Turbo Blow valves?

[Hotcrusader76]

Could someone please explain to me the reason for a turbo blow down valve for a turbo charged motor? Theory of operation and the sole reason it is there or was added to the car or truck?
I am leaning towards the reasons being:
It saves the turbo...but how and why?

[BrendellaJet]

is this the same as a waste gate?

[Hotcrusader76]

BrendellaJet:
is this the same as a waste gate?That's what I thought....but no its not..?????....I think 78Eliminator can comment on this, since he has the expierence in it...
He has a turbo civic he built.....I guess I'll wait for his response, unless someone else can clue me in...

[Jordy]

Are you talking about a pop-off valve? If so, that is to relieve excess boost spikes before you start blowing parts of your motor apart. They react a little quicker than a wastegate. Also, the wastegate is more of a bottom end tool to cut down on the turbo lag.

[HeavyHitter]

It all has to do with slamming the throttle shut. Ever hear a really hopped up turbo engine? Rally cars, GTP's, LMP's, all have that chirping noise as they go into corners. That's the turbo going to surge. Surge is when the compressor wheel can support the pressure any more and the air flow backwards over the blades. The easiest way to get this to happen is drive at WOT and full boost. Turbo is putting out a lot of air. Slam the throttle shut and the pressure goes sky high until it can't hold it in any longer(big shirping noise follows). It all happens at sonic speed so the impact on the turbo can shorten life dramatically. Big popoffs are now popular in the import drag racing scene. Turn the line lock on and rev the engine till the turbo is spooled up. Instead of sitting there at surge you blow off the excess air until you snap the throttle open. Viola, full boost just like a blower.