re: Giotto Pressure cycle for steam

    Yeah- You read some really interesting things in user manuals

    Theyre being way overcautious IMHO....All Giotti ship with an anti-vac valve on the boiler. Unless this failed andthe boiler was allowed to cool with a wand immersed in milk or other fluids, I cant see how youd suck nasties into the boiler. At any rate, as TG correctly states, we all know that 0.5 bar is positive pressure ...

    2mcm

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  • Thundergod
    replied
    Re: Giotto Pressure cycle for steam

    Interesting statement.

    At .5 bar the steam is still coming out of the wand.
    Thats positive pressure, definitely not sucking.

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  • mr_fox
    replied
    Re: Giotto Pressure cycle for steam

    ecm website states not to froth milk under .5bar as milk can be sucked up into your boiler..

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  • Myrtle
    replied
    Re: Giotto Pressure cycle for steam

    My machine had its first test yesterday - knocked out 10 milk coffees without any fuss at all. Like TG, it was me working up the sweat.

    Very happy with the end result.

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  • Dennis
    replied
    Re: Giotto Pressure cycle for steam

    Originally posted by Thundergod link=1175907475/0#10 date=1176003781

    As it is though the machine more than adequately keeps up with me.
    In my case its more a matter of me keeping up with the machine than the other way round

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