Designed for Inert Gas Systems that produce only positive pressure on discharge, the Aerofoil balanced weighted blade system of the SHX model performs at a 100% efficiency at 95 Pascals. At 80 Pascals of enclosure pressure, the vent blades start to open, and at 95 Pascals, they open fully. The difference of 15 Pascals between partially open and 100% efficiency is a first in the world.