Emergency relief vents provide relief from excessive internal pressure which may be caused by an abnormal condition; such as ruptured internal heating coils, an external fire, a failure of the tank blanketing system, a sudden cooling of the tank or a break in the tank wall.
The pressure pallet assembly provides an effective vapor-tight seal when the tank is not under emergency conditions. If the tank out breathing requirements exceeds the capability of the normal pressure relief vent,under emergency conditions, the pallet assembly lifts off the seat to allow escape of vapors, preventing damage to the tank due to excess pressure. When the excess pressure is relieved the pallet assembly will reseat to again provide a vapor-tight seal.
The 8900 Series manway pressure and pressure /vacuum relief vents provide emergency pressure relief beyond that furnished by the normal pressure vent for atmospheric and low pressure tanks, as well as a convenient access for tank cleaning, inspection and repair.