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Home made adjustable OPV for Gaggia Classic Pro

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  • Home made adjustable OPV for Gaggia Classic Pro

    Having bought a Gaggia Classic Pro with little more thought than "AVE showed one and it didn't have any electronics in it, and there's a lot of hype about it" I'm now finding all the non-hyped things like the big pressure from the factory.

    So the first thing was to measure the pressure ex-factory. I looked on Bunnings website and didn't find the 3/8 to 1/4 female to female adapter that MedaGalax found, so rather than spending about $5 on that I spent $15 on 2 cheap taps (one of which is not fit for purpose) and a few hours making one.

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    That showed me the factory setting was 13.25 bar.

    I measured the spring so I knew roughly what I wanted and couldn't find it locally and didn't want to spend a lot of south pacific pesos getting one from the usual suspects.

    So I made an adjustable bit for the OPV to allow the spring compression to be backed off a bit.

    Here's the general idea.

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    Here is the prototype (with the factory spring), which will probably be in place forever. I should have made it from brass hex, but I cut the test M10x1 threads on a short end of 12.7mm round and the 2nd one was ok so I just kept going with that material! Later on I did regret this.

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    Here it is in place.

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    And at 9 bar.

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    Sorry all the photos are dodgy. I've just started using a Mac and don't have the programs I'm used to for cropping and resizing etc on Windows.


    I made the female part of the adjustment spring too shallow - it looked ok in CAD but by the time you take the tap lead in etc into account it wasn't really enough.

    So a revision would be better and easier to use, but this one is working and not leaking so I think I'll leave it.

    I can't say whether the coffee is any good, but it's better than that from at least 2 cafes I go to so that's something!

    No grinder yet. I was using supermarket ground coffee... you can imagine how that went at 13.25 bar - the water just rushed through it. Now I have some espresso ground at a local roaster and that's much better.
    Attached Files

  • #2
    Well done Dajt encourage you to not stop there.....I'm thinking your just the guy with the competency you've shown in this job thats there's likely an adjustable flow control valve amongst other things in your espresso toolkit.... lurking !

    Comment


    • #3
      Thanks EspressoAdventurer!

      What is an adjustable flow control? Is that controlling the pump with a dimmer or a microcontroller?

      I have the bits for PID control on the way, based on a blog post. I'm pretty worried about the SSR now. Having again dived in before doing any research I now learn most SSRs are fakes and given the one I bought cost 10x less than a similarly rated one from a reputable supplier... my hopes are not high. Still, unless it is a really dodgy one I think it will only be working at about 25% capacity so might survive.

      I have to say I'm stumped why the magic spring is so difficult to find. A stainless spring, 0.75 dia wire, 7.0mm outside dia, about 24mm long, a few less coils than stock shouldn't be unobtanium locally.

      I'm planning a better version of the adjustable OPV, allowing the use of the original brass piece so only needing the spacer piece and perhaps a little slug to fit inside to get the spring in just the right position. The only reason I couldn't do it this time was because I don't have a M10x1 tap and didn't want to buy one just to find the idea didn't work.

      Then I could consider a custom steam valve handle if I can figure out how to attach to the D shaft without a set screw - mine would be on top and visible.

      Mounting a pressure gauge permanently would be cool too. I think I'd do it like the one from the UK with a little outtake between the boiler and the 3 way solenoid rather than teeing off the hose going into the boiler. That doesn't seem the right place to take the pressure although I don't know enough about the flow through the boiler (or about measuring pressure) to know.

      It would be good to get a broken machine to really get to grips with all the dimensions and parts without taking my new one to bits!

      Comment


      • #4
        Dajt Im a mere mechanic...so no elect wiz.
        But there are some real high level electrical types here whom Im sure can offer you sound advise.

        The best of those even liked your post #3 !

        I dont have a Gaggia u/f but do like a good ...pimp my pumper thread.

        As for the shot pressure gauge....make sure you run a few loops of the 1/4" pipe in a 'circle' with the bottom of the loop below the level / pos'n of the gauge as this will assist in keeping moisture out of the gauge long term.

        Keep the motivation up...and enjoy your espresso.
        GL

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        • #5
          The 40A "Inkbird" units listed on Amazon or eBay would be Ok, especially at the rated load of the Classic's boiler elements...

          Mal.

          Comment


          • #6
            Thanks Mal, I'll see how I go.

            While waiting for the fire hazards to arrive I bought some aluminimum to make a new steam wand knob. Aluminium is not cheap so I only bought enough to make 2!

            It was disappointing to use a set screw to hold it on but I could not find inserts to fit a D-shaft anywhere for sale and I couldn't be bothered machining the necessary shapes so here we are. I looked at all the appliance knobs in my kitchen and they're the same as the standard GCP knob with the D-shaft shape moulded in and a piece of spring steel to provide some force on the shaft.

            I'm happy enough with it but I was envisioning a chunkier knurl. This was as good as my knurling tool could do, it was cranked down pretty hard.

            It feels much better than the standard knob but it might get damned hot because there's no insulation between the steam valve spindle and the aluminium body. If it gets too hot I'll hollow it out and stuff some wood or something in there.

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            • Lyrebird
              Lyrebird commented
              Editing a comment
              Hollowing it out and adding wood will make very little difference: the aluminium will still act as a thermal bridge.

