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Thread: ulka pump power reduction

  1. #1
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    ulka pump power reduction

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    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?

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    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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    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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    Senior Member Dragunov21's Avatar
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    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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    what direction is upstream?

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

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    Quote 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.

    Quote 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.

    Quote 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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    Senior Member Dragunov21's Avatar
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    Quote 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 96C 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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    Not a Shoe Jimmytheboot's Avatar
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    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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    Senior Member Dragunov21's Avatar
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    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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    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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    Senior Member Dragunov21's Avatar
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    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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    Senior Member deegee's Avatar
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    Quote 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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    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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    Senior Member Dragunov21's Avatar
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    Quote 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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    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; 9th April 2013 at 10:29 AM.

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    Senior Member Dragunov21's Avatar
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    How so? I'd suggest it's oversized to provide a consistent 9bar after the OPV at a range of flow-rates?

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    Re: ulka pump power reduction

    Espresso machines need to operate at a range of flowrates? Or are you saying it is used for a range of espresso equipment with different flowrate capacity requirements?

    Its oversized for the application (I guess you could say its not optimised). Going from information in this thread it is designed to operate at 155% of the required pressure, at a flowrate 3-4 times the required rate.

    Its not a criticism, just a statement.

    Interestingly, looking at the pump curve for the ulka E5, it will produce 60mL/min at ~13.5 barg (~250mL @ 9barg). Still not sure if this can be acheived by the method I described earlier, but should be easy enough to test.

  18. #18
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    I mean that an ideal single shot will flow at a lower rate than will a double as will a double compared to a triple, so you need some a pump that can cope with the maximum flowrate that might be required.

    I'm also don't know what the output of a vib-pump is like, but if it fluctuates cyclically you'd size it such that the minimum pressure during operation did not drop below the OPV's set pressure (ie to get 9bar, you'd need something that doesn't drop below 9bar rather than something that peaks at or operates at an average of 9bar). Happy to be told that's not the case though.

    Another consideration is that these machines are also designed for use with pods, which require higher pressures (11-12bar IIRC), so they're not as oversized as you might imagine.

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    Re: ulka pump power reduction

    Im not sure the requirement to do doubles and triples accounts for the flowrate capacity being so high.

    I think its more likely its a result of using bypass pressure control (requiring a waste stream flowrate proportional to the difference in pressure drop between the two flow paths), and a generic pump design.

    In terms of the pressure fluctuations, you could be right - no idea how they behave.

    Regardless, the OP was looking for a way to alter the puck pressure. It would be interesting to determine if adjusting the OPV affects the pump flowrate. If so, it suggests a manual valve (perhaps actually upstream of the OPV) may acheive this aim.

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    Not a Shoe Jimmytheboot's Avatar
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    Quote Originally Posted by MrJack View Post
    Regardless, the OP was looking for a way to alter the puck pressure. It would be interesting to determine if adjusting the OPV affects the pump flowrate. If so, it suggests a manual valve (perhaps actually upstream of the OPV) may acheive this aim.
    C-man did this and made a thread about it

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    Senior Member Dragunov21's Avatar
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    Quote Originally Posted by MrJack View Post
    Im not sure the requirement to do doubles and triples accounts for the flowrate capacity being so high.

    I think its more likely its a result of using bypass pressure control (requiring a waste stream flowrate proportional to the difference in pressure drop between the two flow paths), and a generic pump design.

    In terms of the pressure fluctuations, you could be right - no idea how they behave.

    Regardless, the OP was looking for a way to alter the puck pressure. It would be interesting to determine if adjusting the OPV affects the pump flowrate. If so, it suggests a manual valve (perhaps actually upstream of the OPV) may acheive this aim.
    Well no (doubles/triples), but it's a factor. I suspect part of it is simply that it was the closest/cheapest above-spec part available. The pumps aren't specifically manufactured for the machines, as you've said.

    Adjusting the OPV wouldn't affect the flowrate through the pump appreciably, I believe, as any excess is discharged freely. I'm not too au-fait on pumps though.

    As for using a valve upstream, I don't understand why you'd bother when you have a perfectly good steam-valve that will do the same job. You also have to consider that restricting the flow upstream of the OPV's discharge line might damage the pump. I don't know whether or not restricting it to less than its rated flow would damage it, but I'd be making sure first.

  22. #22
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    Did someone say Frankensilvia?

    I had too much time on my hands and too many spare Silvia boilers last week. I made a second steam boiler that occupies half the water reservoir area. It has an autofill controller, PID on brew boiler and a pre-heating loop in the steam boiler. Brew boiler gauge feeds directly from the shower screen. I messed around with the idea of variable pump pressure but settled on an 0.6mm restrictor jet at the solenoid, this slows down the delivery rate for a reasonable pre-infusion. Would be nice to wind down the pressure during the shot though, might try some tests with the pump hooked up to a variac.
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    Re: ulka pump power reduction

    Oh, nice! :thumbup:

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    I'd like to see what the variac does; as I said, I don't know if you need VFVV or just VV

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    Quote Originally Posted by coffee_machinist View Post
    Did someone say Frankensilvia?

    I had too much time on my hands and too many spare Silvia boilers last week. I made a second steam boiler that occupies half the water reservoir area. It has an autofill controller, PID on brew boiler and a pre-heating loop in the steam boiler. Brew boiler gauge feeds directly from the shower screen. I messed around with the idea of variable pump pressure but settled on an 0.6mm restrictor jet at the solenoid, this slows down the delivery rate for a reasonable pre-infusion. Would be nice to wind down the pressure during the shot though, might try some tests with the pump hooked up to a variac.
    I have seen this in the metal and to say it's freakish (in an amazeballs way) is an understatement. HX fed Silvia brew boiler and 2 x Silvia boilers for steam. You then hook the whole shebang up to a PID and Minore control board and solve the plumbing and thermodynamics. PID, steam and brew pressure gauges all in the front panel as well.

    If there is anything like this anywhere else in the world, I am yet to see it.

    This is just another example of Rick's incredible talent.

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    hx fed brew boiler sounds perfect for both temperature stability and having a minimal amount of water sitting deoxygenating.



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