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  • #16
    Re: Back Flushing

    Originally posted by Fresh_Coffee link=1097923570/0#14 date=1103792093

    And just to set the record straight, point b) above is for COMMERCIAL design machines ie, those with heat exchangers, and the operator is "freshening" up BOILER water, which is NOT the water used to make coffee in these machines.
    Hey FC,

    I guess Im unclear by what you mean by the above quote as my Cimbali M28 only has the one boiler and all water used on it goes through the boiler. Including that used for pulling shots.

    Java "Flush baby, flush!" phile
    Toys! I must have new toys!!!

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    • #17
      Re: Back Flushing

      Java,

      it is more likely than not that your commercial M28 machine has heat exchangers. This means the BREWING water passes through the boiler,  but NOT into and out of the boiler water. The brew water is INSIDE separate piping called heat exchangers. The steam and stale boiling water in the boiler, which is so to speak "wrapped around" the heat exchanger pipes, causes the fresh "cool" water inside the heat exchanger pipe to heat up...ergo "heat exchangers". This water inside the heat exchangers comes direct from your mains water connection and is that which is pumped through the coffee grounds in the filter ,to produce espresso. Coffee is made with fresh water, the rest of the water/steam coming from your (anyones) commercial machine is stale.

      The purpose of the water (which becomes stale & de-oxigenated) in the boiler is to create steam, and to cause the exchange of heat into the fresh water coming through the heat exchangers. So there are 2 separate water systems happening inside the boiler, and they do not mix.

      Ergo, the explanation a couple of posts up re the separate flushing of boiler water and brew water in commercial machines.

      ***************

      Rich,

      as has already been noted in earlier parts of this topic the backflushing of DOMESTIC machines fitted with group solenoids is a bone of contention, and it begs a more technical discussion of what backflushing actually does.

      So for others in the forum that are not familiar with what happens with backflushing, it goes something like this:

      Brewing water passes through the boiler, into the group (heating up the group along the way) and into the groups electrovalve. The electrovalve is nothing more than an electric tap and it does not allow the passage of water back through the group and the coffee grounds until it is energised when the operator pushes the brew button on the mahcine. When it is energised, the valve opens and allows brewing water to pass through the group and produce espresso.

      So far, all of this is clean water.

      When the operator is finished brewing and the brew button is pressed off, the in line water pump PRESSURE that was pushing clean water in the direction of the group handle / filter holder has the opportunity to take the path of least resistance, which is to flow backwards agains the spring tension of the now de energised electrovalve, and "exhaust" the pressure (from the group) backwards into the drip tray...and this way you can remove the group handle from the machine without having it "explode" or pop off and put a heap of extremely hot water on your hand/wrist!

      What all this means, is that every time you make coffee, you have a flow of clean water through the electrovalve and group, and at the end of each coffee brewing "cycle" you have a corresponding "exhaust" or "pressure relief" of brewed coffee back through the group and electrovalve.

      In real terms then, you are flushing clean water through the electrovalve and group every time you brew coffee, or simply flow or purge water through the group. If an operator removes and cleans the group shower at regular intervals, most (but not all) of the garbage that solidifies out of the wet coffee brew to clog up the system, is cleaned out.

      Whilst backflushng with (approved) coffee machine detergent cleans out the shower, water passage and electrovalve without the need to remove anything, its primary function in the maintenance of an espresso machine is to lessen the possibility of the electrovalve becoming CLOGGED up with oily deposits over time and ceasing to function, whereby the operator can end up with burns to hand and wrist when removing the group handle, from the lack of pressure relief at the end of each brew cycle....and ofcourse, it lessens the possibility of introducing "off flavours" into your brew from any deposits of oily crud that can build up over time.

      If you watch the pressure relief into the drip tray, you will see that clean water is relieved / exhausted even when you siomply flow water through the group...ie, you dont need to use a blind fiilter tpo get some clean water flowing back through the electrovalve... but of course if you wish to use detergent to backflush with, you have to use a blind filter!

      Neither Rancilio nor Gaggia provide a blind filter with their "electrovalve grouped" domestic machines...

      The never ending discussion, with many interpretations !!!

      Regardez,
      FC.
      PS again for the benefit forum readers perplexed by all this....if your domestic espresso machine is not fitted with a group electrovalve or solenoid valve (MOST domestics), all of this is academic as you can only backflush solenoid / electrovalve operated groups.

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      • #18
        Re: Back Flushing

        Originally posted by Javaphile link=1097923570/15#16 date=1103823557

        Hey FC,

        I guess Im unclear by what you mean by the above quote as my Cimbali M28 only has the one boiler and all water used on it goes through the boiler.  Including that used for pulling shots.

        Java "Flush baby, flush!" phile
        Hi Java,

        did you end up pulling your cimbali right down and removing the HX from the boiler? The water path will become pretty evident once you have the pieces in front of you. As FC said the boiler steam/water is used to heat the shot water in the HX. The interior of my hx was pretty grotty and Im glad I cleaned it out.

        Some machines have the hx welded to the boiler and if the hx is damaged by freezing or whatever you basically throw the machine away, the cimbali hx fortunately is a seperate part which can be easily removed and replaced.

        Owen Egan has a good visual diary of what can go wrong with a hx check it out at http://owenegan.com/pix/espresso/cimbuini

        Comment


        • #19
          Re: Back Flushing

          oooOOOOOOoooOOOoo <Lightening flashes and strikes Javaphile and the lightbulb over his head goes on> Ive been laboring under a false assumption! Ive been assumming that the HXs are being fed with boiler water! <MANY things suddenly start to make sense!> Thanks FC!!!

          Yes mauricem I did actually tear my Cimbali all the way down. And I do mean *all the way down. By the time I was done there was nothing left on the frame but the electrical harness. However, it was not being torn down trying to find some problem. Rather it was a complete tear-down, cleaning/descaling, and rebuilding. Starting with a working unit.

          This was my first ever espresso machine (Ive owned several small pump units that claimed the name but werent) and when I finally got it after 3 years of back and forth between its now former owner and myself the only problem that prevented it from being used (and which the previouos owner had been attempting to fix for those same 3 years) was a leak. A leak I diagnosed and fixed less than 5 minutes after my friend and I had lugged the monster in and dropped it on my kitchen counter. LOL

          After Id fixed its only problem I then decided to tear it all apart, clean it, and put it back together as good as new. I followed the water paths and while there were a couple of questionable areas I *thought* I had them all figured out until FC threw a wrench into that! Knowing now that the HXs are being supplied with fresh water rather than boiler water I now know that the valves work a bit different than I had assumed (based on boiler water being fed to the HXs).

          A couple of head itches have now been cured thanks to this info! Such as why the steamed milk would taste of stale water but not the espresso. And why the temp of the water coming out of the head could drop so much if you ran a lot through it. And like why there was that other valve there when it really didnt appear to be needed! Nice!

          Goes to show what happens when one makes ASSumptions!

          Java "*pets* his newly lit over-head lightbulb" phile
          Toys! I must have new toys!!!

          Comment

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