[Vwdiesel] Hydraulics and heat: was,

[James Hansen]

Okay.
I'm no engineer, but I'm willing to bet that the heat comes from EVERYWHERE
with in the pump. You are both right.  sort of, I think Lee is more right
however. The whole point of recirculating the fuel is to do a couplea
things.  Cool and lubricate the injectors, and cool and lubricate the
pump... sooooooo I don't think I would be wrong in thinking that the major
contributor to the fuel getting warm is friction.  Just where that friction
comes from... some from the bearing surfaces, some from the weights, and
some from the piston pump leakage.

Now it takes very little leakage from a high pressure fluid to generate an
enormous amount of heat (you should have been there to see when the oil
smoke when the hydro drive went out on my combine...), but if the pistons
leaked THAT much, they would tend to erode, which has been my experience
with variable volume hydraulic pumps, the hydrostatic drive units that
propel some farm equipment. There is planned leakage that serves to cool and
lube, but I doubt that the severely retentive engineer type back in the
fatherland didn't plan for that exactly, down to the millilitre per hour.

Weights sloshing in a non-viscous homogenous fluid tend to require little
horsepower, so very little work is actually accomplished, hence little heat.
Were there to be a resistance, such as the weights pumped the fluid as well
against pressure, then yes the opportunity to heat the fuel would be higher,
but not if the weights are not pushing against a resistance of some
significance. The fuel is just spinning around inside the pump housing with
the weights the way it is now.


So there, you have the farmer approach that started as a couple of words and
I babble on into paragraphs...
-James
---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.721 / Virus Database: 477 - Release Date: 7/16/2004