It can be adjusted to increase the positive pressure inside your protected space. The positive air pressure is what resists airborne toxins from migrating into your protected space through cracks or holes in the shelter.
It can be attached directly to the inside wall or ceiling or on a blast valve.
The adjustment cap is located at the bottom of the valve assembly. Tightening this cap increases the pressure in the protected space. This allows you to compensate for a shelter that is not entirely sealed up – within reason. This valve should be used with the differential pressure gauge. so you can see the difference in pressure as you adjust it.