[s-cars] By-pass valves

[Ben Swann]

Yeah, I did  realize after I sent that - should have reviewed that before sending.
Good you clarified.
 
I meant to say positive intake tract pressure (pre-throttle/post turbo) rather than
manifold pressure.   
It is the combination of Forced induction/boost (high intake tract pressure) + manifold
vacuum that occurs when throttle is closed abruptly, that triggers the valve to open and
divert pressure.
 
Anyway, the main point I was trying to make is that if the valve is installed backwards,
It will not open correctly - meaning it might not open at all, or open pre-maturely, or
flutter. 
 
Also, there are variations on the stock valve. Although it is not the most robust valve
out there, the #..# 710N valve has a metal diaphragm and does not fail like some of the
other OEM valves.  They look the same, but the 710N is a better unit. Even the 710N is
not very good for boost levels over 1.5 bar (2.5 absolute).
 
Ben

  _____  

From: djdawson2 at aol.com [mailto:djdawson2 at aol.com] 
Sent: Thursday, August 12, 2010 12:21 AM
To: benswann at verizon.net; esanborn at gmail.com; dgraber460 at aol.com
Cc: quattro at audifans.com; s-car-list at audifans.com
Subject: Re: [s-cars] By-pass valves


Mixing terms... and what you're saying isn't really accurate.

The valve, is normally closed.  Apply a vacuum and it opens.  Apply boost and it remains
closed.  The signal comes from the intake manifold.  The intake manifold in a naturally
aspirated engine is always in some state of vacuum.  This means that if you are not
making any boost, there will be a vacuum in the intake... inclining the BPV towards
opening.

Positive manifold pressure will NOT  "assist to force or blow the valve open when vacuum
is applied to the control port" because those 2 things can't ever happen at the same
time.  If there is pressure in the intake, there is pressure forcing the BPV to remain
closed.  When there is vacuum in the intake, there is vacuum at the BPV opening it up.
Furthermore, boost hits the *side* of the piston (Forge) or diaphragm (Bosch)... never
able to assist in opening the valve, unless you have it improperly installed.

If as stock BPV is installed backwards, you will blow the diaphragm in short order...
it's just rubber, and it won't last long fighting 20+ psi.

The BPV's purpose is to alleviate pressure stall in the intake plumbing (and therefore
the turbo) when the throttle closes.

Anyway....



-----Original Message-----
From: Ben Swann <benswann at verizon.net>
To: esanborn at gmail.com; dgraber460 at aol.com
Cc: 'Quattro List' <quattro at audifans.com>; s-car-list at audifans.com
Sent: Wed, Aug 11, 2010 6:51 pm
Subject: Re: [s-cars] By-pass valves


No, just the opposite.  The Bypass valve is normally closed.  The control port is vacuum
actuated and tends to open the valve.  Positive manifold pressure will assist to force
or blow the valve open when vacuum is applied to the control port.  This happens only
when the throttle valve snaps shut while engine is under positive pressure - 

like  between shifts.



So the mityvac test is not necessarily going to tell you if the valve is opening
properly and some valves have beefier springs for higher boost pressure.


Also, if the valve is installed backwards then it may not open or flutter when  opening,
or open when it should not open.  Funny thing is the way most valve are   oriented, the

correct way does not look correct.  You  might want to verify that the direction of the
valve is correct.


See: http://www.gtquattro.com/Bypass-Valve.html that has a picture of how the valve is
connected/oriented.



Ben


[Date: Wed, 11 Aug 2010 17:56:43 -0400


From: Eric Sanborn <esanborn at gmail.com>


 : 


I might be misunderstanding what you were testing, but they should only open   during
boost


On Aug 11, 2010 5:12 PM, <dgraber460 at aol.com> wrote:


List-et-al;


I have been chasing a full throttle issue on my 3B'd URQ for a few months  now. The
symptoms have been a flattening and lack of power under full  throttle. My boost gauge
has always shown full boost at 19-20, and it throws  no codes. I started to notice the
moaning (not whooshing) noise when off   throttle, which I had heard before and found to
be an aluminum bypass valve  that needed cleaning.




Since it had been running an OEM Bosch plastic valve, I pulled the Forge  valve off the
S-Car and cleaned it up and installed it. On the drive this AM  it seems to have cured
the issue. Time will tell if total cure.




The question I have is that I tried to test all 3 valves that I have while  messing
around last night. I have 2 plastic, and 1 Forge valve. I hooked up  a vacuum pump that
pulls 14 lb hg to each valve individually and _none_ of  them would pull open. Then I
used my little Mighty Vac hand pump and the  Forge valve would pull open and stay.
Neither plastic OEM valve would open  with either test. Does this indicate both OEMs are
toast?




I assume the vacuum pump did not have a check valve and therefore could not  "build"
vacuum as the Mighty Vac did, thus letting the valves flutter but  not pull open. Sound
reasoning?




Also - is there a recommended lubricant that keeps the aluminum valves  happy, and
functional, or should they remain dry?




Dennis  Denver ]