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  • ulka pump power reduction

    this is an idea for my frankensilvia, but how can I reduce the power output of an ulka pump? I don't know enough about them to know if they can be controlled like an AC or DC motor - do I need to reduce the frequency as well, or will a triac circuit (like a light dimmer circuit) work?

  • #2
    I believe they're basically a solenoid that cycles at AC mains frequency, phase angle dimming *might* do something but I'm a bit skeptical, only thing I've seen done to control an Ulka is pulsing the input power.

    Some form of Variable Frequency Drive might work but isn't exactly a simple prospect.

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    • #3
      they're only 48W though so maybe chopped DC through some IGBTs would still drive them (especially if they're a solenoid so that they don't need the sinusoidal pattern).

      I'm worried that pulsing the input power at macroscopic-time scales will just lead to pulsating pressure and the OPV flapping open and closed.

      what I'm thinking here is that if coffee is brewing at the magical 9 bars, the ulka is rated to pump 260cc/minute at that rate. that's good if you're making a super-lungo, but if I'm making a 30ml ristretto in 30 seconds, that means that 90ccs of water are being returned to the tank per shot, and that 120ccs of new water (at whatever temperature - presumably not much above room) is coming into the boiler during the shot. no wonder intra-shot stability isn't very good! if I can reduce the actual flow rate of the pump, so that a minimal amount is going out the OPV, then the intrashot stability will be much better (and also will be much easier for the PID to account for).

      I now have a new idea - a little jar inside the water tank. so that the first water that is taken up by the tank is OPV water. backflush before the shot to heat up the water in the jar, and so the water coming into the boiler should be a lot warmer than the rest of the tank.

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      • #4
        If I understand what you're saying correctly and if the layout is the same as the Gaggia Classic, don't bother.

        Is is the OPV not upstream of the boiler?

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        • #5
          what direction is upstream?

          I don't think the OPV is before the boiler, because OPV water is hot.

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          • #6
            Originally posted by Hildy View Post
            they're only 48W though so maybe chopped DC through some IGBTs would still drive them (especially if they're a solenoid so that they don't need the sinusoidal pattern).
            True, a bit simpler than a proper VFD, not sure how well it'd work though.

            Originally posted by Hildy View Post
            I'm worried that pulsing the input power at macroscopic-time scales will just lead to pulsating pressure and the OPV flapping open and closed.
            I'm kinda skeptical about this approach myself.

            Originally posted by Hildy View Post
            what I'm thinking here is that if coffee is brewing at the magical 9 bars, the ulka is rated to pump 260cc/minute at that rate. that's good if you're making a super-lungo, but if I'm making a 30ml ristretto in 30 seconds, that means that 90ccs of water are being returned to the tank per shot, and that 120ccs of new water (at whatever temperature - presumably not much above room) is coming into the boiler during the shot. no wonder intra-shot stability isn't very good! if I can reduce the actual flow rate of the pump, so that a minimal amount is going out the OPV, then the intrashot stability will be much better (and also will be much easier for the PID to account for).
            Huh? The only water to enter the boiler during the shot is the 30cc that displaces the 30cc for your shot, the rest of it never makes it into the boiler since it goes straight out the OPV bypass and back to the tank, certainly it'll leach a little heat away from the boiler in doing so but I don't imagine it would have a major impact, particularly given that there's 4.5kg of hot brass as ballast.

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            • #7
              Originally posted by Hildy View Post
              what direction is upstream?

              I don't think the OPV is before the boiler, because OPV water is hot.
              Before.

              Warm hot or 96°C hot?

              I think you will find the pump feeds the OPV, which discharges 9bar to the boiler and the remainder back into the tank. The first bit of discharge from the OPV will be hot because the OPV appears to be bolted to the boiler (and will therefore be hot until flushed with cold water during a shot).

              As for the OPV causing fluctuations in the output when sitting at ~9bar (or whatever), it won't. It's designed to gradually regulate pressure as required and is subject to constant spring-pressure, it's not actuated on/off.

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              • #8
                The OPV is physically attached to the boiler on the silvia so the water passing out the OPV does steal heat from the boiler, its not straight boiler water coming out though

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                • #9
                  The effect is minor though, and absolutely negligible next to the effect of the 1-2cc's/sec of cold water entering the boiler. during a pull.

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                  • #10
                    ok, so maybe it was a stupid idea. I still want to be able to reduce the pressure so that I can do pressure profiling.

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                    • #11
                      Not a stupid idea, dude, just won't work the way you thought it would.

                      Pressure profiling would be difficult, but I imagine you could do it with a gauged PF and manual adjustment of the steam valve to drop pressure on the fly.

                      Cutting pressure below 9bar (or whatever your OPV is set to) by underpowering the pump will cause pressure fluctuations as the vibration pump doesn't provide a steady/regulated pressure output - that's what the OPV is for and you'll be operating below the OPV's operating threshold.

                      And that's assuming that the pump could be run properly at reduced frequency or voltage, which I couldn't say one way or another.

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                      • #12
                        Originally posted by Hildy View Post
                        ok, so maybe it was a stupid idea. I still want to be able to reduce the pressure so that I can do pressure profiling.
                        Maybe not so stupid. It has been done. I recently saw an old post on another forum where a light dimmer switch was used to control power to a Gaggia Classic pump. On another forum the same mod was done on an old model Silvia. Apparently both worked OK.

                        One of them had also fitted a pressure gauge, and I think he was adjusting the pressure during the shot in an attempt to copy the pressure profile of a lever machine. Cant remember how successful that was.

                        I think one was on coffee geeks and the other was on the home barrister site, but I'm not sure. A search for "light - dimmer - gaggia - silvia - pump" might find them.

                        Cheers, deegee.

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                        • #13
                          Re: ulka pump power reduction

                          Could the OPV be discharging because the pump is oversized? That is to say, the design of the pump is such that the flowrate at the required discharge pressure is greater than the desired flowrate?
                          I assume the OPV is used to control the discharge pressure, so it may be possible to adjust the OPV to a higher pressure (thus reducing the flowrate) and compensating for this via the addition or a pressure reducing valve downstream of the OPV (providing sufficient pressure drop to give 9 barg at the puck).

                          My pump design is a bit rusty, but I think that is how fixed speed pumps are controlled?

                          Edit: I just read through the rest of this thread. If your aim is pressure profiling, cant you just add a valve upstream of the boiler?

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                          • #14
                            Originally posted by MrJack View Post
                            Could the OPV be discharging because the pump is oversized? That is to say, the design of the pump is such that the flowrate at the required discharge pressure is greater than the desired flowrate?
                            I assume the OPV is used to control the discharge pressure, so it may be possible to adjust the OPV to a higher pressure (thus reducing the flowrate) and compensating for this via the addition or a pressure reducing valve downstream of the OPV (providing sufficient pressure drop to give 9 barg at the puck).

                            My pump design is a bit rusty, but I think that is how fixed speed pumps are controlled.?
                            Eh? What's the point of adjusting the OPV to a higher pressure and putting another downstream? The point of the OPV is to do exactly what you described (provide ). xbar at the puck. It's supposed to be constantly discharging. Pump provides 14-15bar pressure and the OPV discharges anything over 9bar (or whatever) to provide constant, consistent static pressure at the puck.

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                            • #15
                              Re: ulka pump power reduction

                              Ive just realised these are a PD vibe pump - throttling the discharge wont change the flowrate on these it seems, which is probably why they use bypass control valves (OPVs).

                              Still suggests the pump is oversized for the application.
                              Last edited by MrJack; 9 April 2013, 10:29 AM.

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