GPI 906001-4, Pressure Vent Cap with 2-Inch NPT Cast Iron Base for Vented Fuel Storage Tank, 3 PSIG Pressure Valve, 1 PSIG Vacuum Release, Up to 30 GPM The vent cap is equipped with valves that automatically compensate for changes of internal tank pressure due to temperature and fuel dispensing. Pressure cap valve opens at 3 PSIG to reduce tank pressure . Vacuum release opens at 1 PSIG as the tank cools . Lockable cap design provides added security and deters fuel theft (padlock not included) . Specially coated base to reduce rust . Allows fluid removal at up to 30 GPM. Compatible with diesel fuel (bio-diesel blends up to B20), gasoline (gasohol up to E15), kerosene and fuel oils. The vent cap is equipped with valves that automatically compensate for changes of internal tank pressure due to temperature and fuel dispensing.