Internal underanding of N75 and vacuum resevoir please

[brasiliangringo]

As per attached pic, I have learnt how the variable vanes on my 52 reg 1.9tdi are ''angled'' by de-energizing the N75, causing pressure to flow through onto the actuator rod which angles the turbo vanes to generate boost, but I cannot understand how a vacuum is created to ''suck'' or pull the actuator rod back to reduce boost when the N75 is energized ?? I would also appreciate an image detailing the cross sectional view of a vacuum reservoir as cannot find on the www.. / or simply an explanation as to how it works?

Thanks in advance

UPDATE : I just learnt.. ''Vacuum pump is part of the tandem pump on the transmission end of your camshaft. The actuator pot has a strong spring inside of it that returns the actuator when vacuum is released.''