If a NRV or PRV is in the system to bleed off excess pressure when the boost pumps are operating, it would not be an external leak when it is working correctly as it is doing the job it is designed for, depending on the pressure it is set at. But if the valve is not seating as it should air can be drawn in from the return line.
Last edited by Oldlae; 10th Jun 2008 at 08:45.