Our line of 556 valves, which are available in various pressure and cover configurations, are used extensively in the military shelter industry. The valves serve multiple functions. First they provide pressure relief for the otherwise destructive differential pressures that develop during air transport. Once on the ground, differential pressures occur due to changes in ambient temperature, barometric pressure, and when doors are opened and closed. Pressure-relief valves help protect seals, sensitive electronic instruments, and the shelter structure from damage.