[Vwdiesel] Mileage test 84 Rabbit. --- ( hagars Pickle Jar day ? )

[Lee Hillsgrove]

>Like I stated long time ago  ---- flyweights trashing around in oil is a
power waste.
>And it is.   Fuel in jar gets very hot.


  I stand by my theory that almost all of the heat is generated by the high
pressure diesel fuel leaking (and intentionally spilling past the collar)
from the high pressure section back to the low pressure in the pump body. It
takes power to pressurize the diesel fuel, and if it is allowed to vent back
to a low pressure area without doing any work, that energy is then released
as heat.
 I have seen this firsthand with the Rexroth axial piston hydraulic pumps
that were used to power molding presses where I used to work. The main
hydraulic reservoir would run between 120 and 130 degrees, but the case
drain line from the pump body would be uncomfortably hot on a new pump and
so hot it would burn you immediately on a worn-out pump with lots of leakage
past the pistons or swashplate. This was further backed up by the amp draw
on the electric motor - a worn pump would draw more amps than it should and
would actually overload and trip out the motor if it got bad enough. Why?
For a given amount of power input (amps) you can have high pressure and low
flow, or low pressure and high flow, but you cannot get both high pressure
AND high flow at the same time. With a new pump running at 2000 psi, the
power required to get full speed and pressure was matched to the electric
motor driving it. Once the internals got worn and the case drain started to
pass more and more oil, the motor was now being asked to deliver the same
2000 psi AND produce a high volume of oil out the case drain line.
 One other valuable tip I learned from working with hydraulic systems is
that if you suspect you have a high pressure internal leak in some component
in the system but do not know which one is leaking, you can do one of two
things very easily to pinpoint the problem; if it is quiet enough, you can
often hear the leak. It will sound like a compressed air leak. The other
thing you can do is to allow the system to run for a short period of time
and use your hands or a pyrometer to locate the hottest component, that will
be where the leak from high pressure to low pressure is.

 I don't deny that the flyweights spinning around in the fuel will
contribute some heat, but I maintain that it contributes only a fraction of
the total heat produced. Almost all of the heat found in the fuel flowing
through the return line from the case of the pump comes from the leakage of
pressurized fuel to a low pressure area.


  Lee
  Oo-v-oO
  PP-ASEL
  KB1GNI