Protectoseal Series No. 51700 Hinged Emergency Pressure Manhole Cover Vents provide emergency pressure relief for storage tanks that are exposed to an external fire. They are designed to open and provide pressure relief beyond the capacity of the normal breather vents. The Series No. 51700 design allows for higher pressure relief settings than are available on our Series No. 53300 Manhole & Emergency Pressure Cover Vent. The Series No. 51700 Cover Vent does not provide vacuum relief. Vacuum relief must be supplied by an operating vent (See Protectoseal Series No. 830, Series No. 8540H, Series No. 6240, Series No. 16240 or Series No. 18540).These vents are mounted on the tank manhole flange. When properly installed, the device provides an effective vapor seal. Under emergency fire conditions, the cover can pivot open on its hinge and provide required relief, preventing damage to the tank due to excessive internal pressure. When tank pressure is reduced, the cover automatically recloses. The hinged design allows the use of a lever principal counterweight so that the pressure settings higher than those available on other dead weight loaded vents of similar size may be achieved. Full open flow capacity and automatic reclosing of vent as tank pressure decreases provide efficient and dependable emergency venting capability while minimizing amount of vapor unnecessarily vented to the atmosphere. The design also allows convenient access through the manhole opening for tank inspection and maintenance.
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