The continuity equation in fluid flow states that the net rate of inflow into small volume must be zero. The principle of mass conservation for a steady, one-dimensional flow, with one inlet and one outlet. Q=A1V1=A2V2 This equation is called the continuity equation for steady one-dimensional flow. For a steady flow through a control volume with many inlets and outlets, the net mass flow must be zero, where inflows are negative and outflows are positive.