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Formula for head

[Deleted User]
[Deleted User] Posts: 0
in THE MAIN WALL
Can I use the formula Longest run in feet. Add 50%. Times .04. to find the feet of head . Will this work on any size pipe. Isn"t the head greater on smaller tubing?

Comments

  • Geo_2
    Geo_2 Member Posts: 76
    head

    Or just divide the longest loop by 16.6.
  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    huh??

    Fred,

    Sorry to be pendantic, but loops don't have head. Pumps have head as they try to force water through the pipe, which present hydraulic resistance. The most critical factor is the flow rate in feet per second, so without knowing the flow you can't know the required pump head. There are secondary effects of larger pipes having lower surface to volume ratios and surface roughness of the pipe as well.

    I use Siggy's program to work all this out, it's great when someone else does my homework. :)

    jerry
  • ernie_3
    ernie_3 Member Posts: 191
    all this time...

    and to think all this time I thought the formula was dinner and drinks.......:) Sorry, couldn't resist!
  • Tony Conner
    Tony Conner Member Posts: 549
    Pipe Vs Pump

    Smaller pipe or tube will have a bigger pressure drop than large tube, when carrying the same GPM. This is often the trade-off that is made when designing systems. Smaller pipe is cheaper to install, but more expensive to run, as you'll need more pump horsepower to move the same GPM. Or you can flip it the other way, and have a more expensive piping installation with larger pipe, but now the resistance is lower for the same GPM, so you can run a smaller pump motor.
  • Mike Kraft_2
    Mike Kraft_2 Member Posts: 398
    Finding Head

    :).........Best thing to do is establish the GPM.To do this you need to have a heat loss.Then BTU/500/∆T =GPM.Now you measure your longest zone,loop or branch of your distribution.Rule of thumb is to divide this in half and add to your run total.This covers you for all the fittings and valves.Then you need a chart to reference the size of your piping on this system.This will give you a multiplier to your original query of head.

    If you are designing a new system you will need to be alert to the velocity of the fluid.This will determine the size of your distribution piping.4'/sec. is as high as this # will want to be.The reason for this is to avoid velocity noise through your distribution.

    When sizing one pump for multiple zones you will need to accumulate the overall flow rates to establish the correct pump for your install.But not the head or friction loss through them.ONLY the longest run.

    cheese
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