[Vwdiesel] Seeking experience or data on Petter stationary diesels

[Roger Brown]

James Hansen wrote:
> Never use
> anything that is compressible on something that is stuck. That's called an
> airgun/bomb. baaaaad.  Use incompressible fluids, grease etc, never air.
> never never never.  If it decides to spew chunks, they fly with a great
> velocity imparted by the energy contained in the compressed gas.  If you use
> grease, oil, etc, and the block completely fractures into tiny bits, the
> energy contained is tiny, and the bits drop to the floor.

When I first started working for NASA, one guy took me to see one of the hypervelocity guns they use for meteroid impact 
studies.  Basically it is a big, long, heavy steel tube, with very high pressure gas behind it.  Fires small projectiles very 
fast at targets to study the cratering damage.

Anyway, when they first built it, they did a hydro test on it, up to 10,000 psi or something like that.  Apparently some part of 
the gun failed under the test and blew apart quite spectacularly.  Folks were standing around observing the test and I think 
some were hurt, not sure about that.  Anyway, the point of being told that story was to not ignore the normally negligible 
things, like water is incompressible.  It is, just ever so slightly, and if you compress enough of it, to a high enough 
pressure, it does store a fair bit of energy.  Same thing with the steel, it also stretches and expands under the pressure.

Granted those are extreme cases and some not likely to be experienced in everyday life.  But every time someone mentions 
incompressible fluids, I recall that story.

I've not heard of the grease trick for cylinders, but had for removing things like pilot bearings stuck in flywheels.  Pump the 
back side of the bearing full of grease.  Then use a wood or brass rod the same size as the bearing ID, then hammer it into the 
center of the bearing.  The backside pressure of the grease usually pops the bearing out.

-- 
    Roger