2″ Vacuum Vent, Heavy Duty. Available in two (2) versions. Model #-050 is set to operate at pressures between 3.5 and 5.5 PSIG. Model #-100 is set to operate between 10 and 12.5 PSIG. Vacuum releases at .5 PSI on both models (for gravity flow only). Our standard spring is wound from 316 Stainless Steel. We also offer Teflon coated 316 Stainless as well as Hastelloy C which is one of the most universally corrosion-resistant alloy available. The Double Vacuum “RELIEVER” is made to answer the need of IBC users and others who require a breaker for gravity drain or pump out up to 50 GPM without the necessity of removing the fill cover.