9E ventilation

Hello everyone
We have GE frame 9E gas turbine and it has 88BT, 88JS, 88VL and 88VG (two for each)
All of them are drawing air for their compartments except for 88VG it pressurize the air inside the load compartment.
Can someone explain to me why is this ?
(Why 88BT drawing air while 88VG is pushing it. Is there any advantage in each one?)
Or lead me to a reference, article or anything that explains to me.
Thank you in advance

Actually, the in/out directions of compartment ventilation air have changed multiple times over the time GE has been designing heavy duty gas turbines--for many reasons.

The Load Compartment is a hot place to begin with, and so it is felt it is best to pressurize it with outside air than to try to draw outside air into the compartment for cooling. I believe the CFD (Computational Flow Dynamics) studies show that there is more cooling by pressurizing the Load Compartment with outside air than by trying to draw into the compartment to cool it--better air circulation and a higher exchange rate, which translates to more cooling.

Since the Load Compartment isn't very large the opening(s) for being able to draw air into the Load Compartment couldn't be very large either, so pressurizing the compartment allows more air to flow into (and through) the compartment.

Finally, because the air used to cool the Load Compartment gets pretty hot absorbing heat as it passes through the load compartment a fan used to draw into and through the Load Compartment would get very hot, also. This has cause rubs (and sparks!) and failed bearings. So, moving cool outside air with the fan into the Load Compartment also keeps the fan itself cooler and prolongs safer operation.

Hope this helps!