At what pressure should the BOV creep open?

[Thecrispynoodle]

The small bore pipe definitely keeps the valve closed.

The pipe opposite the small bore one should go to the MAF hose (the other way round to a BOV)

Correct, it's not excessive boost that pushed the bpv open it's the vacuum on the other side of the now closed throttle plate that pulls it open. A vacuum leak or tear in the bpv will hence compromise this.

[newsh]

The small bore pipe definitely keeps the valve closed.

The pipe opposite the small bore one should go to the MAF hose (the other way round to a BOV)

[UrS4boy]

stock BPV is "pull" type based on vacuum not "Push" type based on preload internal spring.if you installed wih wrong orientation,it became push type.

But there is still a spring that keeps the BPV diaphragm closed until a certain vacuum is reached.

[popdemonic]

stock BPV is "pull" type based on vacuum not "Push" type based on preload internal spring.if you installed wih wrong orientation,it became push type.

[UrS4boy]

S2 3B and ABY and RS2 ADU Boost Leak Testing

To test the valve: Detach the boost hose on the side of the valve and plug that hose up. Then pressure test as you would when searching for leaks.

S2 3B and ABY and RS2 ADU Boost Leak Testing:

http://www.s2forum.com/forum/showthread.php?t=63974&highlight=ABY+boost+leak

[VagOrBust]

Alternatively block the little vacuum pipe which will test your bypass valve diaphragm too as this should keep it closed.

I'm not sure if I understand this correctly: The valve receives boost pressure from the inlet manifold through the little vacuum pipe while under boost which significantly helps it to stay closed. So if you block the vacuum pipe the valve might open under boost pressure and this is not a failure.
To test the valve: Detach the boost hose on the side of the valve and plug that hose up. Then pressure test as you would when searching for leaks.

[DJones]

I get fluttering but when I reach 1.4bar boost, and not when but before lifting of the gas en quickly reengaging, not sure if that fluttering coming from wastegate ....

That sounds more like surge.

As said they will partially open on tick over as the inlet manifold is in vacuum. Atmospheric pressure or above (touching the throttle) should close it.

I use a Bailey and to set it I started off with a spring that I knew was to strong, I slowly reduced the preload until I didn't feel the transition (a shunting feeling) on lifting off the throttle and the Jobs a good'n...

Again as said just remove and block the pipe for boost leak testing. Alternatively block the little vacuum pipe which will test your bypass valve diaphragm too as this should keep it closed.

Cheers

Darren.

[sailaz]

I get fluttering but when I reach 1.4bar boost, and not when but before lifting of the gas en quickly reengaging, not sure if that fluttering coming from wastegate ....

[UrS4boy]

Simple question: BOV has to be closed or can be open while running on free rpm ? As soon as I push gas pedal a little bit it closes immediately. Is here everything ok ?

Should be closed on boost (or low vacuum) and open on vacuum based on the intake manifold pressure via the small diameter hose from the intake manifold to the small nipple on the end of the BPV. The spring inside controls the threshold vacuum point.

[VagOrBust]

Seems ok afaik. Open at idle and closing when pressing the gas pedal.
If it closes to fast you might get a little turbo fluttering when lifting of the gas en quickly reengaging at light boost.

[sailaz]

Simple question: BOV has to be closed or can be open while running on free rpm ? As soon as I push gas pedal a little bit it closes immediately. Is here everything ok ?

[VagOrBust]

Whilst boost leak testing my S2 (from the turbo to intercooler hose) I noticed the dump valve started to open and flow air at about 0.8 bar. Is this correct? same result was found with OE, Forge and forge copy BOV.

This may not happen when driving as the small bore pipe will be seeing boost and helping keep the BOV closed?

Thanks, Dan.

Hello Dan,

I've noticed the same behaviour on my new Kayser bypass valve. (The dealer doesn't supply the Bosch type any more.) It tends to flutter around 0.8 bar while I drive, making an annoying fart-like sound.
Think of it like this: If I drive around 80 mph and I would not have a turbo, then I would see around 0.6 bar absolute pressure in the air inlet manifold. Because I run the original turbo with tuning, the turbo slowly starts to rise the pressure to 0.8 bar and it start making this real annoying noise. (And off course, with the bypass still open before that it isn't doing any good).
My 2 cents: I think it opens to easy and I wonder if there are models of bypass valve that have a bandwidth between opening and closing. For instance: Opening at 0.6 bar, staying open until a minimum of 0.8 bar, so that the fluttering is eliminated.

[Rusty]

Don't block the intercooler hose, block the breather pipe hole in the inlet hose and do the whole system. Where are you blocking off at the turbo?

[Sleeper_Avant]

it will only stay closed dependant what spring pressure it is rated to internaly.

and yes the pressure/vacuum at the small pipe will keep it shut or vacuum depending when on or off boost.

just blank it off for your testing, extinguish the threat of that part being faulty.

alternativly i always use a smoke machine, never failed to find a leak yet

[UrS4boy]

Whilst boost leak testing my S2 (from the turbo to intercooler hose) I noticed the dump valve started to open and flow air at about 0.8 bar. Is this correct? same result was found with OE, Forge and forge copy BOV.

You should be running a By-Pass Valve (BPV or overrun cut-off valve in VAG-speak) NOT a Blow-off Valve. That said, a good BPV with no diaphragm leaks should remain shut except under engine vacuum:

http://forums.quattroworld.com/s4s6/msgs/20994.phtml