Pressure relief system for chemical storage tanks

A system for regulating pressure in a sealed chemical storage tank, the system comprising:

• a vent passage connected to the tank, through which gas may pass into and out of the tank, where the vent passage includes
• a seal pot having a top and a bottom,
• a first pipe portion extending generally downward from the tank to the top of the seal pot,
• a second pipe portion extending from the bottom of the seal pot to a low point below the bottom of the seal pot, and then extending upward to a level higher than the bottom of the seal pot, and
• a third pipe portion extending substantially horizontally from the second pipe portion at a level higher than the bottom of the seal pot,
• where the seal pot and the third pipe portion each define a volume;
• and
• a volume of liquid associated with the vent passage to constrain the passage of gas through the vent passage, where the volume of liquid is less than the volume of the seal pot and less than the volume of the third pipe portion;
• where increased pressure in the tank moves the liquid into the substantially horizontal third pipe portion to allow gas to pass through the third pipe portion;
• and
• where at least partial vacuum in the tank moves the liquid into the seal pot to allow gas to pass through the seal pot.