Using a 340LPH in tank transfer pump to 2 450LPH surge tank pumps I cannot get the 515 regulator to set fuel pressure lower than 75PSI. The adjustment is completely maxed to lower the pressure but I still cant get lower than 75PSI. Is this regulator just not capable of controlling the pressure or is there another issue?
This is assuming you’ve verified that your gauge is not the problem…..
You’re either overrunning the regulator (meaning it’s undersized for your application) or there’s a restriction in the return line. If you’re running both of those pumps full time, you’re most likely overrunning the regulator (assuming it’s a standard seat 515 series. If the pressure is still too high with only one pump running there’s a restriction in the return line. Said restriction could either be a line that’s too small, too many bends (especially via the cheap drilled 90*’s rather than pipe bends), or a vent line that’s too small between the surge tank and main tank and/or the main tank and atmosphere.