Turbo engine Blow Off Valve location, advantages and detriments? 1

[MRDAGERUS]

Gentlemen,

When I look at the pictures of BOV installations for small turbo engines, some questions came to my mind.
Is the BOV placement in an immediate proximity of the compressor outlet a bit counterproductive?
When the BOV valve opens, it creates a reverse flow of the large volume of air from the plenum and the chargecooler towards the turbo.
When the pressure in the duct drops and valve closes, a shock wave hits the compressor inducer in reverse direction creating a surge (which we are trying to mitigate by installing the BOV!).
BOV location between the plenum and the chargecooler seems to be a better solution; however it may have similar adverse effect.
BOV location at the plenum (or close to it) may be the best, because it will not create a reverse surge in the pipe connecting the plenum to compressor outlet.

Your thoughts?

 

[MRDAGERUS]

Here is the picture of an "intermediate" BOV location

 

[MRDAGERUS]

And, hopefully, the best (?) location.

 

[BrianPetersen]

Arrange the valve so that it does not open and close as abruptly, and your (probably imaginary) theoretical non-issue goes away, no matter where you put it.

 

[dgallup]

Second & third links don't work for me.

I don't think there is any back flow from the CAC, just a reduction in the airflow rate into the cooler.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Lou Scannon]

The valve is emptying the volume between the compressor and the throttle valve. It seems to work a little better when the valve is close to the throttle valve, since the flow direction for most of the volume does not have to change, as indicated by the OP. It is also kinder to the blow-off or recirculation valve (not to mention the compressor, in the case of a recirculation valve), to locate it after the charge cooler. It is possible to have extended periods of recirculation, if the valve is manifold vacuum operated, when the vehicle is cruising at moderate to high part load, e.g. climbing a grade, or towing. The valve should be selected, and located in the air system, with this in mind.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[MRDAGERUS]

Thank you Hemi!
You are right, closer to TB-s is better.

Brian,
Could you elaborate on your notion of "non issue" and "arrange" in non-presumptuous way?

 

[BrianPetersen]

If the blow-off valve is properly sized, it should release only enough flow to keep the compressor out of surge as it spins down. It does not need to do so violently. There is no need for it to do it so quickly and violently as to create a "shock wave".

Even if it does open violently ... there is no need for it to close violently. I can understand wanting to open it quickly to keep the compressor out of surge, but it need not close so quickly. Even if it takes (say) a quarter of a second to close, that's not fast enough to create a "shock wave". The only way the driver would notice is if they got back on the throttle during the closing period ... but if the valve is sized to release only enough flow to keep the compressor out of surge (as opposed to being grossly oversized), the turbo will easily overwhelm that slight temporary "boost leak" if it is actually operating under load.

And even if all that is disregarded ... The real thing that the turbo won't like is a surge condition (approaching dead-heading) under load (while it still has significant pressure ratio across it). The blow-off valve itself is responsive to the pressure in the intake duct at the location where it is installed. If there were to be something approaching a "shock wave" caused by the backflowing air, the blow-off valve itself would see the increased pressure at that location and simply open again (or stop its closing motion, as the only foreseeable condition in which this might happen is while the valve is in the process of closing).

I have never heard of the issue proposed by the original poster being a real-world cause of turbo failures.