Ask The Brewmasters

Back to discussions
Expand all | Collapse all

Hot liquor pump pressure loss

  • 1.  Hot liquor pump pressure loss

    Posted 12-09-2022 16:57

    All,

    I have a pump problem (shocking) that I have been dealing with/living with for several months now, and I'm hoping to find a remedy for it after trying everything to eliminate this ghost in the machine. My hot liquor pump consistently loses pressure during sparging/knockout loop sterilization, when water temperature has increased and hot liquor volume has decreased. The pump behaves fine during vessel rinsing and mash in, but once I've increased the temp of the hot liquor for sparging (170) it gradually loses pressure until the flow out of the sparge is barely a trickle. Looking at the pump curve, like most pumps there is a loss of pressure with increased temperature, but this is an incredibly drastic condition. After I've completed wort knockout, and the water volume in the hot liquor tank has increased, full pressure resumes during final vessel rinsing. The water temp has decreased at this point and usually lands around 160. 

    I've replaced the seal kit on the pump, tightened and reseated every connection to and from the pump to eliminate any air being pulled in, removed the check valve (piping into brewhouse passes through two) on the brewhouse side, and installed a vortex breaker on the drain of the HLT to help eliminate any vortexes being pulled into the pump. I've talked to the brewhouse manufacturer (BrauKon), pump manufacturer (Grundfos), local service provider for the pump, and about every brewer in town about this issue, and nothing we have tried has solved this problem.

    Any ideas would be greatly appreciated, thanks for any help! 



    ------------------------------
    Aaron Dahl
    Head Brewer
    Golden Age Beer
    Homestead, PA
    ------------------------------


  • 2.  RE: Hot liquor pump pressure loss

    Posted 12-09-2022 21:41
    Hey Aaron,

    Whats your water mineral content like? I'm assuming that you HX is included in your KO sterlization loop, and also assuming your pump has successfully performed these operations before. Is it possible there is some mineral scale inside the HX? That added resistance could be increasing your pressure drop, and combined with the decreasing water level in the HLT as you sparge....Just trying to think outside the box.

    ------------------------------
    Weston Barkley
    Head Brewer
    Great Notion Brewing
    Portland OR
    ------------------------------



  • 3.  RE: Hot liquor pump pressure loss

    Posted 12-12-2022 12:40

    Sounds to me like you may be starving the pump. There may be an obstruction in the line between the tank and the pump (gasket, mineral buildup). With a full tank the head pressure may be helping to overcome the restriction. On the other hand, higher temperature could exacerbate the problem as vapor pressure decreases and the system becomes more susceptible to cavitation.



    ------------------------------
    Santiago Gomez
    Director of Technology
    Apotek Solutions LLC
    Beverly Hills MI
    (734) 455-7770
    ------------------------------



  • 4.  RE: Hot liquor pump pressure loss

    Posted 12-12-2022 12:41
    Hi,

    What size is your system? What kind of flow rate are you trying to achieve? How much hydrostatic pressure do you have feeding the inlet of the pump toward the end of your sparge? How much head pressure are you trying to achieve? Sounds like your pump is starving for inlet flow as the temp increase and you lose hydrostatic pressure on the inlet.

    Cheers
    Joe

    ------------------------------
    Joe Williams
    UC Davis
    Davis CA
    (530) 754-5766
    ------------------------------



  • 5.  RE: Hot liquor pump pressure loss

    Posted 12-12-2022 12:42
    Hello Aaron,

    This sounds like a Net Positive Suction Head (NPSH) issue, particularly since it relates to both a temperature increase and a level drop in the HLT.  From your description, I assume the problem developed over time.  I'm not sure how far your basic troubleshooting went, but here are my suggestions for getting to the root cause.
    1. Run the pump and listen for the telltale sign of cavitation in the pump when the condition occurs.  If present, insufficient NPSH at the eye of the impeller is likely the problem.
    2. Disassemble the pump and thoroughly inspect the inlet path and impeller for wear or clogging/foreign matter in the inlet eye and vanes.
    3. Install a pressure gauge on the pump inlet if possible and compare that pressure to the NPSH required by the pump at the required flow rate. Use the pump curve from Grundfos for your specific pump and impeller combination.
    4. Check if the piping has a rise, loop, long leg, or restriction that could cause the water pressure to be pulled down below the flash point (boiling point) at 170 degrees. It doesn't take much vacuum (8-10 PSIA, 14.7 PSIA is approximately sea level) to cause water vapor to form in the pipe or pump suction.  It is surprising how little a change in suction conditions with hot liquids can cause NPSH problems, particularly as flow increases. 

