Pump cavitation help.
  • C_BC_B
    Posts: 89,069
    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?
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  • jeepinjeepinjeepinjeepin
    Posts: 18,099
    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: 18,099
    A ball valve to throttle the discharge will help.
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  • C_BC_B
    Posts: 89,069
    jeepinjeepin said:

    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
  • JayrizzleJayrizzle
    Posts: 90,691
    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.
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  • 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: 122,708
    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: 18,099
    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: 89,069
    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
  • JayrizzleJayrizzle
    Posts: 90,691
    get a spray bottle and mist that copper bit with cool water and your problem will go away.
    image
  • JayrizzleJayrizzle
    Posts: 90,691
    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.
    image
  • JayrizzleJayrizzle
    Posts: 90,691
    Also try a gate valve after the pump. Greater outflow pressure means greater (lower vacuum) inflow pressure.
    image
  • ThymThym
    Posts: 122,708
    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: 89,069
    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
  • JayrizzleJayrizzle
    Posts: 90,691
    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.
    image
  • JayrizzleJayrizzle
    Posts: 90,691
    regardless of the pressure, the pump will add some heat so you'll have to be somewhat below boiling to use the pump.
    image
  • ThymThym
    Posts: 122,708
    Dr_Jerryrigger said:

    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: 89,069
    So the pump is no bueno for the boil. I don't fully believe that.
    "On it. I hate software." ~Cpt Snarklepants
  • ThymThym
    Posts: 122,708
    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: 122,708
    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: 89,069
    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: 122,708
    image
    The only thing between me and a train wreck is blind luck..... - Kenny
  • ThymThym
    Posts: 122,708
    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
  • JayrizzleJayrizzle
    Posts: 90,691
    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).
    image
  • JayrizzleJayrizzle
    Posts: 90,691
    and why are you doing this?
    image
  • ThymThym
    Posts: 122,708
    Dr_Jerryrigger said:

    and why are you doing this?


    to mess with you
    The only thing between me and a train wreck is blind luck..... - Kenny
  • ThymThym
    Posts: 122,708
    Dr_Jerryrigger said:

    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).



    interestingly, with this type of dynamic pump, even shutting the outlet flow off completely wont result in a 0 psi drop. it's still spinning the fluid around really frikin fast and that results in a static pressure difference that will induce flow within the pump head and result in a slight negative pressure at the center-most point of the rotating machinery.
    The only thing between me and a train wreck is blind luck..... - Kenny
  • C_BC_B
    Posts: 89,069
    Lakewood said:

    Dr_Jerryrigger said:

    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).



    interestingly, with this type of dynamic pump, even shutting the outlet flow off completely wont result in a 0 psi drop. it's still spinning the fluid around really frikin fast and that results in a static pressure difference that will induce flow within the pump head and result in a slight negative pressure at the center-most point of the rotating machinery.

    Thus resulting in the cavitation regardless how far closed the valve is.
    "On it. I hate software." ~Cpt Snarklepants
  • C_BC_B
    Posts: 89,069
    Dr_Jerryrigger said:

    and why are you doing this?


    To clean and sanitize the lines and pump head. That I've already cleaned.
    "On it. I hate software." ~Cpt Snarklepants
  • ThymThym
    Posts: 122,708
    C_B said:

    Lakewood said:

    Dr_Jerryrigger said:

    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).



    interestingly, with this type of dynamic pump, even shutting the outlet flow off completely wont result in a 0 psi drop. it's still spinning the fluid around really frikin fast and that results in a static pressure difference that will induce flow within the pump head and result in a slight negative pressure at the center-most point of the rotating machinery.

    Thus resulting in the cavitation regardless how far closed the valve is.


    if its really 212 deg F at the pump, yes. but it's unlikey that you will have 0 heat loss, so it's kinda sorta possible to run it slow enough to not cavitate at boiling...
    The only thing between me and a train wreck is blind luck..... - Kenny
  • jeepinjeepinjeepinjeepin
    Posts: 18,099
    In conclusion, either let it come off boil before pumping or run a large copper drain from near the bottom of the kettle straight down to the pump 2' below.
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  • JayrizzleJayrizzle
    Posts: 90,691
    Lakewood said:

    Dr_Jerryrigger said:

    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).



    interestingly, with this type of dynamic pump, even shutting the outlet flow off completely wont result in a 0 psi drop. it's still spinning the fluid around really frikin fast and that results in a static pressure difference that will induce flow within the pump head and result in a slight negative pressure at the center-most point of the rotating machinery.


