I've always wondered on blow off valves whats that little nipple that connects to the vacuum line do? Does it tell when the piston to open and close? What would happen if the nipple was uncapped altogether. Will the valve always stay open or always stay closed?

 

Recirculating, just leave it alone.

 

That nipple/port is there to give a pressure/vacuum reference to the top of the valve.

Removing it will prevent the valve from operating properly and can create compressor surging that will eventually lead to damage to the turbo and potentially the engine as well.

Just leave it connected.

 

Don't cap it, it's there to help hold high pressure boost beyond spring capacity

The nipple allows the BOV to open a little under vacuum, and to close a little under boost. It works in conjunction with the spring inside which is spring loaded to closed. Under high boost the spring tension isn't enough to keep it fully closed so the nipple provides a boost source to enter the chamber on the spring side
and works in conjunction with the spring to keep it closed.

On a typical setup, capping the nipple will make the valve vent much of your built boost and would be like a huge recirculating boost leak.

 

Thanks for the replies. I wasn't actually planning on leaving the nipple unhosed. I was just doing research on how blow off valves work and its hard getting detailed info on google about this topic.

 

^ Try Howstuffworks.com for some more info.

 

The nipple on the BOV is what is used to control the opening and closing of the BOV. A high enough vacuum opens it (when vacuum overtakes the spring pressure), and pressure keeps it closed.

If you leave the hose off, the BOV will stay closed. It will eventually open once the boost underneath the valve seat reaches a high enough value, but that will be a very high number sine the area under the seat is much smaller than the area inside the valve that the vacuum is acting upon. Also, leaving the hose off will not allow the air to blow off between shift, or very poorly, at best, leading to failed bearings in the turbo.

Some of these replies didn't explain it that well, but that nipple is what controls the BOV...definitely keep it connected.

Eric

 

I intentionally left my reply brief.

Regardless of HOW it works, it needs to be kept connected.

 

Read this and you will understand ok maybe overstand all about bov's.

https://www.evolutionm.net/forums/sh...ad.php?t=24611