Apeks by Aqua Lung ATX40/DS4 Balanced Yoke Regulator The first stage is dry sealed keeping all internal components protected from the environment High performance regulator that boasts an over-balanced first stage with a pneumatically balanced second stage Four medium pressure ports and one high pressure port The 2nd stage uses a pneumatically balanced valve system for excellent breathing Due to the ATX 40s high efficiency heat exchanger system, it can cope with even the coldest conditions without freezing, making it the perfect all around regulator