Enardo Dead Weight Thief Hatches are generally used on low-pressure, steel and fiberglass tanks.
When excessive pressure builds within the storage tank, the vent's hinged cover begins to open at the predetermined set pressure, relieving excess pressure. When the overpressure has dissipated, the cover reseats onto the base. When excessive vacuum builds within the storage tank, the spring-loaded pallet lifts, breaking the seal between the seat and pallet. The vacuum valve reseals upon relief.