1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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?

  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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook