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Thread: Downtime for water pump maintenance

  1. #1
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    Downtime for water pump maintenance

    I am an investor. Financial forecasts in a proposal I am considering rest on a "100 horsepower pump capable of diverting 780 gallons per minute at 290 feet of head" running continuously at 96% of its rated capacity: 24 hours per day, 365 days a year. I am not an engineer but that looks questionable to me. I would have thought it likely that some downtime would be necessary for maintenance during the course of a year.

    Is my layman's view wrong? Can all routine maintenance that might need to be done be done while the pump continues to run?

    If not, what sort of downtime might be expected? Just a ball-park figure. 1 percent? 5 percent?

    Any guidance would be gratefully received.

  2. #2
    Administrator Kelly Bramble's Avatar
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    100 HP water pump's are as common as tires on a car... Having a backup or having redundancy pumps is cheap and easy. Therefore, running 95% + of the time is not unrealistic.

    If the operation is new then one needs to be conservative in up time estimates however if this operation has history and is well managed. Ask what the up time is...

  3. #3
    Technical Fellow jboggs's Avatar
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    Any plan should include some allowance for downtime, however minimal, even if it is just to replace the running pump with a zero-time pump. Depending on how tolerant the system is for a little downtime arrangements can be made. If the system must absolutely run 100% of the time then I would recommend designing the system with a second fully operational pump already installed and piped in. A flip of a switch and a valve and the running pump becomes the stand-by pump, available for removal and servicing. The next step down from that is to have the necessary structure and equipment in place to enable a quick changeover.

    Years ago I was involved in designing a conveyor system for an overnight delivery service. When their nightly 4-hour sort starts up they absolutely cannot tolerate equipment failures. I noticed that they had what seemed to me to be an excessive number of jib boom cranes all over the place. I could see no purpose they served in the sort operation. I was told that each one was there to service a single drive motor or gearbox just in case it failed at the wrong time. In many cases the spare motor and gearbox for that one location were stored on an adjacent platform and catwalk built just for that purpose, in case they are ever needed in the middle of the night. Bottom line is that the cost to set up an operation that runs well is one thing, while the cost to set up an operation that continues to run well no matter what is another thing altogether.

  4. #4
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    Kelly

    Thanks. But it's not a case of running 95% + of the time. It has to run 100% of the time albeit at 95% + of capacity.

    There are in fact three pumps involved. But the capacity of the onward system is what restricts all three of them, if running at once, to 96% of their pumping capacity. My concern is that if one pump is down, the other two cannot make up the whole of the shortfall during the period of its downtime. So, because the three pumps together cannot exceed the capacity of the onward system, that shortfall can never be made up.

    Notwithstanding that, the financial forecast is based on the "onward system" always carrying the full amount. I appreciate that a fourth pump would solve that problem, but there is no fourth pump included in the proposal.

    The particular operation is new. Although my understanding is that the operator has considerable experience elsewhere, I am not aware of it facing the same "onward capacity" constraint in any other situation.

    I do intend to ask them about it. But I'd like to ensure that, before I do so, I have a sufficient feel for the topic as not to be blinded with science. Hence my original question.

  5. #5
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    jboggs

    Thanks also

    Care to give me a ballpark figure on that "however minimal"? An hour? A day? And is that per week? per month? per year?

    Sorry but I'm an innocent abroad here.

  6. #6
    Administrator Kelly Bramble's Avatar
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    Here’s my take – you’re a financial guy estimating cost of operations, ROI on a systems engineering configuration. Moreover, you are on an engineering website asking anonymous people for reliability information on a system that we could not possibly have a comprehensive understanding on.

    In engineering it’s called “bean counters doing engineering work or second guessing engineering”. Please don’t take my statement personal.

    You said “operator has considerable experience “– seriously, if you’re NOT comfortable with this operator’s reliability design or estimate ask for clarity from the systems engineering folks.

    Ultimately, if you are not comfortable with the “operator has considerable experience“ reliability estimate(s) and the ROI looks marginal then this is probably NOT an investment for you.
    Last edited by Kelly Bramble; 11-28-2014 at 11:17 AM. Reason: missing words

  7. #7
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    Kelly

    I take your points. And I don't take them personal.

    However, I did not originally ask "anonymous people for reliability information on a system that we could not possibly have a comprehensive understanding on". I asked a more general question to which I thought there might be a simple answer. "Can all routine maintenance that might need to be done be done while the pump continues to run?"

    My amplification into a "system" was given simply to explain the difference between "running 95% + of the time" which your answer mentioned and "It has to run 100% of the time albeit at 95% + of capacity" which was what concerned me. Your answer suggested a less than 5% downtime but I wanted to make sure that that was what you meant.

    Perhaps I am wrong in assuming that there is a simple Yes/no answer to my general question. Perhaps I am wrong in thinking that, if the answer is "no" it might be possible to suggest a ballpark figure for downtime. Perhaps I am wrong in hoping that an engineer would answer a bean counter's question.

    If so, I'll go away. But in case I am not wrong, I will remain subscribed to this thread for a little longer.

  8. #8
    Technical Fellow jboggs's Avatar
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    pps, It seems neither Kelly nor I directly addressed your specific question. Sorry about that.
    "Can all routine maintenance that might need to be done be done while the pump continues to run?"

    No.

    Speaking as one who has spent his life in the manufacturing world, more often than not "routine maintenance" on a pump means "replacement", at least temporarily while repairs are done off line.

  9. #9
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    Thanks for your help

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