Rim vents are installed on floating roofs or cone roofs of
storage tanks with direct communication to the vapor
space. In floating roof tanks, rim vents provide pressure
relief to the roof and seals when a tank is empty, the roof
is landed, and the tank is being filled. In addition, pressure
relief to the seals can be achieved when the roof is floating
if product evaporation occurs. As the pressure in the vapor
space increases to the set point, the weight-loaded pallet
lifts vertically to allow the vapor space to relieve pressure.
As the pressure in the vapor space drops back below
the rim vent set point, the pallet lowers and closes. The
rim vent set point is adjustable by adding to or removing
weights from the pallet.