Diesel fuel filter question

[Pete7]

Can anyone explain why this fuel filter off a ford 1620 would have 2 lines coming from the tank? In the picture I took the line off that comes from the tank ( barb is visible). The other line goes back to the top of the tank. There is of course a 3rd line at the fuel filter that goes to the pump.
But 2 lines from the tank? Overflow or venting?

 

[Dieseltech]

Can anyone explain why this fuel filter off a ford 1620 would have 2 lines coming from the tank? In the picture I took the line off that comes from the tank ( barb is visible). The other line goes back to the top of the tank. There is of course a 3rd line at the fuel filter that goes to the pump.
But 2 lines from the tank? Overflow or venting?

Probably an air bleed line to help keep air out of the filter BEFORE it can get into the injection pump.

 

[Pete7]

Probably an air bleed line to help keep air out of the filter BEFORE it can get into the injection pump.

Thanks, Dieseltech. I’m new to diesels, always gas up to now. I did notice the filter bowl filled with fuel fast and easy compared to a sediment bowl on a gas engine. Being vented by that line would explain it and I can understand how it would also help bleed the air out.