Air in Fuel Return Line
in 912iS Technical Questions
8 years ago
Hi All
Not sure if anyone can help me here, but I thought I would see.. I am about to start my engine this coming weekend and we are just doing some final testing of the fuel system.
Yesterday, we ran some fuel through the system - from the tanks through the engine, then into a fuel container (instead of back to the wings). We connected some temporary clear hose to the outlet just after the regulator (where the fuel would normally begin the return to the tanks).
As it was clear hose, we could see into the hose - at all times with the fuel pumps operating, there was a constant stream of what looked like air bubbles in the flow. There are no leaks in all the fuel connections (aluminium and stainless steel lines throughout).
We tested a few points in the system to make sure there were no points of entry for air.
Question - is this normal? Has anyone see this?
One possibility we though of is that the fuel is coming from the rail at 45psi, then exiting the regulator (which is at ambient pressure), so there may be a rapid expansion of gases/vapor at this point? Or the regulator may be creating the stream of air in the return line somehow. We concluded that this is probably normal, but just thought I would check to see if anyone has made the same observation or may know what's happening.
Thanks,
Ian
Not sure if anyone can help me here, but I thought I would see.. I am about to start my engine this coming weekend and we are just doing some final testing of the fuel system.
Yesterday, we ran some fuel through the system - from the tanks through the engine, then into a fuel container (instead of back to the wings). We connected some temporary clear hose to the outlet just after the regulator (where the fuel would normally begin the return to the tanks).
As it was clear hose, we could see into the hose - at all times with the fuel pumps operating, there was a constant stream of what looked like air bubbles in the flow. There are no leaks in all the fuel connections (aluminium and stainless steel lines throughout).
We tested a few points in the system to make sure there were no points of entry for air.
Question - is this normal? Has anyone see this?
One possibility we though of is that the fuel is coming from the rail at 45psi, then exiting the regulator (which is at ambient pressure), so there may be a rapid expansion of gases/vapor at this point? Or the regulator may be creating the stream of air in the return line somehow. We concluded that this is probably normal, but just thought I would check to see if anyone has made the same observation or may know what's happening.
Thanks,
Ian