    I hope this adds to the process and helps you find the root cause of the problem.

    Harlan Coomes
    Dipl.Brew





  • 6.  RE: Hot liquor pump pressure loss

    Posted 12-12-2022 15:30
    Hi Aaron,
    Is this loss of flow coupled with a change in the sound coming from the pump? Maybe a low rattling noice? If so, that's cavitation. It's possible you have dropped below the Net Positive Suction Pressure Required (NPSP-R)? If you've spoken to the pump manufacturer, I'm guessing you already investigated this. But, if low NPSP is the cause, there are a few options. 
    1) Increase the volume (height) of liquid in the tank
    2) Decrease the distance from Tank Outlet to Pump Suction
    3) Remove restrictions like Tees, Ells, Valves etc on Suction Side so that there is less restriction feeding the pump
    4) Increase diameter of Suction Side pipe
    The NPSP-R can be found on your Pump Curve (corrected for Water Vapor Pressure/Temp). Then the Pump Manufacturer should help you determine your System NPSP. That must be greater than your NPSP-R for the pump to operate at a given flow rate/pressure. Sounds complicated but it's not for a willing Pump Engineer.
    Good Luck,
    Dan Carey
    New Glarus Brewing Company

    ------------------------------
    Daniel Carey
    Brewmaster
    New Glarus Brewing Company
    New Glarus WI
    (608) 527-5850
    ------------------------------



  • 7.  RE: Hot liquor pump pressure loss

    Posted 12-12-2022 15:30
    Hello Aaron, 

    Because the drastic change happens at lower tank levels and higher temperatures, and a vortex breaker did not correct, I recommend evaluating the Net Positive Suction Head required for this pump.  Obtain this value from manufacturer, in feet of fluid being pumped.  Next, determine the Net Positive Suction Head available during your operating conditions.

    To maintain prime in a common centrifugal pump, the NPSH Available must exceed NPSH Required. When it does not, fluid in the suction & impeller will vaporize, and performance deteriorates with cavitation.  Unfortunately, this one as reliable as gravity.

    From memory, with personal notations: 

    the basic equation for determining Available NPSH is: NPSHA  = Hs + Hh - Hf - Hv.   

    Hs is absolute pressure at supply tank liquid surface, in feet.  If tank is vented, then = 1 atmosphere, or 33'.

    Hh is static elevation difference between 1) supply tank liquid surface lowest level, and 2) the pump suction. 
    This number scales with relative physical brewery size, may range from 1' - 20'.

    Hf is dynamic, frictional head loss in suction piping between supply tank and pump suction.  In properly designed & maintained systems, this is small, i.e., 4'.    Frictional losses increase with flow rate.   Hf is impacted when suction piping is modified, or obstructed.

    Hv ,,absolute Vapor pressure of water. At 170 deg F, is 14'.   An aspect of higher temperature fluids working against our pumping interests. 

    a hypothetical example:

    NPSHA   = Hs + Hh - Hf - Hv
    NPSHA    = 33' + 2' - 5' - 14' = 16'   Hence, Pump Manufacturer Requirement, NPSHR should be less than 16'.


    Many, MANY problems in brewery pumping systems involve NPSH.
    Centrifugal pump manufacturers offer helpful references to explain the hydraulics involved in this critical assessment, which should always be done during design phase. And your local equipment representative should be qualified to assist with the analysis.
     
    Good hunting, 

    David






    ------------------------------
    David Ammons, PE
    Brewing Process Engineer, Retired
    Saint Louis MO

    ammfamd2@gmail.com
    ------------------------------



  • 8.  RE: Hot liquor pump pressure loss

    Posted 12-13-2022 14:47
    Thanks for the ideas everyone! NPSH definitely seems to be the issue here, and I've attached the curve for my pump below, and some images of the piping to the pump. Some additional information to your responses:

    1. The pump becomes quiet and begins rattling when this happens, indicating cavitation as Dan mentioned.
    2. The run of pipe from the tank outlet to pump inlet is a 15 foot pipe with 4 curves in it! This is a great amount of distance and bends, but how the brewhouse was built from the manufacturer. During the first few months of operation here, there were no issues at all during sparge. This condition just appeared one day, which is even more unusual as nothing has changed at all. 
    3. I do regular acid cycles through the HX and loop, and have inspected the pump and piping for any scale buildup. 

