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FIG 948A

Pressure Vacuum Vent

The 948A pressure vacuum vent is designed for installation on top of the vent pipe of an aboveground or underground storage tank. The poppets seal vapors in the tank when pressure is equalized. The vent allows the tank to breathe during filling and discharging operations.

NOTE: UL 2583 was released in 2011 and becomes effective December 30, 2013. This listing covers requirements for mechanical type accessories that are typically intended for attachment to fuel storage tanks or their connecting pipes in fueling system applications.

WARNING: DO NOT FILL OR UNLOAD FUEL FROM A STORAGE TANK UNLESS IT IS CERTAIN THAT THE TANK VENTS WILLOPERATE 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.

Product Features

Standard Features

Conserves vapors

Durable construction

Easily replaceable seals extend life expectancy

Outlasts other brands by many years of service

Operating temperature -40°F to 130°F

Full 2″ orifice for maximum flow rate

Compatible with gasoline, ethanol (to E-85), and biodiesel (to B-20)


Construction Details

  • Body: Anodized aluminum
  • Seals: Elastomer
  • Screens: Stainless steel
  • Handle: Stainless steel
  • Rainguard: Aluminum


Leak Rates and Settings

Pressure leak rate: Less than 0.05 SCFH @ 2.00″ WC

Vacuum leak rate: Less than 0.21 SCFH @ 4.00: WC

Opening pressure: 2.5″ to 6.0″ WC


Flow Rates

36,720 SCFH @ 2.5 PSI

23,400 SCFH @ 1.0 PSI


Certifications & Listings

UL 2583 listed; 948A Pressure Vacuum Vents meet the requirements of EPA 40 CFR part 63 for Gasoline Dispensing Facilities; Missouri Air Conservation Commission Approved for Rule 10 CSR 10.2.260 and 10.5.220

Product Ordering Instructions

Figure Suffix Size Description Weight (lbs)
948A 0200 AV 2” Pressure Vacuum Vent 2.5” - 6.0” WC Pressure 7.70