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  • Flow seems low

    The machine is an Expobar dual boiler I recently picked up. It has been disassembled cleaned, reassembled with new gasket and pressure adjusted to 9 bar at the group with a pressure gauge fixed to the porterfilter.
    What I have found is that the flow seems to be low, a 20 sec collection of water from the unrestricted group is 100ml. Which is about 5ml per second.
    I find the shots are taking about 10 seconds for first drips and finishing about 25-30 seconds depending on the beans.
    Is this flow low?
    What is the general unrestricted flow rate from a machine set to 9 bar?

    I have checked the little jet/nozzle in the E 61 group and it is not clogged nor is the filter screen.

  • #2
    This sounds ok for the shots.
    Assuming that it is an E61 group, did you remove the mushroom Upper part of the group and clean/inspect for lime scale?
    What is your water flow like from the hot water wand and steam wand?

    Comment


    • #3
      I might be missing something ... try grinding a smidgen coarser?

      Comment


      • Barry O'Speedwagon
        Barry O'Speedwagon commented
        Editing a comment
        I think that the op is saying that without a portafilter locked in, only 100ml are produced in 20 seconds of having the switch on.

      • tompoland
        tompoland commented
        Editing a comment
        Ah .. sorry, rewind, delete, take foot out of mouth. Tx BOS.

      • Rodels
        Rodels commented
        Editing a comment
        Yes Barry that is correct. Since my OP I have read that 500ml is a good volume for 1 minute collection, which equates to 8.3333'ml a second.

    • #4
      First thing I'd check is the plumbing from the water tank to the pump.

      I'm assuming the check valves on the pump are OK because you are making pressure. Next most likely cause is inlet flow restriction: pumps perform poorly when the NPSH climbs (NPSH = negative pressure suction head, eg the suction pressure the pump has to develop to maintain flow.*)

      Since the pump cannot operate with NPSH greater than 10 metres (1 Bar) but will operate with output pressure up to 15 Bar, it is much more sensitive to flow restriction on the inlet side.


      * It is normally stated as a head since a common cause of pump problems is having the pump inlet too far above the source. No water pump can operate at more than 10 metres NPSH. This is because the motive force on the inlet side is the difference between atmospheric pressure and the absolute pump inlet pressure and there cannot be an absolute pressure less than zero. If atmospheric pressure is assumed to be 1 bar, approximately the pressure exerted by a 10 metre high column of water, maximal NPSH is 10 metres.
      Last edited by Lyrebird; 6 November 2022, 08:46 PM.

      Comment


      • amberale
        amberale commented
        Editing a comment
        Sort of why I asked about the flow from the other boiler and the mushroom.
        Possible scale build up in a second/third hand machine.

    • #5
      Originally posted by amberale View Post
      This sounds ok for the shots.
      Assuming that it is an E61 group, did you remove the mushroom Upper part of the group and clean/inspect for lime scale?
      What is your water flow like from the hot water wand and steam wand?
      Descaled and inspected.
      Water and steam wands are fine.

      Comment


      • roosterben
        roosterben commented
        Editing a comment
        Have you physically checked the outlet from the boiler to the group head is clean/clear of scale? I have had machines that I have descaled that have had calcium deposits blocking these outlets.

        Also is the machine plumbed rotary pump or the tank vibration pump model?

        If it is the vibration pump model you pump might be shot, they are cheap and easy to replace.

      • Rodels
        Rodels commented
        Editing a comment
        Yes the whole machine was stripped, cleaned and rebuilt with new gaskets and parts where needed.


        I am thinking I might just remove the hose after the OPV and see what the flow is like there.

    • #6
      Today I removed the tube after the air bleed and OPV assembly which are attached to the pump and measured the volume of a 30 second flow. The result was a little shy of 250ml (248ml there abouts) and when assembled and measured at the group the voulume was 180ml. After removing the restrictor in the group I was able to get about 222ml.
      Not sure if a new pump would have any impact on the tests. It works, operates with back pressure.

      However after writing the previous I returned to the machine after it had fully warmed up and did another test only to find I had a good stream of water out of the group for about ten seconds and then it ran out and water began to exit in burst after that. Reinserted the restrictor and it is back to normal and getting about 170ml out.
      Last edited by Rodels; 27 December 2022, 11:52 AM.

      Comment


      • #7
        Have you made coffee on it and if so did you enjoy it?

        Comment


        • #8
          I don't know heaps about Expobar machines, but I'm sure I remember reading somewhere that they use a proprietary group head that gives a sort of automatic pre-infusion. Is that right? Or can you put the lever in the half way position for pre-infusion? I'm assuming you're testing the flow without a portafilter in place and the lever in the full open position. If I'm correct about the mechanics of the group head then 100ml in 20 seconds is pretty much perfect isn't it? If everything else is working fine, you're reaching full pressure and the coffee you're producing is good then I think it's ok and you might be on a bit of a wild goose chase for no reason. Hopefully a tech jumps in here that has a bit more knowledge of Expobar machines. In the meantime I'd just use the machine as is.

          Comment


          • Ronin
            Ronin commented
            Editing a comment
            Expobar use a standard E61 group. Nothing you can’t do on any other E61 machine with lever.
            Flow looks about right, same as my current personal machine. That’s why I asked if there has been coffee made on the machine

          • LeroyC
            LeroyC commented
            Editing a comment
            Ah ok. It must be their non-e61 machines that have the proprietary group heads with automatic pre-infusion. Either way it sounds like the flow is about right.

        • #9
          Originally posted by Ronin View Post
          Have you made coffee on it and if so did you enjoy it?
          Yes and not really.

          I just purchased a new machine, not an Expobar. I did a flow test on it last weekend and per minute I was collecting about 600-640ml which is much better and pulling nice shots.

          Comment

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