Apeks DS4DS4 First Stage As the diver descends the demand for air increases. To maintain the supply, the intermediate pressure increases relative to the water depth. In this dry sealed system hydrostatic pressure, acting on the outer sealing diaphragm, is transmitted to the primary diaphragm via the load transmitter. This first stage utilizes a unique over tracking (over balanced) diaphragm design, where the intermediate pressure supplied to the second stage