IO-540 Fuel Line Question

[UnPossible]

Hey - I working away on the FWF portion of my RV-10 build and have a quick question.... It looks like the fuel line from the wings to the fire wall to the engine driven fuel pump to the fuel servo is all 3/8" fuel line with AN6 fittings.

However, coming out of the servo going up the the spider is what looks like 1/4" fuel line with AN4 fittings.... why is the fuel line between the servo and the spider smaller than the rest of the fuel lines in the fuel system?

Thanks,
Jason

[togaflyer]

Can’t answer your question, but couple of suggestion. Install the fuel flow (red cube) after the Servo. Mine is installed just aft of the no.5 cylinder which avoids exposure to excessive heat. Wrap the cube with the orange fire resistance material. Fuel lines FWF, eliminate any 90 degree fittings to reduce any pressure loss. I have one 45 fitting on the output on the mechanical fuel pump. Everything else is straight. This will eliminate any low fuel pressure issues.

[BobTurner]

The fuel from the tanks is being pulled, or sucked, by the pump. The smaller the line, the higher the flow velocity, the more the pressure drops (Bernoulii?s principle). You don?t want the fuel to vaporize, so larger lines/lower flow velocities are called for. Downstream of the fuel pump the fuel is under pressure, less likely to vaporize, you can use smaller lines.