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    Topic: Condensate Pump Cavitation
    yefim
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    Condensate Pump Cavitation
    on: April 30, 2015, 11:50

    Our plant is experiencing severe audible cavitation at the condensate pumps with extensive damage of the 1st stage impellers. The ACC condensate collection tank is 20’ above the pump elevation, suction piping is adequately designed and NPSHR is well satisfied. The pumps are Weir Duoglide 2-stage horizontal centrifugal pumps. Hydraulically, we can’t find any reasons why those pumps would cavitate. The pumps are somewhat oversized, but still operate above the manufacturer’s minimum flow requirements. I wonder if any other ACC users have similar condensate pump arrangement and if anyone experiencing similar problems. I would greatly appreciate any inputs.


    danny7143
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    Re: Condensate Pump Cavitation
    on: April 30, 2015, 14:44

    What is your Condensate temperature? if the temperature is close to saturation the fluid may flashing to steam at the pump.


    davefitz
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    Re: Condensate Pump Cavitation
    on: April 30, 2015, 16:30

    There can be an inlet nozzle vortex at the bottom the condensate tank, unless the EPC had provided an anti vortex baffle at that nozzle. This can reduce NPSH by 2-10 ft.


    Also, if there is a tee in the piping ( one downcomer to 2 pumps) then there can be a large loss of NPSH at the tee. A better design is one downcomer for each pump.


    Inreasing the diameter of the downcomer and adding an inlet vortex breaker at the tank nozzle that feeds the downcomer should solve the issue


    BSME and MSME from Rensselear Polytechnic Institute (RPI) .

    Instructor of thermodynamics at RPI

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    Super Dave
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    Re: Condensate Pump Cavitation
    on: April 30, 2015, 17:51

    Several things to think about. First, I will ask do the pumps share a common suction line? Does the line TEE from the tank splitting into two lines? Does your piping system have a return line from the pumps back up to the condensate tank?


    Two pumps sharing a common suction line in a system that has vacuum will create issues between the two pumps, especially if they are running at the same time.


    Each pump will fight the other for flow causing or could cause shuttling or axial movement on the pump shaft. The axial movement will take out bearings and mechanical seals.


    Some systems have a return line which runs from the pump or from the discharge section of the piping up to the condensate tank. While under a vacuum still, the line aliveiates suction issues causing cavitation or shuttling of the pump shaft axially.


    I also wonder how many nineties and tees are in the piping system to the pumps and from the pumps? The more bends in the piping the more fluid turbulence will be working against the pump. Flow straighteners do not always work well and in some cases the turbulence in the fluid will cause the flow straighteners to break apart and cause other pump problems.


    You never mention either if you have built in strainers in the suction piping. Strainers are nice unless they are not regularly checked for material build up. You could have a plugged strainer in the system causing flow issues, forcing the pumps to over work as they try to maintain flow. Some strainers are for start up only, and should be removed once the system has cleaned up. The strainers could be causing flow issues even though they are clear too.


    Maintenance Specialist for NV Energy at Walter M Higgins III Generating Station South of Las Vegas NV.

    Experience includes machinist, millwright, mechanice, welder and general industrial maintenance for over thirty years.

    Omiponle
    Member
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    Re: Condensate Pump Cavitation
    on: May 3, 2015, 12:31

    First things first!

    Some history of the performance of the pumps will be necessary to x-ray this problem.

    How old is the plant and for how long has this problem been? If the problem is as old as the plant, then it is likely to be a design issue. In this case you will need to review the entire hydraulic design. However, if the problem started recently, or some time after plant commissioning, then it is necessary to take a close look at all the events leading to the beginning of the problem. Some quick checks have already been mentioned – strainers at pump suction and temperature of the condensate.


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