    The long term solution here seems to move the pump closer to the HLT and eliminate the bends in the piping. I'm also going to try and top off the HLT after mash in to see if the increased water volume eliminates the issue. 

    Thanks again everyone, will keep you posted if I make any progress here, and please feel free to add any additional feedback you have.

    ------------------------------
    Aaron Dahl
    Golden Age Beer
    Homestead PA
    ------------------------------



  • 9.  RE: Hot liquor pump pressure loss

    Posted 12-13-2022 18:27
    Edited by Walter Heeb 12-14-2022 10:44
    Hi Aaron,

    Here are a few things that may help you in pursuit of solving your NPSH issue:

    1. Here is a link to a Grundfos document with pump curves for their range of pumps.  Looks like most of these have 2-3 meters of required NPSH.
    2. Follow this link to see a recent fluid dynamics presentation from the District Great Plains 11/22 meeting in Lawrence, KS.  There is an online calculator referenced on page 40 that will make calculating your NPSH available a bit easier (click here to go to calculator).

    Cheers!

    ------------------------------

    Ashton Lewis
    Manager of Training and Technical Support
    BSG Craftbrewing
    MBAA District Great Plains, Technical Chair
    Springfield, Missouri
    (417) 830-2337
    ------------------------------



  • 10.  RE: Hot liquor pump pressure loss

    Posted 12-14-2022 16:15
    Hi Aaron,

    Sounds like a lot of good advice already. Just wanted to add that we occasionally get cavitation issues on our HLT pump but it's more often related to temp of the hot liquor. Our best guess is at higher temps we're seeing some bubbles come thru from boiling at the bottom steam jacket while steam is on. A short burst of cold water thru the top (as we would normally fill it) seems to stop the issue and corroborate our suspicion here. 

    Rob

    ------------------------------
    Rob Schwarz
    Head Brewer
    Storm Peak Brewing
    Steamboat Springs CO
    (310) 940-7816
    ------------------------------



  • 11.  RE: Hot liquor pump pressure loss

    Posted 12-15-2022 11:33
    Have tried running a test sparge with full hot liquor volume and 170 F water temp? I would try that to see if it relates more to volume or temperature.

    Any chance there's a blockage of some kind in the pipe that supplies water to the pump? A gasket, hard water scale accumulation, perhaps another object?

    Is this a problem that just cropped up several months ago? How long had you been operating this system before the problem arose?



    Dave Chichura
    Ex Novo Brewing
    Corrales, NM




    Original Message


  • 12.  RE: Hot liquor pump pressure loss

    Posted 12-16-2022 16:39
    Hey Dave,

    I had the same thought, and ran this test today actually. Even with a completely full HLT, the pump began to lose pressure in the exact same behavior. I've inspected the pipe for any obtrusion or scale, and didn't find anything. 

    I brewed here for several months before this issue arose, and nothing has changed in my setup during that time. Will keep hunting.....

    ------------------------------
    Aaron Dahl
    Golden Age Beer
    Homestead PA
    ------------------------------

    Original Message


  • 13.  RE: Hot liquor pump pressure loss

    Posted 12-16-2022 16:59
    Hi Aaron,


    If this started randomly and everything used to work, I'd change the pump seal and see if that helps. Also look for failing gaskets in the header pipe or ways you could be sucking in a bit of air and starving your pump.

    Cheers
    Joe



    Original Message


  • 14.  RE: Hot liquor pump pressure loss

    Posted 12-17-2022 07:32
    Hi Aaron,

    Per my previous response with troubleshooting steps. Since this developed over time, if you haven't already done a thorough inspection of the pump internals, I recommend disassembling the pump and inspecting the clearances in the impeller and casing, looking for scaling or blockage in the pump impeller and flowpath, and replacing any worn parts before doing anything to piping or other hardware.

    Harlan Coomes
    Dipl.Brew





    Original Message


  • 15.  RE: Hot liquor pump pressure loss

    Posted 12-17-2022 11:56
    Hi Aaron
    If it worked before and there is now no obstruction and all seals look ok, my last idea is to check the calibration of the HLT temperature and level transmitters. There's an outside chance that one is now out of calibration so that water level is lower than before or temperature is higher?
    Regards 
    Dan Carey 
    New Glarus Brewing



    Original Message


Related Content