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Thread: Pressure measuring portafilter

  1. #1
    Senior Member
    Join Date
    Apr 2005

    Pressure measuring portafilter

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Necessity is the mother of invention.... okay this isny my idea, but its my implementation. A trip to Tony Powell Hose Supplies and $40 later and I have a pressure measuring portafilter with a (supposed) needle valve to regulate the flow.

    This is only the MkI model. I might go to attaching the gauge via a flexible teflon pressure line. However, it worked and has helped me try to understand how my machine is operating. The one caveat is that the needle valve doesnt seem to be a needle valve, but some other valve that seals and can be cajoled into letting the slightest dribble through before exploding and completely depressurizing the portafilter and making me take a trip to the laundry to wash my soiled undies :o. Nevertheless, the valve worked long enough to get some insight into the operation of the machine. It was also much cheaper than a purposely built pressure sensing portafilter and can be easily converted back to operation as a conventional PF. Nice. The needle valve (if it worked) is also VERY useful and not an option on the purpose built ones.

    Heres a pic with all the details including how it attaches to the machine.

    I used yellow teflon tape for all the seals. It works brilliantly. Much better than white.



    BTW: 100 kPa = 1 bar, so the gauge will read upto 16 bar.

  2. #2
    Senior Member
    Join Date
    May 2005

    Re: Pressure measuring portafilter


    Interesting stuff. Necessity can be a mother, for sure.

    What did you learn about the pressure profile on the BZ-35?


  3. #3
    Mal Dimal's Avatar
    Join Date
    Oct 2004
    Warwick, QLD

    Re: Pressure measuring portafilter

    Yeah, good one Sparky [smiley=thumbsup.gif],

    Been thinking of doing something along similar lines but using my old set of refrigeration test gauges. This gives me enough inspiration to get off my bum and do something.

    Should have no trouble now tailoring any machine to operate at ideal Specs, what with temp profiling and now pressure monitoring and adjustment (where thats possible of course). Looking forward to your next round of test results :).....


  4. #4
    Senior Member
    Join Date
    Dec 2004

    Re: Pressure measuring portafilter

    Nice one Mark.

    I built something similar not long ago. Mine has got more of a horse shoe shape going on. The tap (only one I found at about 4 plumbing supplies places) has a ball valve (?). As you turn the tap the a ball shape closes across the opening. It is capable of mimicking the release of espresso in terms of volume of liquid over a given time. One thing Im not sure of though, is whether to allow 30 or 60mls to escape over a 30 second period?
    Ive read that the pressure read against a blind filter is approx 1 bar above actual shot pulling pressure.
    I ended up getting a dry gauge but with a snubber. There is a little flutter but nothing annoying.
    Ive tried my home made gauge on a commercial machine with a built in brew pressure gauge and they both show the same pressure so Im assuming it is working properly.
    The pressure on my machine was in the 11.5 bar region, I wound it back to approx 9.5. Hard to state categorically, but shots since survive ristretto pours in much better shape and are generally less harsh. Could be just imagining it though *:)


  5. #5
    Senior Member robusto's Avatar
    Join Date
    Feb 2005

    Re: Pressure measuring portafilter

    Well done, Sparky, and a very neat, professional job. (Maybe you can chrome-plate everything for even more spectacular looks).

    You mention that you needed to know, hence your apparatus. What have you learned? Any surprises?


  6. #6
    Senior Member
    Join Date
    Apr 2005

    Re: Pressure measuring portafilter

    Behmor Brazen - $249 - Free Freight
    Ive used the pressure PF to set the OPV to open at 10.5 bar. As the needle valve isnt working, thats the choked pressure. It was nice to be able to watch the pressure rise as you turn the OPV screw. It went from 4 bar to 11 and I settled on 10.5.

    This should only affect the performance for ristrettos and singles.

    When I got the machine, the OPV was set to 16 bar (ie the max pump pressure).

    The needle valve looks to have an o-ring in it, which shouldnt be there. If I can pull it apart I might be able to fix it. I guess thats what you get when you buy cheap....

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