Thought I would mention something related to ProVent behavior after starting and taking for a spin my newly EGR/DPF/SCR deleted X5D.

Before deleting, I was running ProVent since January 2017. It looked to be doing its job separating oil from blowby - the return hose was always clear and free of oil.

In January-February of this year, I did a big project:
1. Replaced both turbos, suspected as culprit of severe oil leaks.
2. Deleted and tuned out: EGR, DPF, SCR.
3. Added a "normal" diesel cat (DOC).
4. Cleaned intercooler, pipes, intake.

At the same time, modified my ProVent setup, as I feel it was not quite what was recommended in this thread.
1. Replaced my hoses that while oil resistant, were softer than shoud have been with these (sgrice post)
2. Made the 3 holes larger, to match size (on photos) as ZetaTre's recommendation. My 3 holes were a little smaller.

So, after taking the x5d for a spirited drive, observed fumes coming out off the top of ProVent relief valve while idling.
Removed filter element and with mirror, confirmed the side valve is stuck closed. So, due to higher sucking powers of the new turbo and tune, that valve got stuck closed - exactly what ZetaTre predicted happens when he tested!

On the other hand, I observed the spring of the valve is not able to retract it quick and all the way.

So, decided to not drill more holes and instead stretch the spring.
After stretching, the valve retracted much more readily and farther.

Put it all together, did more testing and haven't observed fumes coming out of top relief valve.

Question: what is the function of that side valve anyway? It seems that it does nothing good in our case.

The rubber boot around the valve introduces a lot of friction, making the spring work harder. By design?