atmospheric and low pressure tanks, as well as providing a convenient access for tank cleaning, inspection and repair. Emergency relief valves provide relief from excessive internal pressure which may be caused by an abnormal condition, such as ruptured internal heating coils or an external fire. The Model 3900 does not provide vacuum relief and therefore vacuum relief must be supplied by the normal operating vent. For vacuum relief see Valve Concepts Models 3100, 3200, 3300 and 3600 series vents.
The manhole/emergency vent cover pallet provides an effective vapor-tight seal when the tank is not under emergency conditions. If the tank outbreathing requirements exceeds the capability of the normal pressure relief vent, under emergency conditions, the pallet will raise to allow vapors to escape, preventing damage to the tank due to excess pressure. The manhole/emergency vent weather hood is hinged so that when the excess pressure is relieved the pallet will reseat to again provide a vapor-tight seal or can be fully opened manually for acess to the tank.
OBJECTIVE The Model 3900 manhole and emergency pressure vents provide emergency pressure relief beyond that furnished by the normal pressure vent for...