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Pump cavitation help.
  • C_BC_B
    Posts: 77,626
    So here's a pic of my pump configuration right at the moment. I have QDs to hook up and get rid of that long copper pipe, I just haven't done it. The problem is the pump cavitates (right term?) while the kettle is boiling. I'd like to recirc the wort for the last couple minutes of the boil to sterilize the pump head and lines if possible. I assume this is due to the pressure drop at the pump head causing the wort to boil in the pump head thus not allowing it to pump. Moving forward when I get around to building a rig of some type I'd like to design this issue out if possible.
    How much lower will I have to mount the pump to overcome that pressure drop? If I add a pickup point for the recirc at around the 5-7 gallon level will that help?
    IMAG0944.jpg
    2560 x 1440 - 575K
    "On it. I hate software." ~Cpt Snarklepants
  • jeepinjeepinjeepinjeepin
    Posts: 17,331
    There is a mathematic formula to solve this problem. I think you gain 0.46 psi for every 10' of head.
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  • jeepinjeepinjeepinjeepin
    Posts: 17,331
    A ball valve to throttle the discharge will help.
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  • C_BC_B
    Posts: 77,626

    A ball valve to throttle the discharge will help.



    Yeah... I've tried nearly every option here. Cutting it back to 10% still does nothing.
    "On it. I hate software." ~Cpt Snarklepants
  • JerryJerry
    Posts: 75,485
    So you're having problems with heat and pressure. Chang one of those. Let it pour into a bucket to sanitize. Then let it cool down for a few min.
    "Again?"
    CurlyFat's 60,000th post
  • scoobscoob
    Posts: 16,617
    My pump was doing the same thing, I was drawing into the pump via my lower port which also has a dip tube pointing down attached, during a full boil the bubbles coming off the bottom were simply being drawn into the pump causing cavitation at best, completely stopping pump flow at its worst. I tried it with water to confirm, nixed the downturn on my pickup and it solved my problem.
    Jesus didn't wear pants
  • ThymThym
    Posts: 103,739
    Where the outlet is located on the tun will not effect the head pressure.

    Only the height of the top surface of the liquid above the pump will matter.

    What pump are you running?
    The only thing between me and a train wreck is blind luck..... - Kenny
  • jeepinjeepinjeepinjeepin
    Posts: 17,331
    Lakewood said:

    Where the outlet is located on the tun will not effect the head pressure.

    Only the height of the top surface of the liquid above the pump will matter.

    What pump are you running?



    It should by a foot or so, wouldn't it?
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  • C_BC_B
    Posts: 77,626
    Scoob, so using a port located at the 5 gallonish level that is turned horizontal should work?

    Lake, March 80whatevereveryoneelseuses. Also, I thought as much about head pressure being relative to the top surface of the liquid.

    The diptube may be the cause?
    "On it. I hate software." ~Cpt Snarklepants
  • JerryJerry
    Posts: 75,485
    get a spray bottle and mist that copper bit with cool water and your problem will go away.
    "Again?"
    CurlyFat's 60,000th post
  • JerryJerry
    Posts: 75,485
    You just need to be a few degrees below where you are, or reduce vacuum by getting a smaller pump. Upping your pipe size might help (might). Using more copper pipe so things cool more before the pump might help.
    "Again?"
    CurlyFat's 60,000th post
  • JerryJerry
    Posts: 75,485
    Also try a gate valve after the pump. Greater outflow pressure means greater (lower vacuum) inflow pressure.
    "Again?"
    CurlyFat's 60,000th post
  • ThymThym
    Posts: 103,739
    C_B said:

    Scoob, so using a port located at the 5 gallonish level that is turned horizontal should work?

    Lake, March 80whatevereveryoneelseuses. Also, I thought as much about head pressure being relative to the top surface of the liquid.

    The diptube may be the cause?



    dip tube can help if its actually picking up vapor. really depends on the temp going in to the pump. they will cavitate if the temp is near boiling.
    The only thing between me and a train wreck is blind luck..... - Kenny
  • C_BC_B
    Posts: 77,626
    Lakewood said:

    C_B said:

    Scoob, so using a port located at the 5 gallonish level that is turned horizontal should work?