    Regardless of pressure drop, a spinning thing will add heat. At my place of work we make one product that uses 25kg of butter, if not heated enough; we soften it by mixing it for a long time in a massive blender. It's a crappy way of heating things if you're trying to heat, but it has an effect that shouldn't be ignored. If just the pressure drop was to blame a closed valve would cause bubbles that quickly condensed.

    And with out movement any where is that 1/6th hp(give or take a lot) going? Really a variable speed thing would be best.


    Yeah like i said a wile back, to sanitize, just let it run into a bucket with out the pump running. To pump it somewhere; let it cool down a little.
    image
  • ceanntceannt
    Posts: 53,828
    This thread reminds me why I like gravity ..... you guys are making my head hurt ....
    Never attribute to malice, that which can adequately be explained by stupidity.
  • ceanntceannt
    Posts: 53,828
    I have ran a lot of calcs for pumps ... but never at boiling .... sanitary force mains rarely get that hot .... unless scoob is involved
    Never attribute to malice, that which can adequately be explained by stupidity.
  • ThymThym
    Posts: 122,708
    ceannt said:

    I have ran a lot of calcs for pumps ... but never at boiling .... sanitary force mains rarely get that hot .... unless scoob is involved


    Ha
    The only thing between me and a train wreck is blind luck..... - Kenny
  • morsmors
    Posts: 231
    I run my march pump at boiling temps all the time. (Not accounting for temp loss in the hose to the pump). Just make sure the out valve is facing straight up (I find even a slight tilt will have a large impact on cavitation). I run wort through my pump and plate chiller for the last 15-20 mins of my boil.
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  • ThymThym
    Posts: 122,708
    mors said:

    I run my march pump at boiling temps all the time. (Not accounting for temp loss in the hose to the pump). Just make sure the out valve is facing straight up (I find even a slight tilt will have a large impact on cavitation). I run wort through my pump and plate chiller for the last 15-20 mins of my boil.



    Interesting. I suppose having the outlet stright up would help remove the vapor quickly. I might have to try experimenting.
    The only thing between me and a train wreck is blind luck..... - Kenny
  • C_BC_B
    Posts: 89,069
    Outlet straight up.
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  • C_BC_B
    Posts: 89,069
    Mors, what configuration do you have in the kettle? False bottom? Dip tube? Straight inlet? 1/2" ball valve?
    "On it. I hate software." ~Cpt Snarklepants
  • morsmors
    Posts: 231
    It's a 1/2" ball valve with 1/2 silicone tubing. I have a 1/2" coupler on the inside of the kettle but nothing screwed into it so no dip tube atm (I just tilt it when it gets lower).
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  • morsmors
    Posts: 231
    I should note I do have some restriction due to the shitty QD I use. I have these atm...
    http://morebeer.com/products/kent-male-qd-12-mpt.html

    But if anything they should make it more likely to cavitate...
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  • C_BC_B
    Posts: 89,069
    mors said:

    I should note I do have some restriction due to the shitty QD I use. I have these atm...
    http://morebeer.com/products/kent-male-qd-12-mpt.html

    But if anything they should make it more likely to cavitate...



    Ha! Those are the cheapos I have to install. I think the problem with mine is the diptube. I think I'll install a couple recirc ports and plan on drawing off the topish and returning at the bottomish.
    "On it. I hate software." ~Cpt Snarklepants
  • C_BC_B
    Posts: 89,069
    Then pulling off the bottom to run to the fermentor.
    "On it. I hate software." ~Cpt Snarklepants
  • morsmors
    Posts: 231
    yeah the Kent disconnects 'work' but they do restrict flow alot... Need to drop a good $200 and get some stainless and end my suffering though.
    BJCP A0936 National Beer Judge and Mead Judge
    Cicerone Certified Beer Server
    AHA Member
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    HBT "mors"
  • C_BC_B
    Posts: 89,069
    mors said:

    yeah the Kent disconnects 'work' but they do restrict flow alot... Need to drop a good $200 and get some stainless and end my suffering though.


    I would like full bore cam locks, but I'm not dropping that kind of cheddar on a hobby.
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  • morsmors
    Posts: 231
    I'm a gadget whore. What's the point of a hobby if you can't immerse yourself fully in it lol ;-)
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  • ThymThym
    Posts: 122,708
    mors said:

    I'm a gadget whore. What's the point of a hobby if you can't immerse yourself fully in it lol ;-)



    Yay, toys!
    The only thing between me and a train wreck is blind luck..... - Kenny
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