Are these vents and should you be able to blow air through them?

[Bigmuddyriver]

Was doing some maintenance on my bush hog decided to see if these were clear. I have two gearboxes on this machine. I removed them and couldn’t blow through them. Shouldn’t they be open to keep pressure from building up in the gearbox and blowing out the seals. Reason I ask I just recently had to replace a seal in the other gearbox.

 

[Rustyiron]

They are vents but usually not exactly "free air". The gearbox and oil slowly heat and cool and it doesn't surprise me that you can't blow through them with your mouth.
Think of it more as a filter.

 

[MossRoad]

Don’t they call those breathers?

 

[MossRoad]

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