[Vwdiesel] pump internal pressure

SLATERSFB at aol.com SLATERSFB at aol.com
Sat Feb 26 13:00:56 EST 2005

I kinda remember reading a while back in a thread that inj pump internal 
pressure is determined by the orifice in the outlet banjo.  If I recall 
also the internal pressure drops as the pump gets older detrimentally 
effecting pump timing over the whole timing advance curve.  How about making 
a special 
banjo with a fine thread set screw to adjust the orifice size in order to 
compensate somewhat for pump wear?  Possibly one could get better resolution 
adjustment running the threads at an angle.  Does any of this make sense to 
anyone?  Anyway, I'd love the refresher course on the subject, as it is a 
memory at this point.
Funny you should mention this. I have old pump here which I took apart two 
weeks ago in the evening just for curiosity. I could be wrong, but seems like 
internal pressure is first regulated by a spring loaded regulator very near the 
inlet banjo. Sort of like an oil pressure regulator in principle. But constant 
pressure would not advance timing with RPM, so I guess that is the idea of 
the pin hole in outlet banjo? This is the first pump I evr disassembled 
completely so I am sort of feeling my way along here, but it seems like the vane pump 
is way huge compared to the maximum demand at full throttle. Like overkill. My 
guess is that the spring in regulator, if some way to regulate this, would be 
the way to compensate for wear. Do these vanes ever wear out? The only wear I 
found in this pump was the four small shafts, that support the rollers that 
the cam plate rides on, were sort of pitted. Like roller bearings when they 
begin to make noise. 
Still & all this is one beautifull piece of machinery inside. My mind boggles 
when I think of what goes on in there at such precision & for so many 
millions of revolutions without failure.

Bob in NY 

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