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How to verify flow value

Brian_18 Member Posts: 94
Nice set-up Hot Rod!

And others, Thanks for verifying this. I looked around the various pump manufacturers sites, but didn't come up with a tech paper for this. (probably are there, just didn't see immediately) I have a few high accuracy filled gauges kicking around (just have to find them). I suspect this loop is near (or over) the end of the pump curve for the size I have currently installed. It's a new pump by the way. So, pinpointing actual flow to the n'th degree is not my goal. In the end, I suspect I need to change the pump to a higher head model, but really want to know why, as my calculations usually have good results. In other words, I need to satisfy my own curiosity (by George). Anybody know how to factor in Glycol % ?? Thanks for the help


  • Brian_18
    Brian_18 Member Posts: 94
    It seems to me...

    That I can quantify actual flow by using published pump flow curve and taking a pressure reading at the pump (supply side). I have an underperforming zone, which some of the (existing) piping is burried in structure. I tried to estimate what's in there, but maybe I under estimated (unseen) head loss. Without getting into expensive ultrasonic gadgets, I would think the pressure plotted against the pump curve would get me pretty close.

    Is this method valid? Accurate enough?
    I assume I must measure differential pressure? (observed pressure minus static system pressure)
    Do I make any adjustments for glycol?

    Thanks in advance
  • Rich Corcoran_34
    Rich Corcoran_34 Member Posts: 1
    Checking flow

    using the actual pump performance is a great diagnostic tool.

    You will need to know the diffeential pressure accross the pump. Once you know this value, convert psi to feet of head (psi x 2.31) and plot the point on the pump curve that corresponds to the pressure gain at the pump. You will then know the flow.

  • Brad White_9
    Brad White_9 Member Posts: 2,440
    I generally agree with Rich

    but (you knew that was coming, didn't you? :) ) the pump curve as flow predictor is only as accurate as the pump's manufacturing tolerances. Flow could be +/- 10 percent, say 0.5 GPM over a 5 gpm pump.

    Joe at Taco may have more insight on this than I do. Any over-statement of accuracy is just a guess based in field experience and factors outside of manufacturer's control.

    Impeller wear, age of the pump, lots of things factor in. Accepting this though, it may be close enough for what purpose you are using the information.

    Smaller pumps tend to vary more than larger ones. Small pressure differentials and system effects may exaggerate your readings. How accurate a gauge you use is key. Digital is my choice.

    So I would accept at fact value what Rich suggests, it is as good as any method (with a good gauge) so long as you accept the limitations of manufacturer's tolerances.

    If you want more accuracy and know the emission rate of your radiation or coils at steady-state, you can use temperature difference to corroborate. Of course, this may be exactly the information you are trying to calculate in the first place!

    And yes, you have to correct for glycol. That can throw things away from the curve rapidly especially if at different temperatures. And no, you do not have to deal with subtracting the static pressure in a closed system. One side cancels out the other.

    One other tip: If you can accurately measure the amperage and your curve has a HP or Wattage curve, you can further triangulate the operating point on the curve.
  • hr
    hr Member Posts: 6,106
    Use the same gauge

    if you can to eliminte the error between multiple gauges. Here is a deal I made for that purpose.

    hot rod

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • John Starcher_4
    John Starcher_4 Member Posts: 794
    I have yet to find.....

    ...a manufacturer's pump curve that shows wattage or amperage.

    Where do you find these????

  • Brad White_9
    Brad White_9 Member Posts: 2,440
    More on commercial pumps

    B&G, Taco and others have brake horsepower curves plotted on the same basis as the flow/head curves. Sometimes you can get them from manufacturers if not published for public information. All manufacturers strive to have low wire to water efficiencies. They know the data but just may not publish it because it is only of peculiar interest to engineer types. :)

    With most water-lubricated circulators we are talking about, it is all Watts and very few amps anyway. Just one facet of corroboration to be used if available.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Good Call Hot Rod

    That corroborates what my Dad always says:

    "A man with one watch knows what time it is. A man with two watches can never be sure."
This discussion has been closed.