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Inconsistent Group head pressure - measuring with a gauge

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  • Dimal
    replied
    Yep, most threads on coffee hardware (not all pipe fittings per sè) is BSP but there are exceptions, for those companies who like to be different.
    I used a needle-valve on my pseudo Scace Device too. Rather than use the Group Handle though, I fitted all the necessary hardware on to a blind filter basket that I can then transfer from type of 58mm group design to another without hassle.

    Mal.

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  • Ted2013
    replied
    Decided to lash out and order a 3/8" ss needle valve and " T" from Aliexpress. Cost all up about $18. Probably take 2 - 3 months to get here but not in a hurry. The hardest parts (for me at least) was being sure the threads were BSP and not NPT. If I had been guessing I would have though Italian coffee machines would have used a metric thread but presumably BSP is used as a plumbing standard all through Europe.

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  • Ted2013
    replied
    Like to add something. The Brasilia Portofino which was made by Gino Rossi is a joy to work on. Undo one bolt release the clip at the back and the side panel comes off. Easy access to the pump and 5 minutes to unscrew the bypass valve. This after unplugging the machine and turning the mains water tap off.

    So sad G Rossi went broke. Not sure what went wrong there. Perhaps too much emphasis on manufacture rather than marketting.

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  • Ted2013
    replied
    Jackster

    I was wondering about that. As I also own a BFC machine with a vibrating pump think I will modify my pressure tester to incorporate a needle valve.

    Mal You were spot on about the Bypass Valve on the pump sticking a bit. Removed the valve - items 13-22 on the attached schematic and found some scale on one side near the o ring. Cleaned it up, replaced the o ring applied some tap grease and reassembled and is now working fine on both group heads
    Attached Files

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  • Jackster
    replied
    It's a bit harder to regulate like that, and I don't like to encourage a leak there if I don't have one.
    ​​​​​​

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  • Dimal
    commented on 's reply
    Sounds like a good plan Ted...
    The pump itself is probably quite Ok, just the Bypass Valve assembly needs a tear-down, clean (maybe a new spring) and readjusting afterwards.

  • Ted2013
    replied
    Yes I think that is right. Some of the articles I have read suggest loosening the thread on the connector between the gauge and the PF to get about the 30 ml in 30 sec instead of the needle valve. Also after reading don't think it is that critical for a rotary pump. Also wondered if you could get the same effect by allowing a slow leak between the PF and the GH (ie not clamping in tight).

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  • Jackster
    replied
    For a needle valve, my pressure gauge threads leak a little. I figure that is like a needle valve.

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  • Ted2013
    replied
    Mal

    Had another go at it. Now think your original advice was spot on - "Could be the Bypass Valve on the pump sticking a bit in a random way"

    Found for a while that the adjustment screw was not responding well at all even using the pressure gauge on the machine. Ended up screwing it all the way down and back out a few times without getting much of a response and thought maybe I might need a new pump. Then suddenly the pressure on the machine gauge went high. After fiddling around a bit I was able to get a good reading both on the machine gauge and the PF gauge.

    Looks as if I will have to remove the pump and give it a good clean. It had not been adjusted since got the machine operational about 7 years ago.

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  • Ted2013
    replied
    Mal Did some more research on HB. One thought is that the pressure gauge almost certainly has no temperature compensation and is warming up while I was doing the measurements which could explain the variation in the readings I was getting. Will try again letting the PF cool to ambient temp between readings.

    The HB guys agree the needle valve does not make much difference with a rotary pump. One guy found a difference of 0.5 bar with adjusted valve (30 ml water in 30 seconds) vs. closed.

    Apparently the needle valve is more critical with vibrating pumps.

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  • Dimal
    commented on 's reply
    Ah Ok...
    Fair enough Ted. Worth a try.

  • Ted2013
    replied
    Mal Thanks You have given me another investigation project when time permits. Checked the hydraulic diagram for the machine. It does not seem to have separate pressure relief valves for each circuit In the meanwhile think I will just set the pressure a tad higher say 10 bar on GH1 which is the one I use mostly and see how the brew goes
    Attached Files

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  • Dimal
    replied
    Apart from the GH Pressure reading a little higher, the lack of a Needle Valve shouldn't matter re: consistency...
    Could be the Bypass Valve on the pump sticking a bit in a random way, or perhaps the Pressure Relief Valve(s) for each group circuit.
    Might have to do a bit of disassembly on the valves to make sure all is good...

    Mal.

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  • Ted2013
    replied
    Done some more reading about this and I discovered perhaps I should modify my tester so it includes a T piece and a needle valve so I can bleed off about 30 ml in 30s during the test equivalent to what is happening during a brew. Does that make sense? The gauge I am using is an Orman and is currently just connected to the bottom of the PF via a couple of brass fittings.

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  • Ted2013
    started a topic Inconsistent Group head pressure - measuring with a gauge

    Inconsistent Group head pressure - measuring with a gauge

    I finally got a pressure gauge from CP and constructed a Group Head pressure tester using an old portafilter. Tested it out on my old (1997) Brasilia Portofino 2 Group. Was able to easily adjust the pressure by turning the screw on the top of the acorn on the Procon rotary pump. As expected turning clockwise increased the brew pressure at the group head and I was able to get pressures varying between about 6 bar and 11 bar.

    What is puzzling me is that I had trouble getting consistent readings. I would adjust one GH to 9 bar and then go to the other GH and get an inconsistent reading. I even had trouble getting consistent readings at one GH. Tried two ways - adjusting the screw while pump was operating and adjusting the screw before switching the pump on (pressing the brew button).

    The GH seals seemed fine and were not leaking.

    Has anyone got any ideas on what might be happening?

    TIA
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