Slide Throttles

[Todd Knighton]

SRavet at bangate.compaq.com wrote:
> 
> Todd Knighton <knighton at net-quest.com> Wrote:
> |
> | SRavet at bangate.compaq.com wrote:
> |
> | > OK, what is a slide throttle?  I thought it was simply a "cover" that
> | > slides over a "hole".  But that wouldn't tend to stick closed.  so what
> is
> | > it?
> | >
> |
> |       It is just a plate over a hole, but try this.  Put a ruler on the
> | ground and move it around, easy right.  now have someone stand on it, a
> | little more difficult.  Same idea, because of the great pressure
> | differential caused by turbo motors and supercharged motors on surge,
> | the plates have an enormous amount of pressure placed on them.  They
> | tend to deflect and stick in the tracks because the tracks are precision
> | machined for a good seal and no rattle in the vertical direction.  Apply
> | a bit of curvature in a linear track, uhnt wallah, we have schticking.
> 
> Doesn't the wastegate vent that pressure?
> 

A wastegate vents the pressure from the exhaust system to decrease the
energy potential of the exhaust entering the turbine.  The turbocharger
however maintains quite a bit of momentum / intertia due to it's 130,000
rpm's and mass and does not slow instantaneously upon throttle closure. 
Thus, you get surge.  The throttle closes, the air flow continues from
the turbocharger to the point where the pressure overcomes the flow and
the flow then reverses through the compressor, being that it's not a
positive displacement blower like a roots type blower.  And depending on
the application, you'll see from 25 to 100 psi in the intake before flow
reversal occurs.  That's hard to deal with.  A blow off valve decreases
the problem, but loses pressure in the intake and creates turbo lag
between shifts.  Cure one problem, create another.

> Next, what is a barrel throttle?
> 

Some one earlier described it well.  Take a tube a lay it across your
port.  Put another tube inside it, but make this one solid.  Punch a
hole through 
both tubes.  Now when you rotate the inside tube you can open and close
the port.


Todd Knighton
Protomotive Engineering