I have a few Scania 164's (DC1602 and DC 1601 engines) and all I mean by "low" is that it is lower than the actual pressure that the injectors discharge at. Obviously for it to work the "low" pressure is alot higher than the pressure of lets say the DSC 1413 and DSC 1415 that my older 144's engines use as a supply to the mechanical pump.

EDIT: 144 is the same truck, Scania 4 series but with a 14 liter engine, Euro 2