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Inexpensive home made portafilter pressure gauge

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  • Inexpensive home made portafilter pressure gauge

    Recently changed the OPV valve on my V2 Silvia. Seemed to operating at a higher than normal pressure and given the propensity for the Silvia's to be wound up a bit high out of the box I rigged up an inexpensive portafilter pressure gauge and made the appropriate OPV adjustment. It's now bang on 9 Bar (900 ATM) and pulling much better shots.

    For those interested, it's a liquid filled Holman pressure gauge from Bunnings for $15.90 and a brass reducer from 'Total Eden' for $6.00.





  • #2
    There is now a guy out of Spain I think on ebay, who sells one for about $35, which I decided was worth while vs making my own, only catch for me was it was not till I was trying it out today, I realized Lelit grind out two slots in the group, making my purchase now somewhat useless.

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    • #3
      Nice job Sam.

      Two questions for you:

      - is there a hole to allow flow anywhere? (If not, your flowing group pressure may not be what you think it is)
      - What is the pressure rating of your brass fitting?

      Comment


      • #4
        Good headup Sam

        BTW do you recall the thread sizes on the reducer?

        Originally posted by MrJack View Post
        Nice job Sam.

        Two questions for you:

        - is there a hole to allow flow anywhere? (If not, your flowing group pressure may not be what you think it is)
        the flowing group pressure is going to be a reducing pressure through the system from the set value of the OPV to atmosphere at the exit of the Group head regardless.
        By gagging the group head you will see pretty close to the OPVs adjusted value as the pressure would rise throughout the system to very close to the static pressure of the OPV (unless there is a leak somewhere).

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        • #5
          Nice cheap gauge for sure but for this purpose the guage really needs to go up to ~16bar. 10bar may have been ok in this case because the machine was already set to roughly 10bar but many will be running much higher pressure (up to aprrox 17bar) and will destroy the gauge pretty quickly. Sorry to put a damper on things.

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          • #6
            Originally posted by koshari View Post
            Good headup Sam

            BTW do you recall the thread sizes on the reducer?



            the flowing group pressure is going to be a reducing pressure through the system from the set value of the OPV to atmosphere at the exit of the Group head regardless.
            By gagging the group head you will see pretty close to the OPVs adjusted value as the pressure would rise throughout the system to very close to the static pressure of the OPV (unless there is a leak somewhere).
            A few thing to consider:
            A) you're not interested in the OPV setpoint, you're interested in the group head pressure
            B) When flowing, there is pressure drop between the OPV and the group, so the group pressure will be slightly lower than the OPV setpoint.
            C) Dead heading the group means that all the flow is directed to the OPV - this may increase the pressure at the OPV.


            The effect is small, but real.
            Last edited by MrJack; 8 December 2014, 09:40 PM.

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            • #7
              Sam - do you recall the thread sizes on the reducer?



              the flowing group pressure is going to be a reducing pressure through the system from the set value of the OPV to atmosphere at the exit of the Group head regardless.
              By gagging the group head you will see pretty close to the OPVs adjusted value as the pressure would rise throughout the system to very close to the static pressure of the OPV (unless there is a leak somewhere).[/QUOTE]

              So given that Sam progresses to STAGE 2 group pressure gauge - IF he adds a 'T' piece thread adapter ( in place of the female / male thread adapter there now) - with an adjustable tap to allow adjustable flow up to 30ml in say 30sec
              The question is would this more closely replicate group head pressure as measured as per a normal shot situation?

              PS anyone care to comment who has seen / used Greg Pullmans 'gauge on the road' and how itis setup?

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              • #8
                Greg's gauge is pretty much set up as you've described, with what appears to be a bespoke needle valve downstream of the pressure gauge connection.

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                • #9
                  I was of the understanding that the no flow or 'static' pressure should be 10bar as this generally indicates a dynamic (with flow) pressure of 9bar. Also the problem with a standard gauge from Bunnings is that it's temperature range probably only goes as high as 50-60degC. So when you are testing water that is obviously hotter than this you can't guarantee an accurate reading. These are all the reasons that stopped me doing the same thing and had me searching the net for a suitable gauge. I actually found one on the bay, purpose built for the task, sold by Edesia Espresso in the UK. I've tested it once and it seems to work well.

