Pressure Vacuum Vent for Underground and Low Volume Tanks

FIG 749, 749BSP

Pressure vacuum vents are installed on the top of underground and low volume aboveground storage tank vent pipes. Vent allows tank to "breathe" during filling and discharging operations. Pressure and vacuum poppet seal vapors in tank when pressure is equalized. Settings are approximate. The 749T provides the same functions as the 749 and is designed for use on underground and low volume aboveground tanks storing Diesel Exhaust Fluid (DEF) and other products requiring PTFE and stainless construction. 


WARNING: Fig. 749 P/V vent must only be used in conjunction with motor fueling and/or low capacity flow. Fluid handling in lines larger than that used for retail service stations can cause tank to rupture or implode.

Standard Features

Screen protects the tank from debris and insects

 Integrated internal drain hole sheds water out and away from entering the tank

 Vents vapors out and upward per NFPA 30

 Conserves fuel

 Certified CFH ratings


Construction Details

  • 749
  • Body: Aluminum
  • Pressure poppet: Aluminum
  • Adaptor: Aluminum
  • Vacuum poppet: Brass
  • Pipe seal: Buna-N
  • Screen: 40 mesh stainless steel




  • Hood body: PTFE coated aluminum
  • Body: HDPE
  • Pressure poppet: HDPE
  • Vacuum poppet: Stainless steel
  • Pipe seal: PTFE
  • Screen: 40 mesh stainless steel



Certifications & Listings

CARB 95-14 (749CRB0500 model) or 95-15 (749CRB0600 model)

CARB 96-20 (749CRBS0500 model) or 96-19 (749CRBS0600 model)



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. Normal vents such as pressure vacuum and updraft vents for aboveground storage tanks should be sized according to NFPA 30 (2008) 21.4.3

Fig Suffix Size Description Weight
749 0100 AV 2" 8oz/ Pressure Vacuum Vent, Threaded 1
749 0200 AV 2"12oz/ Pressure Vacuum Vent, Threaded 1
749 1100 AV 3" 8oz/ Pressure Vacuum Vent, Threaded (2" w/3" Reducer Installed) 1.55
749 1200 AV 3" 12oz/ Pressure Vacuum Vent, Threaded (2" w/3" Reducer Installed) 1.55
749T 0200 AV 2" 8oz/ Pressure Vacuum Vent, Slip On, PTFE 1
749BSP 0100 AV 2" 8oz/ Pressure Vacuum Vent - BSP Threads 1
749BSP 0200 AV 2"12oz/ Pressure Vacuum Vent - BSP Threads 1


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CARB Certification

Morrison Bros. Co. has received approval from California’s Air Resource Board for a Phase 1 Enhanced Vapor Recovery System for Protected Aboveground Storage Tanks. Click here to get started on your CARB certification!

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