Venturi Control
The Apeks Integrated Venturi System (IVS) controls the air flow through the second stage, allowing air to flow directly through the mouthpiece to the diver or be re-directed against the diaphragm. The Venturi lever therefore acts as a pre-dive switch. Set in the minus position, the second stage cannot free-flow if accidently dropped in the water. When the diver begind to use the regulator, the lever can be switched to the plus position and the second stage then gives full Venturi assistance to the diver, reducing breathing effort.

Pneumatically Balanced System
Apeks second stages feature a Pneumatically Balanced Valve System. Air passes through the centre of the valve to a counter balance cylinder, which assists the spring in closing the valve. This eliminates the need for a heavier spring and thereby reduces the overall breathing effort.

Cracking Resistance Control
The ATX200, ATX100 and ATX50 second stages feature Cracking Resistance Control (CRC). This feature adjusts the spring load on the poppet valve assembly and so varies the cracking resistance, which can be adjusted during the dive to suit individual diver performance.

Balanced First Stage
The medium pressure output is constant, regardless of the cylinder pressure, and this is achieved by means of a counter balance chamber of similar area to the valve seat orifice. In addition, the demand for air increases as the diver descends. To help maintain the supply, the medium pressure is always 9.5 bar above ambient in the Apeks Dry Sealed System. This is achieved by transmitting hydrostatic pressure, acting on the outer diaphragm, to the primary diaghragm via the load transmitter. So, in short, due to the design of the first stages, the air supply should be constant regardless of the external dive conditions.