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Whirlpooling: Pump Curves Make My Head Hurt

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  • Whirlpooling: Pump Curves Make My Head Hurt

    So we've been talking about applying some actual science to our whirlpool speed, rather than "eh, looks about right." Considering our current practice is 1) get it spinning with the steel paddle, 2) turn on the VFD until the pump's just starting to make annoying noise, then 3) throttle the whirlpool valve until it stops making annoying noise...yeah it's probably time to take a closer look. Thus I've spent the morning trying to figure out from the pump curve on our Ampco AC+ 1 horse 1.5" pump what the flow rate is. And now it's two hours later and my head hurts.

    The MBAA Practical Handbook #1 (totally pick these up BTW!) says whirlpool transfers should go in about 7-8 feet per second flow velocity. It gives the formula:

    V = (0.408 x GPM)/D2

    Where V is wort velocity, GPM is gallons per minute and D is inner pipe diameter.

    This is for transfer to a separate whirlpool, and ours is combined, but I imagine the idea is to spin the kettle about as long as you would take to transfer to a separate whirlpool, 10-15 minutes. So:

    If we want to transfer (i.e. spin) 11bbls in 10 minutes we need to go at:

    GPM = (11bbl x 31gal/bbl)/10 min = 34.1

    Our pipe diameter is 1.5" so D squared is 2.25

    So V = (0.408 x 34.1 gpm)/2.25 or 6.18 ft/sec. So a bit slow actually. But it's 7.25 ft/sec at 40 gal/min. So let's set that as the target flow rate. Which makes sense. A little over a barrel a minute to transfer 11bbls in about 10 minutes.

    Now to the pump curve. Ugh. So here's the curve for my pump. It's got a 1 horse powering it. Of course, I have no idea without unshipping it what the impeller diameter is, but I'm going to guess probably 3.5" since it's got a one horse on it.

    Looking at the curve, if I want 40 gpm it should be somewhere between 3/4 and 1 horse. Which would be like 85% on the VFD, which is WAY faster than we've been running it. Is this right? How much should we throttle down the pump with the VFD? Or am I obviously not a fluid process engineer and reading the chart wrong?
    Russell Everett
    Co-Founder / Head Brewer
    Bainbridge Island Brewing
    Bainbridge Island, WA

  • #2
    Russ, I think the Kunze/Denk came up with 3.5 cubic meters/second is optimum. I think the often overlooked problem is the shear forces in a smaller pump head that can break up all that good floc. I've found that I only need to get the whirlpool moving to get a good pile. My whirlpool time is under 3 min with 3 speeds on my vfd. I only really crank it for 30 seconds. While I was working at a large craft I did some experiments on different speeds and found them to be inconclusive. Just a little movement will result in a good pile, as long as your vessel is shaped correctly

    Comment


    • #3
      Hey Russell, I don't think you can interpolate VFD settings from these curves because they're all for a pump operating at 3500 rpm. Even if that wasn't the case, I don't think setting a VFD to 85% necessarily results in a pump operating at 85% of its horsepower. If you can find a way to ballpark the rpm of your whirlpool near the side of the tank (although not necessarily right at the edge because the wall will slow down the wort), you can use the circumference of your tank to estimate the wort's velocity. It may be as simple as watching hop particles swirl around. Otherwise, you could add something inert that barely floats and take it out before knockout.

      You may not need to stir the wort with a paddle either. As far as I'm aware, "time at speed" doesn't mean much. What's important is achieving sufficient rotational velocity by the time the rest starts, which a pump should be able to accomplish over the course of 10-15 minutes. The slowdown during the rest is what actually forces particles to the bottom center of the tank.

      It's not very science-y, but I hope it helps!

      Joe

      Comment


      • #4
        Yeah that's part of the problem. The VFD at 50% doesn't mean the horsepower is 50%, it means the amperage and presumably thus the RPMs are 50%. So that'd be the 1750 RPM curve http://www.ampcopumps.com/media/1903...15x15_1750.pdf one would think. But my head still hurts.

        @LongLiveLagers - Just tryin to get sciency all up in this biatch! We've tried a variety of different speeds, times, rests, stirring/not stirring, pumping/not-pumping and we've got a regimen that works pretty well most of the time now. But just because 'that's how we've been doing it' doesn't mean it's the best way to do it. And if I could get a tighter cone on our IIPA I could jam a few more pounds of whirlpool hops in there...
        Russell Everett
        Co-Founder / Head Brewer
        Bainbridge Island Brewing
        Bainbridge Island, WA

        Comment


        • #5
          Ah so that's why...

