101 PSI (7 bar)
Double acting automatic poppet valve
They are heavy steel pressure vessels that are able to resist seven times atmospheric pressure.
They allow low pressure air to move in either direction through them, but they automatically shut when high pressure or “negative” pressure (less than atmospheric) is present in the ventilation pipe.
They also feature a manual lock shut capability in case you have malicious people outside your shelter attempting to dump water or fuel down your vent pipe.
As a high pressure wave from a nearby detonation passes over the shelter, the pressure travels down the pipes and into the shelter. If it is not stopped, it will destroy the air filtration equipment and injure or kill the occupants.
Directly behind this high pressure wave is negative pressure (less than atmospheric) because the atmosphere is blown outward from the center of the detonation leaving a partial vacuum. This phase of the detonation can be as dangerous as the pressure wave. If you’ve seen footage of a nuclear bomb test that has trees, you’ve seen the trees blown one way, then the other. The first direction is away from the blast as the blast pressure hits the trees, the second is the partial vacuum phase where the atmosphere is sucked back toward the center of the detonation. Watch the dust at ground level move in two directions in this video.
A blast valve with an air intake hose from the Safe Cell attached and the manual locking bar tethered by its retention chain.
A blast valve with an overpressure valve mounted on it. The locking plate is not visible in this image.
These blast valves automatically and near instantly close when the initial positive pressure wave from an explosion hits and automatically closes a second time (in the other direction) when the outside air pressure goes negative in relationship to the internal shelter pressure. When the outside air pressure returns to normal, the blast valve automatically returns to its normally open state. This allows to air flow into your Safe Cell and out of your exhaust port for normal operation, but will not allow a blast of high-pressure air to enter your shelter – and bring contaminants with it.
In an actual blast, the impulse of the pressure wave is much shorter than one second. Most valve manufacturers rate their valves using “incident” and “reflected” pressure ratings with the reflected pressure rating running about three times the incident rating. These terms refer to the characteristics of a detonation with incident being the direct blast wave and reflected being the direct blast wave plus a reflected wave from the ground or other flat surface that create aMach Stem of extremely high pressures for a very short period of time. The testing certificate that we have on these blast valves is for static pressure. Static pressure tests will return a lower pressure rating than a dynamic test because you take the variable of time out of the test. In other words, if a blast valve will hold 101 PSI for two hours, it will hold much more for 20 milliseconds. 101 PSI is seven times the atmospheric pressure at sea level. These valves are strong.
What’s included with this item
Two blast valves
Two heavy duty 1/4″ gaskets
Sixteen concrete wedge anchors (engineered fasteners able to hold the 101 PSI load rating when properly installed)
One masonry drill bit sized for the anchors
One hard copy of the installation and operation manual.