This is the Poseidon Tech Counter Lung Pack for Rebreather Features:Capacity - The Technical Counter Lung capacity is 8.2 liters. The Tech Counter Lungs have the same features as the Recreational Counter Lungs, but with an increased lung volume to 8.2 liters and the possibility for the diver to manual inject oxygen and diluent gases into the loop. The Counter Lungs have two separate intakes for the two gases. On the exhalation lung are placed the injection for the oxygen and on the inhalation lung you will find the diluent air inflation. Both buttons are clearly marked so you don&';t fit the hoses in the wrong manner.