This hand operated bellows slip-fits instantly into the top of the Safe Cell and is operated by pumping it up and down. It is used to draw filtered air into a protected space during a long term power outage.
A typical shelter occupant cannot physically maintain an overpressure with this device (truth in advertising), but you can draw in air through the filter bank and into your shelter, displacing the carbon dioxide that is exhaled by the occupants ~and~ you still have safe, breathable air being filtered for NBC toxins.
The constraint for maintaining an overpressure in any decent sized shelter (larger than a coat closet) is human endurance - there is simply too much air to move, either by a plunger system (which we have), or a rotary crank system, to maintain an overpressure for more than a few minutes. Either way, the oxygen that you consume and the carbon dioxide that you exhale while you bring in filtered air by hand power is beyond what humans can accomplish.
Our emergency backup bellows has an output of 50 cubic meters (1766 cubic feet) per hour at 50 strokes per minute using a 7 inch stroke and an output of 100 cubic meters (3200 cubic feet) per hour at 50 strokes per minute using a 14 inch stroke.