A flow controller is a differential pressure regulator designed to control minute gas flows with precision and keep a certain constant flow rate. Model 2203 Variable Secondary Pressure Flow Controller is a control valve that keeps mass flows at a constant rate under a given constant level of supply pressure even when the load pressure on the secondary side (outlet side) fluctuates, and its construction is designed so that the performance of its precision control over flows to the set flow rate is maintained by the incorporated precision needle valve without being affected by such fluctuations.