Haltech F10 - Manual (Page 96)

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Since the pressure regulator operates on a return system, there should always be fuel being
returned to the tank, even when fuel flow to the engine has reached its maximum. If this fails
to happen, the fuel pressure will fall out of regulation. Therefore the fuel pump must be
capable of delivering significantly more fuel than the engine is going to use. As a guide, the
pump should flow 30% more fuel than consumed by the engine.
If you cannot achieve the required fuel flow from one pump, you can employ two pumps in
parallel.
If you choose to use a low pressure pump to augment the fuel flow of a high pressure pump,
place a check valve after the low pressure pump and before the high pressure pump to prevent
an overpressure condition at the output of the low pressure pump.
C.5 Fuel Rails and Pressure Regulators
A long fuel rail with narrow internal diameter will result in fuel pressure oscillations in the
fuel rail. The internal rail diameter should be around 12mm (½"). Even so, oscillations may
occur, particularly if the injectors are large. A fuel damper can help in removing these
oscillations. If running a multipoint set-up, batch fire injection will also reduce oscillation
amplitude. Oscillations may occur only within a certain rpm range, so a fuel pressure meter
should be monitored across the range of the engine speed and load to detect such problems.
On V configuration engines, it may be more practical to employ two regulators, one on each
bank's rail. The fuel from the pump can be split to the two rails, and the return line from the
two regulators can be joined. Since pressure regulators work within certain flow limits, this
may also save having to purchase an expensive high pressure / high flow regulator.