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                  • #10
                    Originally posted by LeroyC View Post
                    I was of the understanding that the no flow or 'static' pressure should be 10bar as this generally indicates a dynamic (with flow) pressure of 9bar. Also the problem with a standard gauge from Bunnings is that it's temperature range probably only goes as high as 50-60degC. So when you are testing water that is obviously hotter than this you can't guarantee an accurate reading. These are all the reasons that stopped me doing the same thing and had me searching the net for a suitable gauge. I actually found one on the bay, purpose built for the task, sold by Edesia Espresso in the UK. I've tested it once and it seems to work well.

                    [ATTACH]9537[/ATTACH]
                    Leroy. All guages are calibrated at 20 degrees c.

                    Cant see it being a problem at 100 degree c. At work we put pressuse gusges on piping with much greater temperature. Besides with a small length of pipe/hose the there is little chance the actual guage will even get warm.
                    Last edited by koshari; 10 May 2015, 08:07 AM. Reason: Additional

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                    • #11
                      Originally posted by koshari View Post
                      Leroy. All guages are calibrated at 20 degrees c.

                      Cant see it being a problem at 100 degree c. At work we put pressuse gusges on piping with much greater temperature. Besides with a small length of pipe/hose the there is little chance the actual guage will even get warm.
                      Interesting. I looked at getting a gauge from Horshams as we can get them through work and they're a high quality gauge. But they said the operating temp range only went up to 60degC. They said it would probably work fine well above that, but they couldn't guarantee its accuracy. I guess they just have to say that for a bit of risk aversion.

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                      • #12
                        You aren't going to pull shots through it nor leave it connected to the machine for long periods so it's not going to reach brew temp.

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                        • #13
                          Yeah I realise that, I don't think they're worried about the gauge getting hot. I think it's pretty standard for industrial instruments to have an operating range and for these gauges that are calibrated at 20degC their operating range doesn't extend beyond 50 or 60deg. I guess as the density of the product that's being tested changes this could affect the reading given by the gauge. It's probably minimal, but I wouldn't know. Maybe there's an engineer here that can explain it better.

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                          • #14
                            Originally posted by LeroyC View Post
                            I was of the understanding that the no flow or 'static' pressure should be 10bar as this generally indicates a dynamic (with flow) pressure of 9bar.
                            Maybe, maybe not. This will depend on the OPV and the piping between the pump and the group. It's possible that machine designers typically aim for a pressure drop of 1 bar at normal flowing conditions, but if you're going to the effort of building a measurement assembly, why rely on such an assumption?

                            I did test this with Greg's gauge, but I forget what the difference was on my machine.


                            With respect to temperature, I suspect that the 60°C limit has more to do with the gauge itself (and any fluid within) than the fluid being measured.

                            There could be other reasons for such limits (although most a likely to be more relevant in industry than at home), such as material issues with soft components or corrosion.

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                            • #15
                              Similar to MrJack, it does make a bit of a difference but I can't recall the amount. It wasn't enormous, I think it might have been a bar or maybe a bit less, not a lot but it's there which is why I put the bleed mechanism into mine. I always think being able to check the pressure at the group is the most important factor, my Giotto has a boiler and pump pressure gauge but invariably the pump pressure gauge doesn't correlate exactly with what's at the group.

                              I've got one of those Holman gauges at home for checking mains pressure but they do only go up to 10 bar. I bought my gauge several years ago now but made sure I got one which went up to 16 bar (heck if it's pushing out more than that you shouldn't be drinking it! ). IIRC the whole assembly cost around $100 (the gauge itself was about $60 but it was a fairly good quality one), and the fittings, bleed mechanism etc added the rest. It's just about to come back to me for a check-up but last time I got it back it was still running fine.
                              Last edited by gregpullman; 22 May 2015, 11:25 AM.

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