    Lake, March 80whatevereveryoneelseuses. Also, I thought as much about head pressure being relative to the top surface of the liquid.

    The diptube may be the cause?



    dip tube can help if its actually picking up vapor. really depends on the temp going in to the pump. they will cavitate if the temp is near boiling.

    So if its near boiling it will cavitate period? Regardless?
    "On it. I hate software." ~Cpt Snarklepants
  • JerryJerry
    Posts: 75,485
    C_B said:

    Lakewood said:

    C_B said:

    Scoob, so using a port located at the 5 gallonish level that is turned horizontal should work?

    Lake, March 80whatevereveryoneelseuses. Also, I thought as much about head pressure being relative to the top surface of the liquid.

    The diptube may be the cause?



    dip tube can help if its actually picking up vapor. really depends on the temp going in to the pump. they will cavitate if the temp is near boiling.

    So if its near boiling it will cavitate period? Regardless?


    Unless it's not pulling that hard.
    "Again?"
    CurlyFat's 60,000th post
  • JerryJerry
    Posts: 75,485
    regardless of the pressure, the pump will add some heat so you'll have to be somewhat below boiling to use the pump.
    "Again?"
    CurlyFat's 60,000th post
  • ThymThym
    Posts: 103,739

    regardless of the pressure, the pump will add some heat so you'll have to be somewhat below boiling to use the pump.



    that's not really the thermodynamic principal at work here, but the resulting advice is still the same, so yeah, close enough.
    The only thing between me and a train wreck is blind luck..... - Kenny
  • C_BC_B
    Posts: 77,626
    So the pump is no bueno for the boil. I don't fully believe that.
    "On it. I hate software." ~Cpt Snarklepants
  • ThymThym
    Posts: 103,739
    C_B said:

    Lakewood said:

    C_B said:

    Scoob, so using a port located at the 5 gallonish level that is turned horizontal should work?

    Lake, March 80whatevereveryoneelseuses. Also, I thought as much about head pressure being relative to the top surface of the liquid.

    The diptube may be the cause?



    dip tube can help if its actually picking up vapor. really depends on the temp going in to the pump. they will cavitate if the temp is near boiling.

    So if its near boiling it will cavitate period? Regardless?


    if its a couple degrees below boiling you should be fine. if it's actually boiling in the kettle it's gonna cavitate in the pump.
    The only thing between me and a train wreck is blind luck..... - Kenny
  • ThymThym
    Posts: 103,739
    C_B said:

    So the pump is no bueno for the boil. I don't fully believe that.



    you don't usually pump wort while it's at a rolling boil...
    The only thing between me and a train wreck is blind luck..... - Kenny
  • C_BC_B
    Posts: 77,626
    Lakewood said:

    C_B said:

    So the pump is no bueno for the boil. I don't fully believe that.



    you don't usually pump wort while it's at a rolling boil...


    I suppose that's a fair point.
    "On it. I hate software." ~Cpt Snarklepants
  • ThymThym
    Posts: 103,739
    image
    The only thing between me and a train wreck is blind luck..... - Kenny
  • ThymThym
    Posts: 103,739
    you can gueestimate your gauge pressure at the impeller to be somewhere in the neighborhood of -2 to -5psi depending on flow rate, of course if you have a very large static head from mounting the pump a few feet below the fluid level, you could conceivably offset that by a couple psi.
    The only thing between me and a train wreck is blind luck..... - Kenny
  • JerryJerry
    Posts: 75,485
    So like I've been saying, reduce the vacuum and or reduce the temp at the pump. You have a ball valve just after the pump. Turn that nearly off so that only a little trickle gets by. Add a longer hose before the pump, or find some way of cooling it a little (like a bucket of cool water).
    "Again?"
    CurlyFat's 60,000th post
  • JerryJerry
    Posts: 75,485
    and why are you doing this?
    "Again?"
    CurlyFat's 60,000th post
  • ThymThym
    Posts: 103,739

    and why are you doing this?


    to mess with you
    The only thing between me and a train wreck is blind luck..... - Kenny