[Vwdiesel] Pump pressures, banjo jet sizes and injector leakage...

[Mark Shepherd]

Sandy says...

I think the way Hagar did it was to use a bolt long enough
to accomodate 2
banjoes (?)
 One was an input type, open free flow, to which he attached
the guage, and
the other was the output "metering" banjo with the tiny
hole.

The transfer pump is capable of much more volume than the
tiny hole can
pass, and the pressure inside the pump is controled by a
spring loaded ball
relief valve on the top at the sprocket end of the pump that
allows the
excess fuel to recirculate back around the transfer pump
(the vane pump) ,
maintaining a constant pump internal pressure, not much
affected by speed.
There is some pressure change with speed change, , and that
is used to
operate the timing advance, but I don't think it's affected
by the small
size of the hole in the return banjo.

On my Quantum there is only one banjo with two outlets.. but
the hole that I felt was causing 'back pressure was the one
in the bolt.. it may be only a 1/4 mm or less diameter and
so maybe a 1/10th of the 'injector' return hole and 1/100th
of the main return hole thus making those banjo holes seem
relatively unrestricting. I'd like t oknoew what the hole
size in Hagars extended bolt is!
I'm purely guessing here but surely if this bolt hole is too
big then fuel will rather leave the pump than open this ball
valve path of least resistance or what-not
Miser

Hey Andrew
 I was wondering why I can only get 50mpg US on a run I look
forward to getting a more economic Quantum in the future
(80P)