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Re: [T3] what is this piece? (FI)


On 11 Feb 2004 at 22:59, David V.N. wrote:

> From: "Jim Adney" <jadney@vwtype3.org>
>  >
> > I've taken them apart and they are just an empty box. I don't see how this
> > could possibly have any effect at all; the hose, being rubber and
> flexible,
> > should have a greater damping effect, plus this kind of pump really
> doesn't
> > have pulsations.

> I noticed that the connections are offset.I would imagine that any pulses
> that were present
> wouldn't be passed directly down the line.I've seen similar "tanks" in line
> with Wilden pumps
> that DO produce prodigious pulses.

Yes, I wonder about the offset, too, but hydraulic pressure and pulses really 
don't care about corners, they should have no effect. There are only 2 ways 
that I can see that these "boxes" could have an effect. 

One is if the offset was in such a direction that an air bubble would always be 
trapped there. The air bubble would be compressible and this would make a 
"shock absorber" which would even out the pulsations. The problem I have with 
this is that I can't imagine that an air bubble would stay there.  

The other would be if there had been a small air-filled rubber balloon in 
there. This would serve the same function as the bubble, but could not be 
washed downstream. I've never seen any sign that there was such a thing in 
there.

I also don't think I've seen this "damper" on any of the other D-jetronic cars 
I've worked on over the years. Type 4s and 914s don't have it, and I don't 
think Volvo or M-B did either.

Later Bosch FI systems used an actual accumulator with a spring and a rolling 
diaphram. I've often thought of adding one of those to my system, but it never 
seemed worth the bother. The only advantage would be to completely eliminate 
the hot soak boiloff problem, for which there is already a fairly easy 
solution.

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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