          Comment


          • #6
            Haha yeah. That's why the current protocol is 'turn it up until it starts making awful noises and vibrations'.
            Russell Everett
            Co-Founder / Head Brewer
            Bainbridge Island Brewing
            Bainbridge Island, WA

            Comment


            • #7
              I know this pain all too well myself. However the knowledge that I gained today about these pump curves will be useful to have in the future.
              Justin Crawford
              Head Brewer
              Valholl Brewing Co. LLC
              Poulsbo, Washington

              Comment


              • #8
                The Kunze say clearly

                Originally posted by LongLiveLagers View Post
                Russ, I think the Kunze/Denk came up with 3.5 cubic meters/second is optimum. I think the often overlooked problem is the shear forces in a smaller pump head that can break up all that good floc. I've found that I only need to get the whirlpool moving to get a good pile. My whirlpool time is under 3 min with 3 speeds on my vfd. I only really crank it for 30 seconds. While I was working at a large craft I did some experiments on different speeds and found them to be inconclusive. Just a little movement will result in a good pile, as long as your vessel is shaped correctly
                Not over 3.5 mtr/sec flow rate. Optimal is 2.8 to 3.3. rest not over 15 min as you increase your TBI.

                Comment


                • #9
                  It sounds to me like you have more problems than just pump speed. Those "awful noises and vibration" are caused by cavitation and are eroding your impeller and possibly backplate. You may get to measure the diameter of what's left of your impeller soon. Cavitation isn't doing your wort any good, either.

                  Cavitation is caused by low pressure at the impeller--the water instantly vaporizes into tiny bubbles which then instantly collapse with implosion pressures difficult to imagine--some comparisons have been made to the pressures of an atomic explosion. Tiny pits begin to form in the impeller, which then become nucleation points for further cavitation, leading to an increasingly rapid erosion of the impeller.

                  Check that the lines--pipes or hoses--to the inlet of the pump are large enough (at least as big as the pump inlet), short as possible, and with little or no restriction (a 90 L is equivalent to about 3' of straight pipe; pulling off the boss of a T is much worse). A 1hp pump isn't very big, and should be able to run full speed without cavitating.
                  Timm Turrentine

                  Brewerywright,
                  Terminal Gravity Brewing,
                  Enterprise. Oregon.

                  Comment


                  • #10
                    Kunze

                    @Gatamo, interesting comment about TBI. I was wondering, do you pre-chill casting wort from the kettle before whirlpooling, ie from 100C to 85C? I haven't seen anybody in north america following this procedure.


                    Originally posted by WaterEng
                    Careful Timm, the hydraulics of the piping and system on the inlet side of the pump can easily create problems for even a small pump. Cavitation is possible for any pump depending on its installation and use.

                    Comment


                    • #11
                      Originally posted by WaterEng
                      Careful Timm, the hydraulics of the piping and system on the inlet side of the pump can easily create problems for even a small pump. Cavitation is possible for any pump depending on its installation and use.
                      That being exactly my point. If inlet-side plumbing is correctly set up, the pump should be able to run full-speed without cavitation.
                      Timm Turrentine

                      Brewerywright,
                      Terminal Gravity Brewing,
                      Enterprise. Oregon.

                      Comment


                      • #12
                        Part of the noise was that the friction disc on the pump head was heating up, making a lovely high pitched squeal when you ran hot things through it at high speed. I added a small line off our deck hose that drips water on the drive shaft and now we can run cast out and whirlpool about 5 hz faster without earsplitting noise. Still get some vibration at very high speed, but that pump is clamped straight onto the steel brewdeck.
                        Russell Everett
                        Co-Founder / Head Brewer
                        Bainbridge Island Brewing
                        Bainbridge Island, WA

                        Comment


                        • #13
                          Originally posted by Bainbridge View Post
                          Part of the noise was that the friction disc on the pump head was heating up, making a lovely high pitched squeal when you ran hot things through it at high speed. I added a small line off our deck hose that drips water on the drive shaft and now we can run cast out and whirlpool about 5 hz faster without earsplitting noise. Still get some vibration at very high speed, but that pump is clamped straight onto the steel brewdeck.

                          Good, then, not cavitation.

                          Sounds like you should have a new seal for that pump on hand, 'though.
                          Timm Turrentine

                          Brewerywright,
                          Terminal Gravity Brewing,
                          Enterprise. Oregon.

                          Comment


                          • #14
                            Originally posted by TGTimm View Post
                            Sounds like you should have a new seal for that pump on hand, 'though.
                            Always keep at least one pump seal kit around!
                            Russell Everett
                            Co-Founder / Head Brewer
                            Bainbridge Island Brewing
                            Bainbridge Island, WA

                            Comment


                            • #15
                              So the science part makes my head hurt too...

                              The way I am reading it you have a paddle in your vessel. That will screw with your cone formation completely. I spent a little time on a small system with a mash kettle and found that I got the best cone I could get by spinning it with the mixer and using the ramp function on the VFD to have it slow down slowly over whatever the max time allowed was. If I spun it with the pump and left the mixer stationary it disturbed the whirlpool too much.

                              I am back on the DME system I came from now and have applied the same thing here. No paddle so I run the pump up to where the pump just starts to cavitate and back it off. That is 45/60 on my system. I spin it for 15 minutes and then set the ramp to slow the pump down over 999 seconds (max allowed). I get really tight cones as long as it is a full batch. Half batches dont react as well.
                              Mike Pensinger
                              General Manager/Brewmaster
                              Parkway Brewing Company
                              Salem, VA

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