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OPV article - interesting read

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  • OPV article - interesting read

    Ive been stung by the Tinker Bug and have been searching around for information on OPVs (Over Pressure Valves) with the view of tinkering with my Saeco Via Venezia. Main purpose is to investigate cheap options to gain more consistency in brewing starting with brew pressure by adding an OPV & pressure gauge.
    I came across this article on OPVs which I thought worth sharing. This is all part of the search for a vaccine before I contract that dreaded upgradeitis which seems to be rampant and an ever present threat!  :P :P :P

    http://myweb.tiscali.co.uk/coffeetim.../OPV_Valve.pdf

    Being fairly new to the sport I soon discovered huge variations in taste especially when the brew temperature is varied. Currently the only way to do this is temperature surfing by varying the length of time before I brew from when the brew light comes on (hence boiler slowly cools before switching heating element back on). Ive gone from a grind setting of 9 before getting bitter coffee down to a 5 by brewing at a slightly lower temperature and am still experimenting. A cheap temperature gauge for the boiler is also on the list.
    As grind and tamping pressure consistency seem to dictate brew pressure without an OPV in the machine, I thought the easy way to knock out this variable might be with an OPV?
    This should ensure consistant 9BAR brew pressure instead of up to 15BAR if all wasnt right with gring / tamping etc. If this isnt cost effective, lots of extra attention to grind and tamping pressure will definetly be required! 

  • #2
    Re: OPV article - interesting read

    Well something to keep in mind perhaps is that if you pack the coffee tighter, or increase the quantity of coffee, you should need a higher pressure to maintain the same flow rate. Youre quite correct that after 9 bar is reached, the OPV means you are at constant extraction pressure. However, the flow rate will still vary depending on your grind, tamp, and also the dose (which is highly important!). So the same operator variables will produce different coffee outcomes and the coffee will still have a significant dependency on them- but I guess the point is that most of the results would be better with the OPV than without

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    • #3
      which one fits your Seaco?

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      • #4
        Originally posted by C-man View Post
        which one fits your Seaco?
        To be honest I haven't pursued this modification since I realised the Saeco Via Venezia comes with a mechanical Pressure Release Valve of its own (see link below) between the pump and boiler which empties water back into the reservoir once a set pressure is reached in the boiler.

        http://www.espressocare.com/Qstore/Q...+Release+Valve

        I suppose this works the same as an OPV?

        Haven't pursued it further as I'm comfortable with the results I'm getting now.

        In case you're interested the link below has interesting information as well as good pictures that show the innards of the Via Venezia and how to disassemble it.

        Its for the USA version which is called the 'Starbucks Barista' but the same machine except for being 120V and also has a different steam wand as far as I can tell.

        Starbucks Barista Repair Manual - iFixit

        The comments from papagoose above cover other variables that come into play as well.

        Last edited by CafeLotta; 8 October 2012, 08:50 PM. Reason: added link for PRV

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        • #5
          It would but what is it set at is the question, does it have an adjustment on it?

          My OPV valve and gauge came in the mail today, I guess I will hook it up over the weekend.

          I read on CG where guys are using light dimmers or fan controllers to slow down the pump to lower the pressure during the extraction with good success.

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          • #6
            Originally posted by C-man View Post
            It would but what is it set at is the question, does it have an adjustment on it?
            I don't know for sure as I haven't tried it myself but I have read somewhere that by screwing the barb fitting end of the Saeco Via Venezia pressure release valve in or out slightly, the set pressure can be varied.

            Might be some sort of spring in there that has its tension increased or decreased by doing this. Let us know if you do try it!

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            • #7
              Originally posted by CafeLotta View Post
              I don't know for sure as I haven't tried it myself but I have read somewhere that by screwing the barb fitting end of the Saeco Via Venezia pressure release valve in or out slightly, the set pressure can be varied.
              Should have also added that if anyone tries this you need to be sure the pressure release valve doesn't start to leak and as usual its at your own risk.

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              • #8
                I am going for it right now, wish me luck.

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                • #9
                  Click image for larger version

Name:	Sunbeam mod 002 (Large).jpg
Views:	2
Size:	70.6 KB
ID:	733143came out pretty good, no leaks first up just using Teflon tape on all threads (plenty)

                  plumbing was easy, just a real bitch drilling through the Stainless steel casing

                  getting great shots now and the whole machine is much quieter,
                  Attached Files

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                  • #10
                    Originally posted by C-man View Post
                    [ATTACH=CONFIG]1109[/ATTACH]came out pretty good, no leaks first up just using Teflon tape on all threads (plenty)

                    plumbing was easy, just a real bitch drilling through the Stainless steel casing

                    getting great shots now and the whole machine is much quieter,
                    Good to hear you're having success. What brand were the items you actualy purchased?

                    For some reason I was under the impression that you were looking at buying a 2nd hand Via Venezia. I didn't realise you were going to mod the Sunbeam!

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                    • #11
                      If you look at the thread close to this by Karl I did pretty much what he did.

                      called sunbeam OPV mod getting good shots now

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