Morrison Bros. 748A Pressure Vacuum Vent is designed for installation on top of the vent pipe of an aboveground or underground storage tank. The brass poppets seal vapors in the tank when pressure is equalized. The vent allows the tank to "breathe" during filling and dispensing operations.
This vent must be used in conjunction with an emergency vent. It is recommended that the opening pressure setting is set below that of the emergency vent so the normal vent operates first. Settings are approximate.
Note: Normal vents such as pressure vacuum and updraft vents for aboveground storage tanks should be sized according to NFPA 30 (2012) 21.4.3.
- Vents outward and upward in compliance with NFPA 30
- Tri-polar mounting screws for mounting exhaust hood in any of three positions
- Optional dryer connections accommodate the installation of desiccant dryers on vacuum connection
- Type: Pressure Vacuum Vent
- Series: 748A
- Size: 3 in. FNPT
- Pressure Setting: 6 oz./sq. in.
- Venting Capacity: 43,000 SCFH @ 2.5 PSI
- Vacuum Setting: 1 oz./sq. in.
- Poppet Material: Brass
- Seat Material: Passivated Aluminum
- Body/Hood Material: Aluminum
- Screens: Stainless Steel
- Dryer Connection: 3 in. FNPT
- Pressure Discharge Hood: No
- Height of Vent: 14.37 in.
- Width of Vent: 13.37 in.
- Weight: 12.15 lbs.
WARNING: DO NOT FILL OR UNLOAD FUEL FROM A STORAGE TANK UNLESS IT IS CERTAIN THAT THE TANK VENTS WILL OPERATE PROPERLY. Morrison tank vents are designed only for use on shop fabricated atmospheric tanks which have been built and tested in accordance with UL 142, NFPA 30 & 30A, and API 650 and in accordance with all applicable local, state, and federal laws. In normal operation, dust and debris can accumulate in vent openings and block air passages. Certain atmospheric conditions such as a sudden drop in temperature, below freezing temperatures, and freezing rain can cause moisture to enter the vent and freeze which can restrict internal movement of vent mechanisms and block air passages. All storage tank vent air passages must be completely free of restriction and all vent mechanisms must have free movement in order to insure proper operation. Any restriction of airflow can cause excessive pressure or vacuum to build up in the storage tank, which can result in structural damage to the tank, fuel spillage, property damage, fire, injury, and death. Monthly inspection, and immediate inspection during freezing conditions, by someone familiar with the proper operation of storage tank vents, is required to insure venting devices are functioning properly before filling or unloading a tank.
748 Series Pressure/Vacuum Vent Product Manual (PDF Download)