              Thermal conductivity and electrical conductivity in metals are mediated by the same mechanism, the presence of free electrons, so they act in much the same manner. This is why metals (generally) conduct both electricity and heat well and why the best metals for conducting electricity (silver, copper and aluminium) are also the best metals for conducting heat.

              It isn't hard to imagine how well your piece of aluminium will conduct electricity before and after hollowing it out: in both cases it will conduct very well. The same will apply to thermal conductivity. Just like in electrical conductivity, if you want to prevent heat being conducted you need to break the path, so you would need for there to be no contact between the outside of the aluminium knob and the shaft and for the material interposed to be a good insulator.

              Unfortunately the analogy breaks down here as non-metals conduct heat via a different mechanism (lattice vibrations called phonons rather than actual electrons) so a good electrical insulator is not necessarily a good thermal insulator. The ultimate example is diamond: a very good electrical insulator and the best naturally occurring heat conductor known.
              Last edited by Lyrebird; 22 December 2022, 12:03 AM.

          • #7
            Dajt I put an alloy knob on my Lelit. It was too hot to comfortably use.

            Comment


            • #8
              Thanks for the info!

              I guess a diamond sleeve will be necessary

              I'll give the wood a go anyway because I've spent the time and money to make this and don't want to just throw it away without trying a few things. The set-screw might be an easy path for the heat to get through too. I could also use a little wood plug under the set-screw.

              Comment


              • #9
                Lyrebird has called it. Today I finally found the pieces of PTFE rod I had stored in a safe place and tried them. First up 10.5mm rod, leaving 2mm all around the steam valve spindle. Didn't seem to make much if any difference.

                Then I hollowed the knob out to a 22mm bore and used a different, I think harder, plastic. It's better and after 10 mins I can still use it with my bare hand but I wouldn't hold on to it too long. I doubt anyone sensible would use it like it is.

                I'll leave it and see how I go. No-one else in the house uses the machine anyway.

                My PID, thermocouple, and 'Fotek' [sic] SSR have arrived. I need to purchase some of those piggyback connectors and mains thickness wires before I can get into it. The 'Fotek' is marked 25 amps and does not fill me with confidence!

                I was wondering why people would put thermal paste in contact with their water until I figured it must be a blind bush in the boiler. So we're really measuring the boiler shell temperature. Is the water the same temperature?

                Comment


                • Dimal
                  Dimal commented
                  Editing a comment
                  Some info here about the preponderance of fakes...
                  https://protosupplies.com/inferior-c...on-the-market/

                • dajt
                  dajt commented
                  Editing a comment
                  Thanks Dimal. I am now certain mine is fake, as if the price being 1/10 of anything from a reputable supplier didn't say it all.

                  Not sure what to do now. If it explodes it could damage my machine or cause a fire. If it fails closed it will do in the thermal fuse and I don't know how easy that is to replace.

                  Seems like a dodgy prospect TBH!

                • Lyrebird
                  Lyrebird commented
                  Editing a comment
                  You can get decent 25A SSRs from the likes of RS and Element14 for about $30.

              • #10
                I have used the steam wand knob bare handed the last few days and it's fine. It's hot, but it's not so bad you flinch away from it! You certainly couldn't sell it as-is.

                Cleaning the showerhead I see about 4 holes were not drilled (punched?) through from the factory. A number 80 drill fits through the holes, but I am not going to try to drill the blind ones. That drill is very fine and would break if I tried. So poor quality from the factory there. A nice sharp edge on the central screw hole where it was punched through too!

                I have just watched a WLL video about pressure and it looks like a waste of time installing a pressure gauge anywhere in the water circuit so I'm not going to bother with that.

                That video made the interesting point that you don't want 9 bar showing on a static pressure gauge on the PF either. They recommend adjusting for 10 bar on a static PF gauge so I might do that. Then Hoffman recommends 9 bar on the static gauge to get 8 bar going through the coffee! I'd betting I'll taste no difference whatever the setting from 10 to 8
                Last edited by dajt; 30 December 2022, 02:13 PM.

                Comment


                • #11
                  I spoke to an electrician friend yesterday about PIDs. He has added PID control to his camping fridge because he figured out temperature control on them is essentially a duty cycle selection, not a temperature selection.

                  His point was that in addition to dodgy SSRs, an SSR can dissipate a large amount of heat due to voltage loss x current flow and he reckons just using the coffee machine body as a heat sink is a pretty sketchy proposition.

                  Almost everyone is getting away with it, perhaps because the SSR isn't on for very long at a time.

                  But to do it 'properly' you'd have to get a decent heatsink, a decent SSR, and the SSR would then be mounted outside the machine because it won't fit inside with the heat sink.

                  I reckon that would add up to at least $100 and a tricky installation trying to make it safe, such as insulating the heater wires so no-one gets electrocuted. Maybe another day!

                  I'm happy enough with the machine as it is now. It seems to be making good enough coffee, although I'd hardly know!

                  Does anyone know how the pump is controlled? If there is a coil switching on and off, what controls that switching?

                  Comment


                  • #12
                    I've used the fostek SSR clones for numerous diy pid and gaggiuino installs. Never had an issue.

                    ​​​​
                    As for how the pump is controlled. The brew rocker switch literally activates the pump and solenoid valve. Nothing sophisticated.




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