American Safe Room manufactures this 7 bar (101 PSI) double acting automatic blast valve. They mount on the ceiling or the wall directly over the intake and outflow ventilation pipes using the included concrete wedge anchors and a heavy duty gasket.
A blast valve is a heavy steel pressure vessel that allow the relatively low pressure air from the NBC air filter to move in either direction through them, but they automatically slam shut when a high pressure blast wave or the following negative pressure vacuum phase comes down the ventilation pipe. Our blast valve is engineered to resist seven times the normal atmospheric pressure.
This blast valve also feature a manual lock shut capability in case you have malicious people outside your shelter attempting to dump water, fuel, or smoke down your ventilation pipes.
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.
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.
American Safe Room certifies that the ASR-101-BV explosion resistant blast valves are tested to meet or exceed the following specifications:
Type – automatic double acting blast valve
Weight – 25.0 pounds/11.3 kilograms
Minimum closing pressure – 0.5 PSI/3.5 kilopascals
Maximum operating pressure – 102 PSI/703 kilopascals
Minimum operating temperature – minus 15 F/minus 26 C
Maximum operating temperature – 212 F/100 C
Static airflow resistance (pressure drop):
0.15 inch of water column at 100 CFM
0.25 inch of water column at 122 CFM
0.50 inch of water column at 148 CFM
0.75 inch of water column at 187 CFM
1.00 inch of water column at 218 CFM
Construction, body – A-36/1018 steel
Construction, valve heads – 304 stainless steel
Construction, seals – BUNA synthetic rubber
Construction, guide bushing – 60-60 Bronze
Mounting – 8 each 5/8”/16mm holes on 10.2”/260mm bolt circle
The blast valve manual has complete installation instructions.
This is the professional engineer’s stamped certification of a static pressure test of these valves. The valves held the pressure for two hours.
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 a Mach 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.
Alternate Installation for Steel Shelters
Also available are weld-on mounting flanges for the intake and outflow pipes. They are sized for 4 inch, schedule 40 steel pipe.
The vent pipe shown has the mounting flange welded onto it.
The gasket and the blast valve are held in alignment with a piece of allthread for this picture.
In this installation, the steel vent pipe penetrates at least two inches into the shelter. You cut a 4.5 inch hole in your shelter, stick the pipe through it and weld the pipe in place. Then this flange is welded onto the very end of the pipe.
We substitute bolts, nuts, and washers for the concrete wedge anchors and the blast valves are bolted onto these flanges. The gasket is sandwiched between the mounting flange of the blast valve and the the flange welded onto the pipe.
Price, availability, and ordering
Blast valves are sold individually, but usually installed in pairs – one on the intake pipe and one on the outflow pipe. Shown in this picture is everything that comes with two blast valves
Part number: ASR-101-BV
Price: $525 each, plus shipping
Availability: Stock item
Manual: Blast valve manual
One blast valve
One heavy duty 1/4″ gasket
Eight 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.
How to order: call 541-459-1806, Monday through Friday, 8:30 AM to 3:30 PM, Pacific time