I'm just guessing, but I would think having the pump set at 10 PSI and no regulator beyond would work at idle-part throttle. At high-WOT, the pressure would drop, very possibly go on vacuum, especially with dual fuelers. I don't actually know as I've never monitored/tested it before, just a guess. By setting the pressure higher on the pump to say 18-20PSI, and using a regulator just before, feeding the pump(s), set to 10 PSI to ensure we don't push the fuel past the hp pump seals, while also ensuring the lp pump has adequate additional pressure to keep up at high demand. The pressure beyond the regulator should not drop below 10PSI unless the pump to regulator falls below 10 PSI. This would keep a fairly constant 10PSI on the hp pump(s) regardless of fuel demand. Given the type of hp pump, I can't imagine it would matter with the low pressure side falling to single digit PSI, just as long as its positive pressure, never vacuum. But once again I'm just guessing.