Ahh, but air doesn't damp anything. In fact air is one of the most reliable
springs that there is, since it loses very little energy under compression
and returns almost 100% of that energy during expansion. The only thing
that air in the line might do is alter the frequency of the pulses
(depending on air volume), but not the overall energy in the system. The
pulses will still be there, but at a lower frequency and greater amplitude
in order to conserve energy. Those pesky Physics laws are a b!tch aren't
they. A damper, on the other hand, must convert one form of energy into
another, such as up and down motion into heat by way of fluid friction
(think shock absorber).
An accumulator is different since it not only has nitrogen (or air) to work
against, but a rubber diaphragm that has it's own spring constant and
internal friction to provide the damping. Most accumulators are not used
for damping since that's not what they are designed for. They are mostly
used for storing pressure that has been built up against that
pre-pressurized diaphragm...like in the brake booster system of a late 80's
or early 90's Jag or some Saab's.
It's important to not confuse a single impulse force compression, like in
those water system air chambers that prevent water hammer, to something that
has a frequency dependent impulse input like an oil pressure gauge.
Cheers,
Chris
BJ8
> Hi Chris,
>
> After the car has been sitting for a while, try disconnecting the gage
> line at the block. On my engine, the oil has drained out of the oil
> gallery & also some out of the copper line & out of the flex line. When
> the engine is started, some of the air is trapped in the line. If you
> ever have a "buzzy" oil pressure gage, loosen both ends of the line &
> let some air into it. Engine shut off of course.
>
> I can't imagine why bleeding the line would give more accurate gage
> readings. Whether you bleed the line or not has no effect on actual oil
> pressure. Pressure is pressure, be it air or oil. The fast oil pressure
> pulses are damped because air is compressible. Think accumulator.
>
> Can't say if the loop traps more air or oil. It certainly could help
> prevent vibration, but that's what the engine to oil pipe flex line is
> for.
>
> Regards,
> Dave Russell
> BN2
>
> Chris Masucci wrote:
> > I'm with you Dallas. From what I know of fluid dynamics, you're
> > right. The loops can provide no damping of pulses, since they are
> > full of fluid. I seem to remember a while back (on another topic)
> > other folks saying that you have to bleed the line at the gauge to
> > get accurate readings, or in other words, make sure there is no air
> > in the line.
> >
> > The loops can only be there to allow movement, so the lines do not
> > fatigue too quickly.
> >
> > Cheers, Chris BJ8
|