Hi,

For pressurized fuel systems, flow reynolds numbers must remain below 5000 and velocities under 1.35 fps.

Fuel pressure losses in round tubing at low vapor-liquid ratios may be computed by the following relationship:

 delta P = 3.417 x 10(-5) x u(0.25)l P(0.75)v(1.75)/d(1.25)
 
            all X (1-V/L)

Where:  u = viscosity, English units (centipoise x 0.000672)
        l = Length of pipe, ft.
        p = Density of fluid (lbs/cu ft)
        v = Mean velocity of fluid, fps
        d = Inside diameter of pipe, ft.
      V/L = Vapor liquid ratio, dimensionless
  delta P = Pressure drop, psi

Note: Numbers in parenthesis are powers i.e. 10(-5) = ten   to the minus five power.

Hello again,

I forgot to preface my remarks to indicate that the reynolds number and velocity are recommended design practice for general aviation piston aircraft fuel systems.

Thanks mate, have a good one.