Drums of flammable liquids require venting to relieve pressure build-up due to heat and also to prevent creation of a vacuum when liquid is being drained off or the drum is subjected to sudden cooling. In event of fire, the hazards of drum leakage or explosion due to excessive pressure build-up can be catastrophic. Either pressure or vacuum can cause failure of the container. What's the best way to solve this issue? The solution is obviously to buy the Justrite Safety Drum Vents! Justrite Drum Vents provide automatic pressure relief. Operating valve opens at five psig internal pressure in normal service. Vacuum relief is manual or automatic depending on the model and permits four or more gpm flow through a standard .75" faucet. All vents include a flame arrester for added safety.Do you order this product often and/or in large quantities? Check out our Large Order Program to save yourself time and money.