I  am not  an engineer but does anyone know why the fuel pressure  regulator
on a car  engine is installed at or close to the fuel  rail?


Wouldn't  it be easier to pressurize the fuel  rail like they pressurize
any
hydraulic  system, with  the pressure regulator
installed right at the pump? That way   we would not need a fuel return
line?

I appreciate  your comments.  Thanks.


It has to do with the return line system. Fuel   is constantly recirculated
to keep it cool I think. Keeps the air  bubbles  out which would cause a
miss.


Paul  Lamar


It is just like screwing the fuel  pressure  regulator into the side of a
carburetor. The regulator  provides  accurate pressure where it is needed
and
absent any additional inputs like  heat or flow dynamics. Same for  the
fuel
pressure sender.
Lynn E.  Hanover


Hi Ramon,
I too am not an engineer. A beer powered  grease monkey
would be more accurate hehe.
The regulator is positioned  after the fuel rail to maintain
the selected fuel pressure inside the fuel  rail. The pump may
produce lets say 100psi, if you block off the return  line, the rail
and fuel line will see 100psi. (give or take a bit for the  additional
inputs that Lynn mentions). Put a regulator after the rail and  it
will dump off a proportion of the 100psi into the return  line,
bringing the fuel pressure at the rail down to the psi the  injectors
are rated to handle.

A 13b with flight related loadings,  uses approximately 14 gallons
per hour at 75% power lets say. The high  pressure injector fuel
pump might give more than 200 gph. That extra 182  gallons
must go somewhere. Back to the tanks is the favoured option.
If  you block the return then two things will happen, as above
the pressure at  the injectors will be too high. And, the fuel
pump will be pumping against  a brick wall, working much harder
than its intended duty cycle. At idle  fuel consumption may be
only .5gph or less, a small percentage of the pumps  intended
capacity. With not enough fuel circulating through it to  help
keep it cool(as Paul mentions), it will overheat and rather
quickly  die. Pump in tank will keep it cooler. Warning,
overheating pump in tank  with possible short circuit may
cause a harmfull backside warming effect.  Thankfully a very
rare occurrence when the fuel system is properly  designed.

Diaphragm type pumps are designed to build up and  maintain,
usually low pressure, in the line. If a return is incorrectly  provided
for these pumps, pressure will again dump off there. They  will
pump constantly instead of pulsing fuel up the line only when  its
required, and wear or burn out prematurely also. As far as I  know
there are no high pressure injection diaphragm pumps about.

Sam  Watson

Unlike hydrogen gasoline will ignite over a relatively  narrow
range of mixtures. 10:1 to about 18:1. The tank environment  is
always too rich to ignite the mixture.

Paul Lamar

Ramon
Note that the relief valve is at the far end of the rail from the supply
connection. This is to assure that all of the injectors see the exact same
fuel  pressure. With the relief valve at the pump, each injector would see
various  pressures as adjacent injectors open, venting small volumes and
pressure. Same  exact thing as Mazda's oiling system. The relief valve at the very
end of the  system provides uniform pressures for each
device along the system. Most cars have that relief valve in the  pump,
and as a result the further from the pump each device is located, the lower
the oil pressure available for that device.
Lynn E. Hanover