These pumps do not have an internal bypass. A bypass style regulator and return line are required.
Proper fuel system engineering is critical for maximum performance.
This pump is not designed to use a standard conical seat style union in the inlet or outlet of the pump. Example: Part # AT981510ERL. Use of this style fitting will block flow and WILL lead to poor performance and pump failure. The ONLY correct fitting to use is a contoured port fitting with an O-ring seal such as :Part # AT985010ERL.