Some questions about fuel fump

[Markthejunior]

Hi, everyone. I have some questions about selecting fuel pumps. What is the shut off pressure of fuel pump? And can a pump produces higher pressure fuel than the pressure mark on it?
Like , a Bosch pump, 3bar, and does this mean the maxium pressure it can produce is 3 bar or can it produce, say, 4 or 5bar?

[Markus]

You will find the shut off pressure of a pump (if it has one versus a safety pressure valving) in the fuel pump's data sheet. And you'll find the data sheet when you start searching for it. Product number or name is usually sufficient information.

Bosch pumps (at least the motorsport ones) usually state the maximum operating pressure which can but should not be exceeded. For example the FP100, smallest of the Bosch Motorsport pumps, is rated for max 5 bars but has the safety valve set at 7-12 bars.

[Markthejunior]

Thanks for answering my questiones.
And i search for some information and get something like this, the pressure in the techniques sheet of this fuel pump is 4 bar, and what the 4bar means? The maximum pressure of fuel it can produce ? Or most of the time the pump should work around 4 bar? And the shutt-off pressure is the pressure that opens the safty valve?Sorry if i have too many questions, i just really can't smooth this thing out.
Techniques:SHUTT-OFF PRESSURE 6BAR
WIDE OPENFLOW 150L/H
VOLTS 12V
PRESSURE 4.0 BAR
Interchange:
VDO:405 052 003 001, 405 052 003 002
V.W:8AO 906 091 A8AO 906 091 G PIERBURG:7.18259.50.0
BOSCH:0580 453 070,0580 453 071

[Jay Lawrence]

From the information you have given, yes, it appears that the normal operating pressure is 4 bar, and the shut off pressure (6 bar) will be the safety valve or some other override.

The purpose of the pump is to send constant pressure to your fuel rail, which then (through your injectors) regulates fuel flow. Although there are some pumps that can regulate flow directly, it sounds like your's is designed for constant pressure delivery

[Markus]

In the case of the pump you described I'd say 4 bars is the intended maximum operating pressure. Datasheets don't necessarily state a minimum operating pressure but might have some indications to it (charasteristic charts). You don't want to get too close to shut-off pressure.
I would match the fuel pressure to what the injectors were designed for - if that information is available.

Please note that in your case the fuel pump flow is rated to non-pressurized output and it reduces drastically when pressure is added and raised. Always check the flow pressure rating!

Example: Bosch FP100
Flow at 2 bars & 12V: ~145l/h
Flow at 6 bars & 12V: ~65l/h
My estimation for free flow at 12V: ~165l/h

My wild educated guess for the pump you describe would be ~100l/h at 4 bars & 12V.