[s-cars] By-pass valves

Thu Aug 12 07:10:59 PDT 2010

Thanks Scott, Dave, et al;
I understand the Bosch Audi OEM's operation pretty well as described by Dave and Scott.
Having said that, my question was, and is, should the OEM plastic valves open on the bench with vacuum applied to the small control port? The Forge aluminum valve does, but neither of my OEM plastic units will, and I hear what seems to be air bleeding by the diaphragm when vacuum is applied.
They have never (at least in my ownership) been installed backwards, but wondering if they need to replaced and tossed, or if they are as normal for a stock OEM. I'm guessing from this behavior that the diaphragm is ruptured and they are toast?
TIA

Dennis 
Denver

-----Original Message-----
From: qshipq at aol.com
To: djdawson2 at aol.com; benswann at verizon.net; esanborn at gmail.com; dgraber460 at aol.com
Cc: s-car-list at audifans.com; quattro at audifans.com
Sent: Thu, Aug 12, 2010 7:36 am
Subject: Re: [s-cars] By-pass valves

Agree, many are mixing bypass valve operation with blow off valve.  I have not seen any bypass valve that boost helps 'blow open' from below.  Most (all audi apps) are oriented as DJD explains with the boost 90degrees to the diaphram.  The HKS sequensial bypass valve is oriented with the diaphram in line with the boost pressure.  However, it's operation is spring adjusted and operates as a stepped  'needle valve', so it's still the feed line on the device that dictates valve opening and close.  

A blow off valve oriented with the diaphram in line with boost pressure,  has no intake feed, it is an absolute boost pressure device that pops when the boost in the intake manifold exceeds a set pressure.  

Scott J

-----Original Message-----
From: djdawson2 at aol.com
To: benswann at verizon.net; esanborn at gmail.com; dgraber460 at aol.com
Cc: s-car-list at audifans.com; quattro at audifans.com
Sent: Wed, Aug 11, 2010 11:20 pm
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>

Subject: Re: By-pass valves

To: dgraber460 at aol.com

Cc: s-car-list at audifans.com, quattro at audifans.com

Message-ID:

    <AANLkTin-vkgjJaotOtbbX3ToE1Ab-yLvLzkJ2293n-xq at mail.gmail.com>

Content-Type: text/plain; charset=ISO-8859-1

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

]

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