"Breather" plugs are normally designed to have minimal flow and simply allow the relevant annulus space to "breathe" and have no pressure difference due to temperature or changes in atmospheric pressure or very small fugitive emmissions.
you seem to be talking about something else "to allow air to escape in a high pressure cylinder?" but it is all very unclear. These are usually called vents.
Please provide more information (volumes, pressure, flows, diagram, picture etc) and a bit more explanation as to your question. I'm sure it's very clear in your mind and vision, but it's not in mine at the moment....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.