At 11:03 PM 7/17/2001 -0400, Kai M. Radicke wrote:
>>.... "air pump from large American V8" are not fan type blowers but are
vane pumps ....
>
>.... I suppose it would be the Detroit auto makers who would take the
cheapest and easiest route to producing an air pump.
The air pump became almost universally standard issue in the US in 1968 in
compliance with the first federal emissions standard (and maybe a little
earlier in California). Just about every auto manufacturer supplying the
US market took the same approach, including the British manufacturers,
which is why most air pumps look like kissing cousins. And yes, cheap is
(was) the driving force in that decision (as is normal in the economic world).
>However, that said a vane type pump would be even worse in a supercharger
application...
Careful. Worse than what? They have much better throttle response and low
end torque than an exhaust driven blower.
> do they still make Judsons, no. Do those V8 Airpumps have external
lubrication for the vanes? The vane types are typically high friction and
need the lubrication of the vanes to stop the wear of the vanes and to
create a good seal.
No, the air pumps don't have any external lubrication for the vanes. For
their original intended use they run quite low pressure, so generate only a
little heat, so they do quite well without. But they would likely get
fried quick at higher pressure and speed without some lubrication.
>That said, a Judson is still a pretty big vane type supercharger... and I
don't know if the displacement of an airpump would be comparable.
You're right. Not even close. Just look at the size of the output pipe on
an air pump, and you will know immediately that it wouldn't have the
capacity necessary to be used as a blower for combustion air intake without
grand overdriving. Well, maybe the largest V8 air pump could provide
moderate intake boost for the smallest car engines, but we be talking
something under one liter engine size.
>Remember a Judson is pretty much only effecitve for 5.5-6.5psi.
Yup. In theory all you need to generate higher pressure is a bigger
blower, but, higher pressure generates more heat, which is fighting the air
density curve, so it takes a proportionately larger compressor to get much
higher boost. Today's screw type compressors are much more efficient
superchargers and operate quite well at higher pressure. More reason on
why below.
>And no I never looked inside of an air injection pump either, it just
comes as a surprise to me that a straight vane design was used...
Why surprise? Inside there is a one piece hub with radial slots and
several flat rectangular vanes, running off center in a cylindrical
housing. Super simple, really cheap, and it serves the purpose.
>> The main problem(s) with a vane type compressor is heat and noise, both
of which lead to compressor inefficiencies.
>
>Right. Heat from the friction of the vanes touching the body of the pump,
and heat from the compression process.
The friction is not much. Most of the heat is from adiabadic compression
of the air. You can look up that formula in almost any engineering
handbook. The noise comes from the sudden opening of the pump intake port
with a partial vacuum already inside, and the sudden opening of the pump
outlet port with high pressure inside, both of which result in very sudden
changes in air velocity. This makes a clap like thunder on both sides, and
the resulting turbulence generates even more heat and really messes with
the pumping efficiency.
>This is actually a current conversation on the Judson list...
Not sure we what them to know we're talking about it over here. They might
come preaching the virtues. >8O
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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