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Finding flow rate with limited knowns

  1. Jun 7, 2012 #1
    Hello all,

    My basic problem is I'm trying to figure out what flow rate a diaphragm pump can provide through a length of pipe. I know the pump's max pressure and all the details of the pipe and the fluid (80w-90 gear oil), but can I solve this without knowing the velocity? Is there a way to solve the velocity through these (or other easily obtained) knowns?

    Thanks,
    IC
     
  2. jcsd
  3. Jun 7, 2012 #2
    yes, what is the rpm and cubic inches/rev of the pump?
     
  4. Jun 7, 2012 #3
    It's a pneumatically powered diaphragm pump, not a gear pump. The cycle rate is not constant as it depends on the media being pumped. The more viscous the media, the slower the cycle time.

    Is there not a way to calculate flow rate without velocity?
     
  5. Jun 7, 2012 #4
    Alright, I've think I'm on the right track with Poiseuille's Law. Q=[(p1-p2)(radius^4)]/[(8/pi)(viscosity)(length)]

    Change in pressure is 125psi
    radius is 0.5 inches
    viscosity is 1.4 poise (80w90 at 40 degrees C)
    length is 200 ft.

    I'm getting in the area of 16gpm. I expected much less. Can anyone double-check this??
     
  6. Jun 7, 2012 #5
    That's about 1hp, sounds about right, not sure of the formula, plenty of pipe flow calculators out there but most of the time manufacturers have a pump curve for different viscosity's.
     
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