Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

Formula for GPM

zepfan
zepfan Member Posts: 315
Is there a formula to determine pump gpm, when the pump curve is not available? Something other then a stopwatch, and a bucket? We have a extremely old pump that the manufacturer is un known. No nameplate
Thanks to all.

Comments

  • ratio
    ratio Member Posts: 2,918
    You can make a guess by looking at the pipe size, connected load, ΔT, etc., but aside from a true measurement, I think you're outta luck.

    Post a pic, someone may recognize it.

    Zmanzepfan
  • Zman
    Zman Member Posts: 6,967
    ratio said:

    You can make a guess by looking at the pipe size, connected load, ΔT, etc., but aside from a true measurement, I think you're outta luck.

    Post a pic, someone may recognize it.

    This is a good idea in any event. There is no saying it was sized correctly to begin with.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    zepfan
  • Ironman
    Ironman Member Posts: 6,555
    If you know the btus it's carrying, and the delta T, then use the universal hydronic formula: btus / (delta T X 500) = gpm.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    zepfan
  • hot_rod
    hot_rod Member Posts: 15,014
    Depending on how accurately, or how badly you want to know :)
    You can rent ultrasonic flow meters, they clamp on the outside of the pipe.
    Motor HP size, rpm, diameter could get you a close estimate.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    zepfan
  • zepfan
    zepfan Member Posts: 315
    Thanks to all. I was using the delta td x 500. And will try and get a picture
  • Tim_D
    Tim_D Member Posts: 44
    Do it right. Figure out the connected load, BTU's required. Once this is known you can calculate the required flow. Once you have the correct flow you will need to figure out the friction loss through the piping and heat emitters, plenty of rules of thumb and charts to help with this. Once you have the required flow and a good idea of the friction loss it is easy to select the correct circulator.
  • Zman
    Zman Member Posts: 6,967
    If you get to the point where you are looking for a decent SWAG and the load is unknown, plug in the GPM for the pipe size at 4ft/sec and use a delta T of 20. For example 1" copper carries 10.9 GPM at 4 ft/sec. 10.9 (gpm) x 500 (constant) x 20 (delta) =100,900 btu/hr. I have found that the majority of engineers design this way. In some cases, you can check a known part of the original design to verify the original engineer's preference and then apply the formula to the unknown portion.
    http://s3.supplyhouse.com/product_category_files/11448-Flow-Rate-Chart.pdf
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    zepfan
  • Henry
    Henry Member Posts: 988
    Do it the simple way that works. Get a B&G System Sizer dial. By turning the dial to the approximate net BTUs ( you may do a combustion test, new condensing boilers have the Delta T and combustion rate) plus the Delta T will show you the GPM. No math and I have used it in many litigations.
    zepfan
  • hot_rod
    hot_rod Member Posts: 15,014
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    zepfan