Harbor Freight blast cabinet question

[Threadkiller]

Morning all,
I recently acquired a harbor freight benchtop blast cabinet. Although I haven't use it yet, It seems like a decent unit but the instructions are horrible. There is a large air vent in the back and it came with a plug/cap. Now I've never used a blast cabinet before so go easy on me. Should this be capped when using? I assume there will be a positive pressure situation in the cabinet when I am using it, so it seems as this vent cap would blow out? Wont media get everywhere if its left open? There is a baffle in the way but still. Ive attached a picture from a screen shot on youtube of what I'm talking about.

 

[rlitman]

You should have a dust collection system pulling negative pressure on the cabinet, so the vent should allow fresh air in, to keep the cabinet from collapsing.

 

[BORING HOP YARD]

I would start here, lots of good information.
https://www.garagejournal.com/forum/threads/the-abrasive-blasting-resource-thread.237844/
I have the older version of the "red" blast cabinet that has the vacuum port on the side wall, the hole your showing allows air to be pulled in. Good information about modifications to improve the unit.

 

[Threadkiller]

Ok, that makes sense. Thank you for the replies! I will check out that link, thank you.