[s-cars] While we are on the subject of WGFVs...

[Djdawson2 at aol.com]

In a message dated 1/11/2006 7:10:43 PM Mountain Standard Time,  
tmullane at gmail.com writes:

I can't  explain the mysteries of the universe, but I do know that the
basic WGFV  functions as Teddy and I described it.  When power is
applied, all  ports are joined.  All you need is a WGFV, a battery, and
breath of  air to test and confirm this.
 
Tom,
I am well aware that what you and Teddy have stated is true.  I have  never 
debated that fact.
 
 

Remember  that the spring only needs to hold the WG shut against
exhaust gas pressure  inside the exhaust manifold.
 
 
I am also well aware of this fact.  I would guess that I've been to as  many 
turbo system design seminars as anyone on this list... as fleet management,  
design, and specification (mostly diesel and natural gas turbo vehicles) is 75% 
 of what I do for a living.  I'm not trying to be conceited, but I do know  
what I'm talking about when it comes to turbocharging systems.
 
 
 

The only  boost to affect the spring comes from the WGFV when it is  closed.
 
 
Agreed.
 
 

Exhaust  manifold pressure is related to the exhaust system flow, not  boost.
 
 
Agreed... partially.  As boost builds, so does exhaust manifold  pressure... 
and the only relevant pressure to our discussion is that found  between the 
cylinder head, and the turbine wheel.
 
 


Think about what happens when you disconnect the WGFV from the WG  -
boost goes sky high.
 
 
No... it will only build to about 14-15psi.  That is why it is called  a "1 
bar" spring.  The spring is designed to provide just enough "push" to  hold the 
WG shut to 14.7psi... no more, no less.  AND, it only performs to  this spec 
if it is used in the original configuration... meaning EM and  turbo.  Throw a 
header and a different turbo into the mix, and the  pressures change... and 
so will the boost level allowed by the spring.
 
 

In this case, the only thing that can overcame the spring and open the WG is  
pressure of the exhaust inside the manifold.




Yep.  But knowing that the spring is only good for 14.7psi of boost  
(unassisted), how would you explain being able to run double that?  The  only 
explanation is vacuum to the bottom of the diaphragm of the WG.  I did  a little 
search on the web, and the best drawing I could find without turning  this into a 
big project, was this:
 
_http://www.2linc.com/venturi_vacuum.htm_ 
(http://www.2linc.com/venturi_vacuum.htm) 
 
As you can see in the diagram, if all 3 ports are open (which they are in  
the WGFV when power is applied) you have created a venturi vacuum generator,  
with pressure entering the side of the fixture, just like our WGFV.  This  
creates the vacuum that holds our WGs shut.
 
You can prove all of this to yourself with one simple test.  Clamp or  
disconnect the line to your WG and see what boost you can achieve.  It will  only be 
about 15psi.
 
If you want to take it a step further, connect a vacuum gauge to the line  
between the WGFV and the WG.  You WILL see vacuum there, and it is what  helps 
the spring keep the WG shut at boost levels above 15psi.
 
I hope this email doesn't sound blunt... it wasn't intended to... I do  enjoy 
the discussions, and consider them friendly.  I hope you do  too.
HTH,
Dave